Regulation of laminin beta 2 chain gene expression in human cancer cell lines

The laminin beta2 chain is a basement membrane component expressed in a tis sue- and developmental stage-specific manner. In this report we have examin ed the transcriptional and post-transcriptional regulation of the human lam inin beta2 chain in human tumor cell lines. Both the A204 rhabdomyosarcoma and clone A colon carcinoma cells express the laminin beta2 chain mRNA, but only the A204 cells secrete laminin heterotrimers containing the beta2 cha in. Segments of the beta2 chain gene promoter region were cloned into lucif erase reporter vectors, and their ability to stimulate transcription was te sted by transient transfection. Sequences downstream of the transcription s tart site between nucleotides +91 and +120 were found to be essential for l uciferase activity in the two cell lines. Additional positive regulatory re gions were present further upstream, between nucleotides - 164 to -667 and between nucleotides -667 to -1724. Genomic DNA at the 3' end of the gene al so appeared to have enhancer activity, as a 1.1-kb fragment located downstr eam of the last exon stimulated the luciferase activity of the nucleotides -667/+297 promoter segment approximate to threefold. Alternative splicing o f the first intron of the human laminin beta2 chain gene generates two isof orms of the 5' untranslated region of the beta2 chain mRNA. The translation al efficiencies of the two laminin beta2 chain leaders did not differ signi ficantly, when assayed by polysome profile analysis of endogenous clone A c ell beta2 chain mRNA, transient transfection of chimeric beta2 chain leader /luciferase expression plasmids in clone A cells, and translation of in vit ro synthesized RNAs in rabbit reticulocyte lysates.