Reciprocal inhibition of PIN1 and APC/CCDH1 controls timely G1/S transition and creates therapeutic vulnerability.

Cyclin-dependent kinases (CDKs) mediated phosphorylation inactivates the anaphase-promoting complex (APC/CCDH1), an E3 ubiquitin ligase that contains the co-activator CDH1, to promote G1/S transition. PIN1 is a phosphorylation-directed proline isomerase and a master cancer signaling regulator. However, little are known about APC/CCDH1 regulation after phosphorylation and about PIN1 ubiquitin ligases. Here we uncover a domain-oriented reciprocal inhibition that controls the timely G1/S transition: The non-phosphorylated APC/CCDH1 E3 ligase targets PIN1 for degradation in G1 phase, restraining G1/S transition; APC/CCDH1 itself, after phosphorylation by CDKs, is inactivated by PIN1-catalyzed isomerization, promoting G1/S transition. In cancer, PIN1 overexpression and APC/CCDH1 inactivation reinforce each other to promote uncontrolled proliferation and tumorigenesis. Importantly, combined PIN1- and CDK4/6-inhibition reactivates APC/CCDH1 resulting in PIN1 degradation and an insurmountable G1 arrest that translates into synergistic anti-tumor activity against triple-negative breast cancer in vivo. Reciprocal inhibition of PIN1 and APC/CCDH1 is a novel mechanism to control timely G1/S transition that can be harnessed for synergistic anti-cancer therapy.

The association of infectious mononucleosis and invasive breast cancer in The Health of Women (HOW) Study®.

BACKGROUND: The link between Epstein-Barr Virus (EBV) and breast cancer (BC) etiology remains unclear. We utilized the Health of Women (HOW) Study® to understand the association between infectious mononucleosis (IM), a surrogate for EBV infection, and invasive BC. METHODS: The HOW Study® was a web-based survey of BC risk factors with > 40, 000 participants; 183 had IM at < 10 years old, 3, 654 had IM between 10 and 22 years old, 764 had IM at > 22 years old, and 17, 026 never developed IM. Of these 21, 627 women, 2093 had Stages I-III BC and 14, 143 were cancer-free. Binary logistic regression ascertained the association between IM and invasive BC risk by controlling for confounders. RESULTS: A history of IM was associated with a lower likelihood of developing invasive BC compared to women who did not develop IM (adjusted OR = 0.83, 95% CI 0.72-0.94). That finding was driven by women who had IM between 10 and 22 years old (adjusted OR = 0.83, 95% CI 0.72-0.97) albeit no linear association between age at developing IM and breast cancer (p-trend > 0.05). Women who had IM between 10 and 22 years old were less likely to develop estrogen receptor positive (ER+ ; adjusted OR = 0.84, 95% CI 0.71-0.99) or hormone receptor positive (HR+ ; adjusted OR = 0.86, 95% CI 0.73-1.01) BC. There was no association between IM and ER- or HR- BC. CONCLUSION: In the HOW Study®, women diagnosed with IM between the ages of 10 and 22 had a lower risk of developing invasive BC compared to women who never developed IM.