PARP9 is overexpressed in human breast cancer and promotes cancer cell migration

Poly(ADP-Ribose) polymerase family member 9 (PARP9) promotes the proliferation, survival and chemotherapy resistance in lymphoma and prostate cancer. The expression and function of PARP9 in human breast cancer remains unknown. In the present study, it was demonstrated that PARP9 is frequently overexpressed in human breast cancer. In 57 normal breast tissues, the expression of PARP9 was not detected in 43 cases (75.4%), but low levels of PARP9 were detected in 13 cases (22.8%), and modest levels of PARP9 (PARP9/GAPDH ratio ~1:1) were detected in only 1 case (1.7%). In contrast, the expression of PARP9 was detected in all 57 breast cancer tissues, in which the levels of PARP9 were higher than that in paired normal breast tissues. In addition, high levels of PARP9 were detected in 43.8% of breast cancer tissues. Overexpression of PARP9 was negatively associated with estrogen receptor expression, and positively associated with axillary lymph node metastasis. However, PARP9 expression was not associated with other clinicopathological parameters, including age, HER-2 and tumor size. Furthermore, PARP9-knockdown inhibited breast cancer cell migration. These data indicate that PARP9 may promote breast cancer progression.