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Tumor suppressor SPOP mediates the proteasomal degradation of progesterone receptors (PRs) in breast cancer cells

Progesterone induces proliferation of breast cancer cells and contributes to the development of breast cancer. The effects of progesterone are mediated by progesterone receptors (PRs). However, it is still not fully understood how the proliferative effects of PR is regulated in vivo. Increasing amount of evidence strongly suggests that dysregulation of ubiquitin-proteasome system is closely associated with cancer pathogenesis. Speckle-type POZ protein (SPOP) is an adaptor protein of the CUL3-based E3 ubiquitin ligase complexes. SPOP represents one of the highest loci for loss of heterozygosity (LOH) in breast cancer. SPOP downregulation contributes to breast cancer cell growth and invasion. In this study, we revealed PR as a bona fide substrate for SPOP. SPOP interacts with PR in vivo and targets PR for ubiquitin-dependent proteasomal degradation. Moreover, SPOP suppresses progesteroneinduced PR transactivation, S phase entry, and Erk1/2 activation. Our study revealed novel molecular mechanisms underlying the regulation of PR protein homeostasis in breast cancer cells, and provided insights in understanding the relationship between SPOP inactivation and the development of breast cancer.

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S1705 Progesterone (NSC 9704) Progesterone (NSC 9704, NSC 64377, Pregn-4-ene-3,20-dione) is an endogenous steroid hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. A potent agonist of the nuclear progesterone receptor (nPR) with Kd of 1 nM; An agonist of the membrane progesterone receptors(mPRs); An antagonist of the σ1 receptor. (8) (2)

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