Laminins are heterotrimeric molecules found in all basement membranes. In mammals, they have been involved in diverse developmental processes, from gastrulation to tissue maintenance. The Drosophila genome encodes two laminin alpha chains, one beta and one gamma, which form two distinct laminin trimers. So far, only mutations affecting one or other trimer have been analysed. In order to study embryonic development in the complete absence of laminins, we mutated the gene encoding the sole laminin beta chain in Drosophila, LanB1, so that no trimers can be made. We show that LanB1 mutant embryos develop until the end of embryogenesis. Electron microscopy analysis of mutant embryos reveals that the basement membranes are absent and the remaining extracellular material appears disorganised and diffuse. Accordingly, abnormal accumulation of major basement membrane components, such as Collagen IV and Perlecan, is observed in mutant tissues. In addition, we show that elimination of LanB1 prevents the normal morphogenesis of most organs and tissues, including the gut, trachea, muscles and nervous system. In spite of the above structural roles for laminins, our results unravel novel functions in cell adhesion, migration and rearrangement. We propose that while an early function of laminins in gastrulation is not conserved in Drosophila and mammals, their function in basement membrane assembly and organogenesis seems to be maintained throughout evolution.

Laminin-332 (LN-332) is a basement membrane component known to exert a beneficial effect on rat pancreatic beta cells in vitro. In this work, we analyzed the expression of LN-332 in human islets, its expression after inflammatory insults by cytokines, and the molecular mechanisms responsible for this effect. By Western blotting and RT-PCR, we showed that LN-332 was expressed in isolated human islets. By immunofluorescence on pancreas sections, we observed that labeling was confined to endocrine cells in islets. Confocal microscopy analysis on isolated islet cells revealed that labeling was granular but did not colocalize with hormone secretory granules. LN-332 was most abundant in cultured islets compared to freshly isolated islets and was found in culture medium, which suggests that it was secreted by islets. When islets were exposed to interleukin (IL)-1beta, expression and secretion of LN-332 increased as compared to control. No effect was observed with tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K) activity, inhibited culture- and IL-1beta-induced LN-332 expression in islets. These results show that LN-332, known to have some beneficial effect on beta cells in vitro, is produced and secreted by endocrine islet cells and is up-regulated by stressing conditions such as culture and IL-1beta-exposure.-Armanet, M., Wojtusciszyn, A., Morel, P., Parnaud, G., Rousselle, P., Sinigaglia, C., Berney, T., Bosco, D. Regulated laminin-332 expression in human islets of Langerhans.

A three compartment model (ER --> Golgi --> extracellular medium) is used here to describe the interorganelle transport and final secretion of an IgG(2a) monoclonal antibody (MAb) in 9.2.27 murine hybridoma cells. Model simulations of pulse-chase and continuous labeling experiments are used to gain a better understanding of the kinetics of MAb interorganelle traffic. Simulation results for the continuous labeling case compare well with experimental data obtained during continuous labeling of 9.2.27 hybridoma cells. Incorporation of this compartmental transport model into our previously developed model of MAb synthesis and assembly can provide a useful tool for analyzing the dynamics and regulation of the complete antibody secretory pathway under different growth and/or nutritional conditions.

Two human squamous carcinoma cell lines and human diploid fibroblasts were examined for the production of extracellular matrix (ECM) molecules including fibronectin (FN), laminin (LN), and thrombospondin (TSP) when grown on a number of different substrates. The substrates used included glass, plastic, collagen (gelatin), and DEAE-dextran. Levels of TSP as indicated by enzyme-linked immunosorbent assay did not vary significantly as a function of substrate. In contrast, LN levels in the culture medium were significantly decreased when the cells were grown on DEAE-dextran or collagen-linked dextran as compared to the other substrates. FN levels were slightly lower in the culture medium of the cells grown on DEAE-dextran. Biosynthetic labeling followed by immunoprecipitation indicated that the reduction in LN was due, in part, to decreased biosynthesis. Previous studies have indicated that LN influences the behavior of epithelial cells in culture and that the cells, themselves, are a major source of the LN. The differences in LN production noted here indicate that the production of this ECM component is influenced by the substratum on which the cells are grown. These differences could contribute to alterations in biological properties that are known to be influenced by the substratum.

The 67LR (67 kDa laminin receptor) is a cell-surface receptor with high affinity for its primary ligand. Its role as a laminin receptor makes it an important molecule both in cell adhesion to the basement membrane and in signalling transduction following this binding event. The protein also plays critical roles in the metastasis of tumour cells. Isolation of the protein from either normal or cancerous cells results in a product with an approx. molecular mass of 67 kDa. This protein is believed to be derived from a smaller precursor, the 37LRP (37 kDa laminin receptor precursor). However, the precise mechanism by which cytoplasmic 37LRP becomes cell-membrane-embedded 67LR is unclear. The process may involve post-translational fatty acylation of the protein combined with either homo- or hetero-dimerization, possibly with a galectin-3-epitope-containing partner. Furthermore, it has become clear that acting as a receptor for laminin is not the only function of this protein. 67LR also acts as a receptor for viruses, such as Sindbis virus and dengue virus, and is involved with internalization of the prion protein. Interestingly, unmodified 37LRP is a ribosomal component and homologues of this protein are found in all five kingdoms. In addition, it appears to be strongly associated with histones in the eukaryotic cell nucleus, although the precise role of these interactions is not clear. Here we review the current understanding of the structure and function of this molecule, as well as highlighting areas requiring further research.

OBJECTIVES: To develop a new toxic gene therapy using the tissue-specific human chorionic gonadotropin-beta (hCG-beta) promoter for testicular cancer. Although most patients presenting with disseminated testicular tumor are cured through the use of chemotherapy with or without surgery, those patients with relapse after initial therapy present a difficult clinical problem. The serum tumor marker hCG-beta is frequently elevated in patients with testicular cancer, and the pretreatment and post-treatment levels of serum hCG-beta are highly predictive of treatment outcome. METHODS: Human testicular embryonal carcinoma cell line, NEC 8, a human prostate cancer cell line, PC-3, and a human bladder cancer cell line, WH, were used in this study. A transient expression experiment was used to analyze the activity of a 729-bp hCG-beta promoter in all three cell lines. A recombinant adenovirus carrying thymidine kinase (Ad-hCG-beta-TK) under control of the hCG-beta promoter was generated. The tissue-specific activity of Ad-hCG-beta-TK was tested in vitro and in vivo. RESULTS: The hCG-beta promoter had significantly greater activity in the hCG-beta-producing cell line (NEC 8) than in the non-hCG-beta-producing cell lines (PC-3 and WH). In vitro, Ad-hCG-beta-TK with acyclovir significantly inhibited NEC 8 growth but not PC-3 or WH cell growth. In vivo, Ad-hCG-beta-TK with acyclovir significantly inhibited NEC 8 subcutaneous tumor growth in nude mice. CONCLUSIONS: In this study, we explored the possibility of developing a new therapeutic agent to target and induce the killing of testicular germ cell tumor selectively by using tissue-specific hCG-beta promoters.

Increased expression of laminin and various cytokines, including interferon-y (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) has been demonstrated in minor salivary glands from patients with Sjögren's syndrome. Previous reports state that exposure of a human salivary-gland cell line (HSG) to IFN-gamma results in cellular changes similar to those in vivo Sjögren's syndrome. To begin studies of the cause of increased laminin expression in salivary glands in Sjögren's syndrome and laminin's role in the pathological process, the effects of IFN-gamma on laminin expression and growth of HSG cells were examined here. Subconfluent cultures of HSG cells were treated or not with IFN-gamma (1000 units/ml) for 1, 3 or 6 days. Immunoprecipitation showed that the expression of cell-associated laminin was significantly greater in IFN-gamma-treated cells at 3 or 6 days than in untreated cells, while no significant differences in laminin counts precipitated from the media were evident among any of the IFN-gamma-treated or untreated samples. Western blot analysis strongly suggested that this immunoprecipitated product is a dimer of the beta- and gamma-chains of laminin. Intracellular laminin was demonstrated immunocytochemically in a distinct, perinuclear pattern in both cytokine-treated and untreated cells. However, only faint staining for type IV collagen, and no staining for fibronectin were evident in untreated and cytokine-treated cells. An RNase protection assay showed only slight upregulation of the laminin beta-chain mRNA at 3 days, but no significant difference at 6 days of treatment. Taken together, these data suggest enhanced accumulation of a dimer of laminin beta- and gamma-chains in the cytoplasm of cytokine-treated HSG cells. However, mRNA for glyceraldehyde 3-phosphate dehydrogenase was significantly reduced at 6 days of treatment, suggestive of cytokine-mediated metabolic abnormalities. IFN-gamma treatment also resulted in significant reductions in cell numbers over time, in agreement with previous reports. Treatment of HSG cells for 3 days with IFN-gamma (1000 U/ml) and TNF-alpha (20 U/ml) resulted in no significant changes in cell proliferation or laminin protein and/or mRNA species compared to cells treated with IFN-gamma alone. Karyotype analysis of HSG cells revealed human chromosomes with triploid chromosome numbers and rearrangements, characteristic of transformed cells. These data demonstrate that IFN-gamma increases the amount of intracellular laminin beta-gamma dimers while decreasing cell growth. Further studies are required to define an interaction between laminin expression and the growth and viability of HSG cells.

The expression pattern of laminin (Ln) alpha1 chain has been a controversial topic due to discrepancies between mRNA and protein studies. Recently it was reported that the monoclonal antibody 4C7, previously thought to recognize Ln alpha1 chain, actually detects Ln alpha5 chain. This finding makes it necessary to reestimate the role of Ln alpha1 chain and to compare the expression and functions of Ln alpha1 and alpha5 chains. We studied the expression of Ln alpha1 and alpha5 chains and production of Ln-1 and Ln-10 in cultured human carcinoma cells. Ln alpha1 chain mRNA was detected in JAR choriocarcinoma cells and in all four renal cell carcinoma cell lines studied. In contrast, pancreatic, colon, and lung alveolar carcinoma cell lines did not express or produce Ln alpha1 chain, suggesting that Ln-1 (alpha1 beta1 gamma1) is produced only by certain carcinoma cells. Ln alpha5 chain mRNA was expressed in all carcinoma cells, but was not incorporated into extracellular matrix in vitro, as shown with JAR cells. Immunoprecipitation of metabolically labeled cells showed that cells expressing Ln alpha1 mRNA also produced 400-kDa Ln alpha1 chain, whereas all cells produced 380-kDa Ln alpha5 chain. Adhesion to Ln-1 was inhibited by a functionally blocking antibody against alpha6-integrin subunit, whereas adhesion to Ln-10 was inhibited by an antibody against alpha6-integrin in JAR cells and by an antibody against alpha3-integrin in PANC-1 cells. The results suggest that Ln-10 is a ubiquitously expressed Ln isoform in carcinoma cells, and the mechanism of adhesion to Ln-10 is cell-type specific.

The LAMC1 gene coding for the laminin gamma1 subunit was targeted by homologous recombination in mouse embryonic stem cells. Mice heterozygous for the mutation had a normal phenotype and were fertile, whereas homozygous mutant embryos did not survive beyond day 5.5 post coitum. These embryos lacked basement membranes and although the blastocysts had expanded, primitive endoderm cells remained in the inner cell mass, and the parietal yolk sac did not develop. Cultured embryonic stem cells appeared normal after targeting both LAMC1 genes, but the embryoid bodies derived from them also lacked basement membranes, having disorganized extracellular deposits of the basement membrane proteins collagen IV and perlecan, and the cells failed to differentiate into stable myotubes. Secretion of the linking protein nidogen and a truncated laminin alpha1 subunit did occur, but these were not deposited in the extracellular matrix. These results show that the laminin gamma1 subunit is necessary for laminin assembly and that laminin is in turn essential for the organization of other basement membrane components in vivo and in vitro. Surprisingly, basement membranes are not necessary for the formation of the first epithelium to develop during embryogenesis, but first become required for extra embryonic endoderm differentiation.

BeWo is a choriocarcinoma cell line that generates an extracellular matrix (ECM) rich in laminin and is a useful model for human trophoblast. Immunofluorescence with monoclonal antibodies demonstrates that BeWo ECM contains laminin subunits beta1 and gamma1. Immunoprecipitation from conditioned medium shows that the cells secrete two distinct laminin trimers both containing beta1 and gamma1 but with alpha subunits of approx. 400 and 450 kDa. The culture medium also contains a species thought to be beta1 gamma1 dimer. Immunoprecipitation with monoclonal antibody 4C7, previously thought to recognize the alpha1 subunit, isolates complexes containing only the smaller alpha subunit. A second complex containing the larger alpha subunit along with beta1, gamma1 and a 150 kDa polypeptide is precipitated from 4C7-depleted medium with an anti-(laminin 1) polyclonal antibody. Peptide sequencing demonstrates that the 4C7-reactive species is alpha5, which is present as two similarly sized polypeptides. mRNA species encoding laminin subunits alpha1, alpha5, beta1, beta2 and gamma1 are all present in the cells. These results demonstrate the secretion of a novel laminin isoform, laminin 10, the subunit composition of which is alpha5 beta1 gamma1. Laminin 1 is also produced. No evidence for the secretion of beta2-containing laminin isoforms could be derived despite the presence of beta2 mRNA. Analysis with reverse transcriptase-mediated PCR also showed the presence of laminin alpha5 in first-trimester placenta and decidua.

Junctional epidermolysis bullosa (JEB) is an autosomal recessive skin blistering disease with both lethal and nonlethal forms, with most patients shown to have defects in laminin-5. We analyzed the location of mutations, gene expression levels, and protein chain assembly of the laminin-5 heterotrimer in six JEB patients to determine how the type of genetic lesion influences the pathophysiology of JEB. Mutations within laminin-5 genes were diversely located, with the most severe forms of JEB correlating best with premature termination codons, rather than mapping to any particular protein domain. In all six JEB patients, the laminin-5 assembly intermediates we observed were as predicted by our previous work indicating that the alpha3beta3gamma2 heterotrimer assembles intracellularly via a beta3gamma2 heterodimer intermediate. Since assembly precedes secretion, mutations that disrupt protein-protein interactions needed for assembly are predicted to limit the secretion of laminin-5, and likely to interfere with function. However, our data indicate that typically the most severe mutations diminish mRNA stability, and serve as functional null alleles that block chain assembly by resulting in either a deficiency (in the nonlethal mitis variety) or a complete absence (in lethal Herlitz-JEB) of one of the chains needed for laminin-5 heterotrimer assembly.

Tooth morphogenesis is regulated by epithelial-mesenchymal interactions mediated by the basement membrane (BM). Laminins are major glycoprotein components of the BMs, which are involved in several cellular activities. The expression and localization of the alpha3, beta3, and gamma2 laminin-5 subunits have been analyzed by in situ hybridization and immunohistochemistry during mouse molar development. Initially (E12), mRNAs of all subunits were detected in the entire dental epithelium and the corresponding proteins were located in the BM. During cap formation (E13-14), transcripts for the alpha3 and gamma2 subunits were localized in the outer dental epithelium (ODE), whereas the beta3 subunit mRNA was present in the inner dental epithelium (IDE). During the early bell stage (E16), immunoreactivity for all subunits disappeared from the BM along the IDE, although intense signals for beta3 mRNA were detectable in cells of the IDE. Subsequently, when the dentinal matrix was secreted by odontoblasts (E18-19.5), mRNAs of all three subunits were re-expressed by ameloblasts, and the corresponding proteins were detected in ameloblasts and in the enamel matrix. Tissue recombination experiments demonstrated that when E16 IDE or ODE was associated with E18 dental papilla mesenchyme, immunostaining for all laminin-5 subunits disappeared from the BM, whereas when cultured with non-dental limb bud mesenchyme, they remained positive after 48 hr of culture. These results suggest that the temporospatial expression of laminin-5 subunits in tooth development, which appears to be differentially controlled by the dental mesenchyme, might be related to the enamel organ histo-morphogenesis and the ameloblast differentiation.

The aim of this study was to determine the extent to which sulfate incorporated into biosynthesized basement membrane (BM) components increased as isolated type II cells progress toward a more type I cell-like phenotype from 7 to 21 days in culture. Specific sulfate cytochemistry, using high iron diamine, showed that type I-like cells in 21-day cultures deposited a more highly sulfated extracellular matrix. Biosynthetic labeling experiments using [35S]cysteine or [35S]sulfate as precursors confirmed the increased capacity of 21-day type I-like cells to biosynthesize sulfated BM components compared with type II-like cells in 7-day cultures, including a novel sulfated laminin. These biochemical changes in sulfation of BM components coincide with the established phenotypic transition from type II to type I cells during prolonged culture. More importantly, the data suggest that regulation of sulfation constitutes a potential mechanism by which type I and type II cells alter their environment in such a manner as to stabilize phenotype and modulate responses to growth factors.

We studied the distribution of laminin (Ln) chains and their integrin (Int) receptors in normal developing and adult and in atrophied human testes by using immunohistochemistry. Immunostaining for EHS Ln and type IV collagen was used to identify basement membranes (BMs). In the BM of seminiferous epithelium of fetal testis, a panel of monoclonal antibodies showed immunoreactivity for Ln alpha 1-, alpha 2-, beta 1-, beta 2- and gamma 1-chains, suggestive of the presence of Lns 1 to 3. In BM of adult seminiferous epithelium with active spermatogenesis, immunoreactivity for Ln beta 2- and gamma 1-chains was found but not for Ln alpha-chains, suggesting a complex of Ln chains not compatible with any known trimers. Instead, with polyclonal Ln antiserum and monoclonal antibody to type IV collagen, a distinct BM-like reactivity was seen. In atrophied testes, prominent immunoreactivities for Ln chains, compatible with Lns 1 to 3, were seen in the thickened BM of seminiferous tubules, hence suggestive of reappearance of fetal Lns. Among the subunits of Ln-binding Int receptors in fetal seminiferous tubules, a strong immunoreactivity for Int beta 1- and Int alpha 6-subunits was seen throughout the seminiferous epithelium, other Int subunits being found in interstitial cells. In the adult and atrophied testes, immunoreactivities for Int beta 1- and Int alpha 6-subunits were seen to be confined to the basal aspect of the seminiferous epithelium whereas immunoreactivities for Int alpha 1-, alpha 2-, alpha 3- and beta 4-subunits were seen in the myoid cells. The results show that both maturation and degenerative changes of human testes are accompanied by distinct changes in the Ln expression of BM of seminiferous epithelium, which appears to accompany epithelial differentiation of the Sertoli cells. Furthermore, they suggest the presence of a novel Ln trimer in BM of adult human seminiferous tubules.

The laminins are a family of structural basement membrane components with major influences on cells. They are high molecular weight glycoproteins composed of three different but homologous chains, alpha, beta and gamma. At present 10 different chains have been identified. Each chain has a distinct structural organization of domains, some of which have been assigned biological activities, including self-assembly and interactions with other proteins. The particular importance of laminins for the formation and stability of cell adhesion complexes is highlighted in severe inherited diseases of muscle and skin. Merosin is the collective name for laminins that share a common subunit, the laminin alpha 2 chain. Merosin-deficient congenital muscular dystrophy (CMD) is caused by mutations in the laminin alpha 2 chain gene. The skin disease Herlitz junctional epidermolysis bullosa is caused by mutations in any of the laminin alpha 3, beta 3 or gamma 2 chain genes. The medical importance of laminins provides a further impetus to study the basic structure-function relationships in laminins in order to understand genotype-phenotype relationships and to design prenatal diagnostic tests and therapies aimed at compensating for specific defects.

Extracellular matrix molecules are often very large and made up of several independent domains, frequently with autonomous activities. Laminin is no exception. A number of globular and rod-like domains can be identified in laminin and its isoforms by sequence analysis as well as by electron microscopy. Here we present the structure-function relations in laminins by examination of their individual domains. This approach to viewing laminin is based on recent results from several laboratories. First, some mutations in laminin genes that cause disease have affected single laminin domains, and some laminin isoforms lack particular domains. These mutants and isoforms are informative with regard to the activities of the mutated and missing domains. These mutants and isoforms are informative with regard to the activities of the mutated and missing domains. Second, laminin-like domains have now been found in a number of other proteins, and data on these proteins may be informative in terms of structure-function relationships in laminin. Finally, a large body of data has accumulated on the structure and activities of proteolytic fragments, recombinant fragments, and synthetic peptides from laminin. The proposed activities of these domains can now be confirmed and extended by in vivo experiments.

The expression of the constituent alpha 1 chain of laminin-1, a major component of basement membranes, is markedly regulated during development and differentiation. We have designed an antisense RNA strategy to analyze the direct involvement of the alpha 1 chain in laminin assembly, basement membrane formation, and cell differentiation. We report that the absence of alpha 1-chain expression, resulting from the stable transfection of the human colonic cancer Caco2 cells with an eukaryotic expression vector comprising a cDNA fragment of the alpha 1 chain inserted in an antisense orientation, led to (a) an incorrect secretion of the two other constituent chains of laminin-1, the beta 1/gamma 1 chains,(b) the lack of basement membrane assembly when Caco2-deficient cells were cultured on top of fibroblasts, assessed by the absence of collagen IV and nidogen deposition, and (c) changes in the structural polarity of cells accompanied by the inhibition of an apical digestive enzyme, sucrase-isomaltase. The results demonstrate that the alpha 1 chain is required for secretion of laminin-1 and for the assembly of basement membrane network. Furthermore, expression of the laminin alpha 1-chain gene may be a regulatory element in determining cell differentiation.

Laminin, a basement membrane glycoprotein, is a heterotrimer with alpha, beta, and gamma chains held together by a triple-stranded alpha-helical coiled-coil structure. Recently, a short peptide sequence at the C-terminus of the alpha-helical domain of each chain was identified as a critical site for the initiation of laminin chain assembly. Synthetic peptides, B1 and B2 (51-mers from the mouse laminin beta 1 and gamma 1 chains respectively) and M (55-mer from the laminin alpha 2 chain), containing these sites were able to assemble into a triple-stranded coiled-coil structure with chain-specific interactions [Nomizu, M., Otaka, A., Utani, A., Roller, P. P.,& Yamada, Y.(1994) J. Biol. Chem. 269, 30386-30392]. Here we focus on the mechanism of laminin assembly and examine the conformation and stability of the peptides under various conditions using circular dichroism (CD) spectroscopy. Dependence on chain length for the conformation and stability of trimers suggests that 51-mers for laminin beta 1 and gamma 1 chains and a 55-mer for the laminin alpha 2 chain are critical to attain high thermal stability (T m = 62 degrees C), similar to the larger fragments (approximately 200-mers) and to intact laminins. Since the conformation and stability are dependent on pH and the B1 and B2 monomers and the B1-B2 dimer conformations are partially destroyed at neutral pH, it is likely that they contain intra- and/or interchain repulsions by acidic residues. Moreover, the B1-B2 dimer was significantly more stable under acidic conditions, while the B1-B2/M trimer appears to dissociate into separate B1-B2 and M peptides at pH 2. Urea-induced denaturation showed that the B1-B2/M was more stable than the B1-B2, while both complexes showed virtually identical guanidine hydrochloride denaturation curves. Our data indicate that ionic interactions between B1-B2 and M are critical for the specific trimer formation. We propose a mechanism for laminin assembly:(1) A heterodimer B1-B2 is preferentially formed and creates an acidic pocket which provides a less stable structure due to intra- and intermolecular repulsions between acidic amino acids.(2) A basic site in the M peptide interacts specifically with the acidic pocket of the B1-B2 dimer and results in assembly into a more stable triple-stranded coiled-coil structure.

Laminin is a heterotrimeric glycoprotein found in the perisinusoidal space of adult rat liver. The principal cellular source of laminin in liver is the lipocyte, with its three subunits measuring 324, 200 and 200 kD. The large subunit of lipocyte-derived laminin is distinct from the A subunit of murine laminin (440 kD); its size suggests that it represents a peptide, called M, recently cloned from human placenta. Using oligonucleotide primers derived from the human M-subunit cDNA, we amplified a 445-bp sequence encoding a fragment of M-laminin from adult rat lipocytes. The rat cDNA is 90% homologous to the human M-subunit cDNA and recognizes an mRNA in lipocytes measuring about 10 kb. M-subunit transcripts were identified only in lipocytes from normal adult liver; they could not be identified in hepatocytes, endothelial cells or Kupffer cells. Lipocytes were screened for M-subunit protein with a polyclonal M antiserum. Cells stained specifically for the M-subunit after 36 hr in primary culture; the protein was also identified in freshly isolated cells by means of immunoblotting. To determine whether lipocytes alter their expression of the laminin M subunit during liver injury, we monitored M-subunit mRNA in these cells at various intervals after carbon tetrachloride administration. M-subunit transcripts increased twofold within 12 hr of toxin exposure, returning to below baseline by 48 hr. The results indicate that lipocytes produce the M subunit of laminin in place of A. Production of this subunit by lipocytes may facilitate cell growth and reorganization during liver regeneration.

Laminin has been previously shown to participate in tumor invasion and metastasis. Tumorigenesis by human prostate cell lines can be influenced by exogenous laminin. We have found that the human prostate tumor cell lines DU145, LNCaP, and PC-3 produce a variant form of the B1 chain of laminin, known as S-laminin. DU145 cells produce laminin containing a ratio of A:B1:B2:S of 1.8:1.0:2.5:1.0, respectively, compared to LNCaP cells, which have a ratio of A:B1:B2:S of 1.0:0:10.0:2.5. Kinetic analysis of laminin production showed that LNCaP cells retained most of their laminin production and secreted laminin forms characterized by decreased levels of n-acetyl glucosamine and sialic acid. In contrast, DU145 cells secreted most of their laminin in mature forms. LNCaP cells bound very little laminin to their surface. These features of LNCaP cells could contribute to their documented low adhesivity in vitro and its nontumorigenic phenotype.