Regulation of laminin beta2 chain gene expression in human cancer cell lines.

ABSTRACT

The laminin beta2 chain is a basement membrane component expressed in a tissue- and developmental stage-specific manner. In this report we have examined the transcriptional and post-transcriptional regulation of the human laminin 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 chain. Segments of the beta2 chain gene promoter region were cloned into luciferase reporter vectors, and their ability to stimulate transcription was tested by transient transfection. Sequences downstream of the transcription start site between nucleotides +91 and +120 were found to be essential for luciferase activity in the two cell lines. Additional positive regulatory regions were present further upstream, between nucleotides -164 to -667 and between nucleotides -667 to -1724. Genomic DNA at the 3' end of the gene also appeared to have enhancer activity, as a 1.1-kb fragment located downstream of the last exon stimulated the luciferase activity of the nucleotides -667/+297 promoter segment approximately threefold. Alternative splicing of the first intron of the human laminin beta2 chain gene generates two isoforms of the 5' untranslated region of the beta2 chain mRNA. The translational efficiencies of the two laminin beta2 chain leaders did not differ significantly, when assayed by polysome profile analysis of endogenous clone A cell beta2 chain mRNA, transient transfection of chimeric beta2 chain leader/luciferase expression plasmids in clone A cells, and translation of in vitro synthesized RNAs in rabbit reticulocyte lysates.