2816

Background: The human ortholog of Rabphillin-3A-Like gene (RPH3AL), located at 17p13.3 locus, has been first identified, cloned and sequenced in medulloblastoma. Recently, a study in colorectal cancer has reported missense point mutations in coding region of RPH3AL. In the present study, we assessed the mutational status of RPH3AL in colorectal adenocarcinomas (CRCs) and the mutations were correlated with clinicopathologic features. Methods: Fifty three randomly selected frozen tissues of invasive tumors as well as 53 matching normal (benign epithelium) samples were evaluated for the mutational status of the RPH3AL gene. These tissues were prospectively collected from patients who underwent surgery for CRC at University of Alabama at Birmingham from 1996 to 2004. The mutational status of this gene was assessed by direct sequencing of the cDNA covering all exons (1 through 9) including part of 5’ and 3’ untranslated regions (UTR). Results: In total, 40% (21 out of 53) of CRCs exhibited point mutations in RPH3AL, while 16 of these mutations were single nucleotide polymorphisms (SNPs). Two CRCs exhibited mutations at codon 67, and the remaining 3 at codons 98, 175, or 268. Mutations at codon 67, 175, or 268 were missense point mutations resulting in amino acid substitutions; whereas, alteration at codon 98 was a silent mutation (transition). All these four mutations are novel and were not reported earlier in any human malignancy including CRC. Seven of the 16 SNPs (or 7 of 53, 13%) were at -25 position in the 5’UTR of exon 2 of RPH3AL and designated as 5’UTR-25. The SNP at 5’UTR-25 was a change in the nucleotide from Cytosine to Adenine (transversion). The remaining 9 cases exhibited SNPs at codon 49 (3 cases), 62 (3 cases), or 303 (3 cases). Although mutation at 303 resulted in amino acid change (Alanine to Valine), it has been described as an allelic polymorphism in medulloblastoma, follicular thyroid carcinoma and ovarian carcinoma. Interestingly, all CRCs with SNPs at 5’UTR-25 were found to be lymph-node positive (pN1-3) cases. Furthermore, the incidence of SNPs at 5’UTR-25 was higher in Caucasian patients (6 of 31, 19%) compared to African-American patients (1 of 22, 5%). Conclusions: Our results suggest that the higher incidence of genetic alterations within the RAPH3AL gene might be involved in the pathogenesis of colorectal cancer. Also, these studies suggest that the 5’UTR-25 (C>A) variant of the RPH3AL gene may be involved in colorectal cancer invasion and metastasis. These studies are supported by a NCI/NIH grant RO1-CA98932-01.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]