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The human ortholog of the Rabphillin-3A-Like gene (RPH3AL), located at the 17p13.3 locus, exhibited different variant forms and their varying prognostic values in colorectal adenocarcinoma (CRC). In this preliminary study, we assessed their molecular phenotypic features that are contributing to different clinical consequences.

Genotypic analysis of SNP at the -25 nucleotide site of the 5’untranslated region (5’UTR-25) of RPH3AL was performed on genomic DNA samples isolated from 37 CRCs and the matching control (benign) tissues. The archival tissue sections of all these cases were evaluated for immunohistochemical expression of different molecular markers of cell proliferation (Ki67), cell cycle (p53 & p27kip-1), apoptosis (Bax & Bcl-2) and cell adhesion (MUC1) using appropriate monoclonal antibodies. The cut-off values to categorize the tumors into positive or negative for the expression of these markers were determined based on their expression in the benign colonic epithelium. The cutoff values for nuclear staining of Ki67, p53, and p27kip-1, were ≥10%, ≥10%, and ≥50% positive malignant cells, respectively. The cytoplasmic staining for Bax, Bcl-2 and MUC1 were estimated using a semi-quantitative scoring on a scale of 0 to 4.0, and the cutoff values were ≥1.8, ≥0.5 and ≥0.5, respectively. The expression levels of these markers were correlated with the variant forms of the RPH3AL gene using the Chi-square test. Univariate Kaplan-Meier analysis was performed to assess the prognostic value of different variant forms of RPH3AL.

Out of 37 cases 12 were heterozygous (C/A allelic forms) and the remaining 25 were homozygous (23 were C/C and 2 were A/A) at 5’UTR-25 of RPH3AL. The A/A and C/C (17 of 25, 68%) variants of RPH3AL was more commonly observed in patients with advanced stage disease (Stage III & IV) than the patients with C/A variants (4 of 12, 33%) (χ2 P=0.04). Also, A/A and C/C variants of RPH3AL were associated with shorter patient survival than patients who exhibited C/A variants (logrank, P=0.028). CRCs with homozygous C/C or A/A variants have exhibited increased nuclear staining of Ki67 (18 of 25, 72%; χ2, P=0.01) and p27kip-1 (16 of 25, 64%; χ2 P=0.05) suggesting that these tumors are highly proliferative and aggressive in nature. However, nuclear accumulation of p53, expression of Bax, Bcl-2 or MUC1 was not correlated with the aggressive variant forms of RPH3AL.

The CRCs with genotypes C/C and A/A at 5’UTR-25 of the RPH3AL gene were associated with higher proliferation indicating that these tumors are more aggressive than those CRCs with the C/A genotype. This work is supported partially by funds from the Departmentof Pathology, University of Alabama at Birmingham and by a grantfrom the National Institute of Health/National Cancer Institute(RO1-CA98932-01).

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA