An integrated physical and gene map of the 3.5-Mb chromosome 3p21.3 (AP20) region implicated in major human epithelial malignancies.

To facilitate the identification of tumor suppressor genes in the chromosome 3p21.3-p22 AP20 subregion, we constructed a 3.5-Mb physical and gene map of this segment (between markers D3S4285 and D3S3873) that spans the distance from 124.4cR3000 to 133.5 cR3000 of the GB4 genetic map. We used NotI-linking and -jumping clones, sequence-tagged site PCR marker analysis, and multicolor and fiber fluorescence in situ hybridization to confirm the sequence order and map orientation. An integrated clone contig composed of 5 yeast artificial chromosome, 15 bacterial artificial chromosome, 5 P1 artificial chromosome, and 8 NotI-linking clones provided the physical base of the map. We unequivocally established the order of 28 sequence-tagged sites and 35 genes in the region. Gaps between published bacterial artificial chromosome contigs were determined and covered by our own sequence data. Furthermore, three new genes were isolated, namely the human homologue to the rat Golgi peripheral membrane protein p65, GOLPH5 (GORASP1), the gene for stress-inducible protein, STI2, and the AP20-region gene 1, APRG1. The tumor suppressor gene candidate APRG1 was positioned close to the border of the homozygous deletion in a small cell lung cancer cell line ACC-LC5. Expression analysis with a tissue-specific panel of cDNA revealed seven distinct tissue-specific splice variants (A-G) of the message (size range, 1.0-1.8 kb). Although the gene was expressed at a low level in all tested tissues, comparatively higher expression was detected in pancreas (splice forms B and D), kidney (A) and placenta (B and C). The APRG1 gene encoded a predicted protein of 170 amino acids (isoform B), which had an NH2-terminal part conserved among members of the eukaryotic translation factor 6 gene family. A Prosite pattern corresponding to the cell attachment sequence Arg-Gly-Asp was also found. The presence of this domain raised the intriguing possibility that APRG1B may be directly involved in membrane interactions and cell adhesion. We showed that the AP20 region was duplicated during mammalian evolution and homologous gene clusters were present in human chromosome 2 and syntenic mouse regions on chromosomes 1, 2, and 9. Interestingly, the HYA22 gene (human ortholog of the yeast YA22 gene) was located at the borders of both breakpoints, evolutionarily conserved gene cluster and homozygous deletions detected in lung, kidney and other cancers. NotI digestion revealed that the AP20 region was frequently and extensively methylated in renal carcinoma cell lines and tumor biopsies.