CHC1-L, a candidate gene for prostate carcinogenesis at 13q14.2, is frequently affected by loss of heterozygosity and underexpressed in human prostate cancer

Loss of heterozygosity (LOH) at chromosome 13q14 is one of the most recurrent anomalies observed in sporadic prostate tumors. This LOH is believed to unmask recessive mutations that inactivate a tumor-suppressor gene(s) which otherwise regulates normal cell growth and suppresses abnormal cell proliferation. Identification of potential tumor-suppressor genes within the deleted region is a way of indicating putative pathways of prostate cancer development and progression. The main target that disappears or is down-regulated as a result of 13q14 loss remains to be identified. Therefore, our first concern was to find a gene located in the 13q14 region whose transcription is reduced. CHCI-L, for chromosome condensation I-like, is mapped to the smallest common deleted region. CHCI-L expression is significantly reduced in prostate tumors compared to normal prostate tissues (p = 0.0002). In 21 of 36 (58%) primary prostate tumors studied, CHCI-L expression was reduced at least 2-fold, as measured by real-time quantitative RT-PCR; 18 of the tumors (50%) showed 13q14 LOH for at least I of the 5 polymorphic markers that we studied in the region, and 14 (78%) of these were among the tumors underexpressing CHCI-L. CHCI-L is alternatively spliced at its 5' end to produce 2 isoforms, of 551 and 526 aa. Analyses of CHCI-L integrity and of the quantitative expression of its variants indicate that the observed underexpression in prostate tumors is related to reduced expression of the 55 1 aa isoform. Although CHCI-L is not the obvious candidate given its only known homology, to RCCI, a guanine nucleotide exchange factor for the Ras-related GTPase Ran, the frequent significant decrease observed in its expression in prostate cancer associated with the difference in frequency of CHCI-L variant isoforms between normal and neoplastic prostate tissues places it in a pivotal role or possibly adjacent to a gene tat has that role in prostate cancer evolution. (C) 2002 Wiley-Liss, Inc.