Cloning of cDNAs encoding human S‐100 α and β subunits and their differential expression in human tumor cell lines

Abstract

We isolated nearly full‐length clones of S‐100 α and β subunit cDNAs from a human brain cDNA library. The α subunit cDNA was 579 bp long and contained 99 bp of 5′‐noncoding region, 282 bp of coding region, and 198 bp of 3′‐noncoding region. The β subunit cDNA was 743 bp long and contained 57 bp of 5′‐noncoding region, 276 bp of coding region, and 410 bp of 3′‐noncoding region. An amino acid sequence comparison between human and bovine α subunits and between human and rat β subunits showed that both subunits were nearly entirely conserved. The amino acid sequences of human α and β subunits were conserved at both Ca²⁺‐binding domains. Northern blot analysis of brain RNA showed that human α and β subunit cDNA probes discriminated between α and β subunit mRNAs. By using these subunit‐specific cDNA probes, it was demonstrated that α and β subunit mRNAs were expressed in different manners among tumor cell lines: β was detected in melanoma and some glioma cell lines, while α was detected only in a melanoma cell line. Southern blot analysis showed that there were no major deletions and rearrangements of α and β subunit genes in these cell lines, regardless of the level of α and β subunit expression, suggesting that the expression of these subunits may be regulated at the transcriptional or RNA stability level.