Reduced Expression of Mismatch Repair Genes MSH6/MSH2 Directly Promotes Pituitary Tumor Growth via the ATR-Chk1 Pathway.

Context: The mechanisms of pituitary adenoma (PA) pathogenesis and proliferation remain largely unknown. Objectives: To clarify the role of mismatch repair (MMR) genes in the molecular mechanism of PA proliferation. Design: We performed quantitative analyses by real-time polymerase chain reaction and immunohistochemistry to detect MMR gene and protein expression in human PAs (n = 47). We also performed correlation analyses of expression levels and tumor volume doubling time (TVDT; n = 31). Specifically, correlation analyses were performed between genes with significant correlation and ataxiatelangiectasia and Rad3-related (ATR) expression in cell-cycle regulatory mechanism ATR-checkpoint kinase 1 (Chk1) pathway (n = 93). We investigated the effect of reduced gene expression on cell proliferation and ATR gene expression in AtT-20ins cells and primary cultures of human PAs. Results: Expression of mutS homologs 6 and 2 (MSH6 and MSH2) was positively associated with TVDT (R = 0.52, P = 0.003, and R = 0.44, P = 0.01), as were the corresponding protein levels. Gene expression was positively associated with ATR expression (R = 0.47, P < 0.00001, and R = 0.49, P < 0.00001). In AtT-20ins, the reduction of MSH6 and/or MSH2 expression by small interfering RNA significantly promoted cell proliferation by decreasing ATR expression. This effect was also observed in primary culture. Conclusion: Reduction of MSH6 and MSH2 expression at the messenger RNA and protein levels could be involved in direct PA proliferation by promoting cell-cycle progression or decreasing the rate of apoptosis through interference with the function of the ATR-Chk1 pathway.