Targeting ribonucleotide reductase M2 subunit by small interfering RNA exerts anti-oncogenic effects in gastric adenocarcinoma.

Ribonucleotide reductase M2 subunit (RRM2) is one of the two subunits of human ribonucleotide reductase which plays a critical role in tumor progression. The aim of the present study was to analyze its expression, clinical significance and biological functions in gastric adenocarcinoma. We observed the upregulation of RRM2 mRNA and protein in all nine gastric cancer cell lines examined. In paired primary gastric cancers, both mRNA and protein levels of RRM2 were significantly upregulated in tumors compared with the corresponding non-tumorous gastric tissues. RRM2 protein expression correlated with higher tumor grade, advanced T stage and poor disease-specific survival. RRM2 knockdown in gastric cancer cell lines AGS, MKN1 and MKN28 significantly suppressed cell proliferation, inhibited monolayer colony formation, reduced cell invasion and induced apoptosis. Downregulation of RRM2 suppressed xenograft formation in vivo. Collectively, these findings suggest that RRM2 plays a crucial role in gastric tumorigenesis and may serve as a potential prognostic marker and therapeutic target in gastric cancer.

Yin Yang 1 contributes to gastric carcinogenesis and its nuclear expression correlates with shorter survival in patients with early stage gastric adenocarcinoma.

BACKGROUND: Yin Yang 1 (YY1) is a transcription factor that regulates diverse biological processes and increasing recognized to have important roles in carcinogenesis. The function and clinical significance of YY1 in gastric adenocarcinoma (GAC) have not been elucidated. METHODS: In this study, the functional role of YY1 in gastric cancer was investigated by MTT proliferation assays, monolayer colony formation, cell cycle analysis, signaling pathway analysis, Western blot analysis and in vivo study through YY1 knockdown or overexpression. Immunohistochemical study with YY1 antibody was performed on tissue microarray consisting of 247 clinical GAC samples. The clinical correlation and prognosis significance were evaluated. RESULTS: YY1 expression was up-regulated in gastric cancer cell lines and primary gastric cancers. Knocking down YY1 by siYY1 inhibited cell growth, inducing G1 phase accumulation and apoptosis. Ectopic YY1 expression enhanced cell proliferation in vitro and in vivo. Knocking down YY1 in gastric cancer cells suppressed proliferation by inhibiting Wnt/ß-catenin pathway, whereas its overexpression exerted oncogenic property by activating Wnt/ß-catenin pathway. In primary GAC samples, YY1 nuclear expression correlated with shorter survival and predicted poor prognosis in early stage GACs. CONCLUSION: Our data demonstrated that YY1 contributes to gastric carcinogenesis in gastric cancer. In early stage GACs YY1 might serve as a poor prognostic marker and possibly as a potential therapeutic target.

Characterization of rare transforming KRAS mutations in sporadic colorectal cancer.

KRAS mutational status has been shown to be a predictive biomarker of resistance to anti-EGFR monoclonal antibody (mAb) therapy in patients with metastatic colorectal cancer. We report the spectrum of KRAS mutation in 1506 patients with colorectal cancer and the identification and characterization of rare insertion mutations within the functional domain of KRAS. KRAS mutations are found in 44.5% (670/1506) of the patients. Two cases are found to harbor double mutations involving both codons 12 and 13. The frequencies of KRAS mutations at its codons 12, 13, 61, and 146 are 75.1%, 19.3%, 2.5%, and 2.7%, respectively. The most abundant mutation of codon 12 is G12D, followed by G12V and G12C while G13D is the predominant mutation in codon 13. Mutations in other codons are rare. The KRAS mutation rate is significantly higher in women (48%, 296/617) than in men (42.1%, 374/889, P = 0.023). Tumors on the right colon have a higher frequency of KRAS mutations than those on the left (57.3% vs. 40.4%, P<0.0001). Two in-frame insertion mutations affect the phosphate-binding loop (codon 10-16) of KRAS are identified. One of them has never been reported before. Compared with wild-type protein, the insertion variants enhance the cellular accumulation of active RAS (RAS-GTP) and constitutively activate the downstream signaling pathway. NIH3T3 cells transfected with the insertion variants show enhanced anchorage-independent growth and in vivo tumorigenicity. Potentially these mutations contribute to primary resistance to anti-EGFR mAb therapy but the clinical implication requires further validation.