Expression and therapeutic potential of the ubiquitin-conjugating enzyme E2C in esophageal adenocarcinoma Free

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Ubiquitin-dependent proteolysis of cyclins plays a critical role in cell-cycle progression and tumorigenesis. We investigated expression of the ubiquitin-conjugating enzyme E2C (UBE2C) during progression from Barrett’s metaplasia to adenocarcinoma, as well as the therapeutic potential of targeting this enzyme in esophageal adenocarcinoma cell lines. Using oligonucleotide microarrays to evaluate 46 esophageal samples, we found that overexpression of UBE2C was detected in 73% (11/15) of esophageal adenocarcinomas relative to Barrett’s metaplasia. Tissue microarray showed significant expression of UBE2C in 87% (58/67) of tumors and 70% (7/10) of dysplastic samples but not in the eight metaplastic samples. In addition, highly expressed UBE2C was also observed in 88% (7/8) of lymph node metastases. Abundant UBE2C expression was also found in all four esophageal adenocarcinomas examined as compared to normal and Barrett’s samples using Western blot analysis. Transfection of dominant-negative UBE2C into esophageal adenocarcinoma-derived and UBE2C expressing Seg-1 cells significantly decreased cell proliferation (P = 0.04) and increased mitotic arrest as compared to vector controls (63.5% versus 6.8%, P < 0.001) consistent with the known mechanism of action which is to inhibit progression to anaphase. Silencing the UBE2C gene in Seg-1 cells by transfecting gene specific small interfering RNA (siRNA) caused decrease of cell proliferation and distortion of the cell cycle. Maximal increase of G2 cells (175% of mock cells) was observed after 72 hours of UBE2C silencing. Interestingly, S phase cells were sharply increased (308% of mock cells) within 24 hours after siRNA-mediated silencing of UBE2C expression. Proliferation of Seg-1 cells was also significantly decreased after Seg-1 cells were treated with the proteasome inhibitor MG-262 (1 nM - 1 µM) (P = 0.02). Since UBE2C is abundantly expressed in esophageal adenocarcinomas and adenocarcinoma cell lines expressing UBE2C are sensitive to treatment with MG-262 as well as dominant-negative and siRNA-mediated silencing of UBE2C, patients with esophageal adenocarcinomas that express high levels of UBE2C may benefit from agents targeting this ubiquitin-conjugating enzyme.