Tissue-specific cancer-related serpin gene cluster at human chromosome band 3q26

Approximately one quarter of the identified human serpin genes are cancer-related and clustered mainly at two distinct loci: 6p25 and 18q21. We have studied a novel serpin gene cluster at 3q26 containing at least two recently identified members: the pancreas-specific protease inhibitor, pancpin (PI14), and the brain-associated protease inhibitor, neuroserpin (PI12). In this, unlike a previous study, both PI14 and PI12 at 3q26 were found to consist of 9 exons and 8 introns and to share a perfectly conserved gene organization whose pattern is very different from that of the ov-serpin family. This distinct pattern appears identical in the genomic structures of human plasminogen activator inhibitor-1 (PAI1) at 7q21 and protease nexin 1 (PI7) at 2q33-35, confirming that these four genes in three different chromosomes form a discrete subset within the serpin superfamily. As in the other three members whose gene expression is altered during tumorigenesis, PI12 expression was found to be down-regulated in tumor brain tissues and in two brain cancer cell lines: U-87 MG and H4. By screening genomic libraries, we isolated two overlapping clones showing that the marker SGC32223 (centromere) is located within intron F of PI12 and the marker WI-10077 (telomere) is located downstream of the 3'-flanking region of PI14. This finding indicates that the distance between human PI14 and PI12 is approximately 100 kb, and hence we speculate that other tissue-specific cancer-related serpin genes are likely to reside within this 3q26.1 cluster region.