Hypoxia-Inducible Factor 1 Is Activated by Dysregulated Cyclin E during Mammary Epithelial Morphogenesis

Abstract

Increased cyclin E expression has been identified in human tumors of diverse histologies, and in studies of primary breast cancers, high cyclin E is associated with poor prognosis. We have studied dysregulated cyclin E in epithelial tissues using organotypic cultures of human mammary epithelial cells and a murine model. We unexpectedly discovered that dysregulated cyclin E impairs normal acinar morphogenesis in vitro, and this is associated with the induction of p21^Cip1, p27^Kip1, and cellular senescence. Cyclin E-induced morphogenesis arrest is dependent upon hypoxia-inducible factor 1α (HIF-1α), which itself is induced by high cyclin E both in cultured mammary acini and in mammary epithelial tissues in a mouse model of deregulated cyclin E expression. We next determined that E2F activity directly regulates and is required for induction of HIF1A by cyclin E. Additionally, we found that cyclin E deregulation in mammary acini decreases, in an E2F-independent manner, expression of the EGLN1 prolyl hydroxylase that regulates HIF-1α degradation within the VHL ubiquitin ligase pathway. Together, our findings reveal a direct link between cyclin E and HIF-1 activities in mammary epithelial cells and implicate HIF-1 as a mediator of proliferation-independent phenotypes associated with high cyclin E expression in some human breast cancers.

ACKNOWLEDGMENTS

We thank Joan Brugge and her laboratory (Harvard Medical School) for providing instruction in organotypic mammary epithelial cell cultures, with support from the National Cancer Institute. Navdeep Chandel (Northwestern University) provided reagents and expert advice.

This work was supported by NIH grants K22CA130984 (A.C.M.) and R01CA102742 (B.E.C.), as well as funding from the Schweppe and Zell Family Foundations (to A.C.M.).