Expression of the laminin-A chain is down-regulated by a non-canonical polyadenylation signal

Reduced expression of laminin alpha 3 and alpha 5 chains in non-small cell lung cancers

The basement membrane is considered to act as a barrier which hinders cancer cells from invading the surrounding stroma. In order to assess changes in essential components during neoplasia in the lung, we immunohistochemically studied distribution patterns of laminins alpha 3 and alpha 5 in 40 adenocarcinomas and 8 squamous cell carcinomas. The a 5 chain was generally preserved at the periphery, frequently disrupted in foci with alveolar collapse and absent in foci of fibroblastic proliferation within adenocarcinomas. Fragmentation and absence of laminin alpha 3 chain were more prominent than for alpha 5 chain. Laminin alpha 3 chain was partially fragmented or absent in peripheral areas of adenocarcinomas, being significantly different from alpha 5 chain. Non-small cell lung cancers with reduced alpha 5 chain showed a tendency for greater lymph node metastasis. In cultured normal air way epithelial cells, both laminin alpha 3 and alpha 5 chains were found to be expressed by northern analysis. Eleven of the twelve cultured lung cancer cell lines did not express alpha 3 chain and expression of alpha 5 chain was reduced in three. Quantitative RT-PCR analysis also demonstrated expression of laminin alpha 3 chain in adenocarcinoma tissues to be significantly lower than in normal lung tissues. These results suggest that expression of laminin alpha chains is often reduced in lung cancer cells and this might contribute to basement membrane fragmentation and subsequent proliferation of stromal elements, as well as play some role in the process of cancer cell invasion.

Expression of transmembrane serine protease TMPRSS2 in mouse and human tissues

The purpose of this study was to clarify the expression of TMPRSS2 in mice during development and to compare the tissue distribution of the transcripts in adult mouse and human tissues. Mouse TMPRSS2 cDNA was cloned; the predicted amino acid sequence contains 490 residues sharing 81.4% similarity with human TMPRSS2. According to northern blots, mouse TMPRSS2 is expressed mainly in the prostate and kidney, while human TMPRSS2 is expressed in the prostate, colon, stomach, and salivary gland. In situ hybridization analyses of mouse embryos and adult tissues revealed that TMPRSS2 was expressed in the epithelia of the gastrointestinal, urogenital, and respiratory tracts. Expression was very selective and constant after the gene was turned on during development. Expression of TMPRSS2 was localized in the luminal epithelial cells of the mouse and human prostate. The information presented here will be useful in further studies regarding the function and physiological significance of TMPRSS2.

Characterization of aflJ, a gene required for conversion of pathway intermediates to aflatoxin

The genes encoding the aflatoxin biosynthetic pathway enzymes have been localized as a cluster to a 75-kb DNA fragment. The enzymatic functions of the products of most of the genes in the cluster are known, but there are a few genes that have not yet been characterized. We report here the characterization of one of these genes, a gene designated aflJ. This gene resides in the cluster adjacent to the pathway regulatory gene, aflR, and the two genes are divergently transcribed. Disruption of aflJ in Aspergillus flavus results in a failure to produce aflatoxins and a failure to convert exogenously added pathway intermediates norsolorinic acid, sterigmatocystin, and O-methylsterigmatocystin to aflatoxin. The disrupted strain does, however, accumulate pksA, nor-1, ver-1, and omtA transcripts under conditions conducive to aflatoxin biosynthesis. Therefore, disruption of aflJ does not affect transcription of these genes, and aflJ does not appear to have a regulatory function similar to that of aflR. Sequence analysis of aflJ and its putative peptide, AflJ, did not reveal any enzymatic domains or significant similarities to proteins of known function. The putative peptide does contain three regions predicted to be membrane-spanning domains and a microbodies C-terminal targeting signal.

Molecular characterization of a serine/threonine kinase in the DiGeorge minimal critical region

The majority of patients with DiGeorge, velocardiofacial or conotruncal anomaly facial syndromes share a common genetic etiology, deletion of chromosomal region 22q11.2. This report describes a computational approach toward the identification and molecular characterization of a newly identified serine/threonine kinase from the minimal critical deleted region (MDGCR). A cosmid contig of the minimal critical region has been assembled and sequenced in its entirety. Database searches and computer analysis of one cosmid (111f11) for coding sequences identified two regions with high similarity to the mouse serine/threonine kinase, Tsk1. Our investigations demonstrate that one of these regions contains a testis-specific gene that undergoes differential splicing, while the other region is most likely a pseudogene. Northern blot analysis and cDNA cloning demonstrate that there is alternate processing of the 3'UTR without altering the conserved kinase domains within the open reading frame. Serine/threonine kinases can play a regulatory role and have been found to be expressed during early embryogenesis. Based on its position in the MDGCR and possible function, the gene reported here is a candidate for the features seen in the 22q11 deletion syndrome.

Expression of laminin and its possible role in adrenal cortex homeostasis

The adult mammalian adrenal cortex undergoes permanent regeneration. This process implies a cellular proliferation step restricted to the external zone of the tissue, and a subsequent centripetal cell migration during which phenotypic transition from glomerulosa into fasciculata and reticularis cells and elimination of senescent cells through apoptosis occur. As the molecular mechanisms implied in adrenocortical cell migration are still generally unknown, we addressed that question in the present study. Of several extracellular matrix proteins tested, laminin was the most potent chemotactic and haptotactic factor for bovine fasciculata adrenocortical cells. The maximal chemotactic effect (3-fold stimulation) was observed with 50-75 micrograms/ml laminin, whereas the haptotactic effect (3.5-fold stimulation) plateaued for laminin concentrations in the coating solution over 25 micrograms/ml. Using an anti-Engelbreth-Holm-Swarm laminin antibody, we could demonstrate that adrenocortical cells actively synthesize and secrete Engelbreth-Holm-Swarm-laminin, with the A chain produced in limiting quantities. ACTH treatment of adrenocortical cells specifically induced a 2.7- to 4.5-fold increase in A chain synthesis, resulting in a corresponding increase in the amount of secreted laminin. The distribution of laminin in the adrenal cortex tissue was then evaluated by standard immunohistochemistry. The protein appeared to be uniformly expressed in the three zones of the cortex. This observation does not favor the hypothesis that laminin acts as an attractant driving centripetal cell migration. Laminin, which is synthesized under the control of the systemic hormone ACTH, appears as a permissive factor that facilitates proper homeostasis of the adrenocortical tissue.

The assembly of laminin-5 subunits

Laminin-5 is a heterotrimer composed of alpha 3, beta 3, and gamma 2 chains, produced by keratinocytes and the human squamous cell carcinoma line (SCC-25), and is one of the candidate proteins for the genetic lesion in junctional epidermolysis bullosa. Two-dimensional SDS-polyacrylamide gel electrophoresis (first dimension, nonreducing conditions; second dimension, reducing conditions) revealed that the immunoprecipitated laminin-5 from a SCC-25 cell fraction consisted of alpha 3, beta 3, and gamma 2 monomers, a beta 3 gamma 2 heterodimer, and an alpha 3 beta 3 gamma 2 heterotrimer. The presence of the beta 3 gamma 2 heterodimer, but not heterodimers containing an alpha 3 chain and any of the other chains, was suggestive of assembly of laminin-5 proceeding from a beta 3 gamma 2 heterodimer to an alpha 3 beta 3 gamma 2 heterotrimer. We showed, by cotransfection experiments using full-length recombinant beta 3 and gamma 2 chains in a human cell line devoid of endogenous laminin-5, that stable heterodimers can be formed in the absence of alpha 3 chain expression. In the SCC-25 cell fraction, the alpha 3 monomer pool was the smallest of the monomers. Pulse-chase experiments using the cell fraction also indicated that the heterotrimer was assembled after a 10-min pulse and was nearly absent after a 24-h chase. These results are consistent with the synthesis of alpha 3 being limiting for heterotrimer assembly, with rapid association of the alpha 3 chain with beta 3 gamma 2 heterodimers to form complete heterotrimers. Treatment with tunicamycin reduced the size of each of the laminin-5 subunits, indicating that all chains are glycosylated, but that N-linked glycosylation is not necessary for chain assembly and secretion.