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.