Two type XVII collagen (BP180) mRNA transcripts in human keratinocytes: a long and a short form

We have analysed BP180 mRNA expression in normal human keratinocytes. Here we report the presence in normal keratinocytes of two COL17A1 transcripts w hich differ by 0.6 kb in length. Both mRNAs hybridized on Northern blot wit h probes directed to sequences encoding intracellular and extracellular fra gments of BP180. By blast homology search alignments we extended the 3' unt ranslated region (3'UTR) of the known BP180 mRNA sequence by 877 bases to c ompletion. Three of 20 cDNAs identified by blast searches contained a 610 b p deletion in this new 3'UTR sequence. Northern blot analysis with a probe complementary to this deleted sequence showed binding only to the larger mR NA. The deletion of 610 nucleotides in the smaller mRNA was verified by rev erse transcription-PCR and sequencing. Genomic PCR showed the new sequence to be an extension of exon 56 of the COL17A1 gene which suggests that the s econd mRNA is generated by differential splicing. In normal keratinocytes t he level of the smaller transcript was 5-15% of that of the larger transcri pt whereas in a squamous cell carcinoma cell line this ratio was reversed, the smaller mRNA being three times more abundant than the larger mRNA. The biological significance of this newly identified transcript in protein synt hesis and tissue expression or in cell differentiation, proliferation or ad hesion is as yet unknown.