SCFSkp2/Cks1 ubiquitinates Thr187-phosphorylated p27 for degradation. Overexpression of Skp2 coupled with underexpression of p27 are frequent characteristics of
cancer cells. When the role of SCFSkp2/Cks1-mediated p27 ubiquitination in
cancer was specifically tested by p27 Thr187-to-Ala knockin (p27T187A KI), it was found dispensable for KrasG12D-induced lung
tumorigenesis but essential for Rb1-deficient pituitary
tumorigenesis. Here we identify pRb and p53 doubly deficient (DKO) prostate
tumorigenesis as a context in which p27 ubiquitination by SCFSkp2/Cks1 is required for p27 downregulation. p27
protein accumulated in prostate when p27T187A KI mice underwent DKO prostate
tumorigenesis. p27T187A KI or Skp2 knockdown (KD) induced similar degrees of p27
protein accumulation in DKO prostate cells, and Skp2 KD did not further increase p27
protein in DKO prostate cells that contained p27T187A KI (AADKO prostate cells). p27T187A KI activated an E2F1-p73-apoptosis axis in DKO prostate
tumorigenesis, slowed
disease progression and significantly extended survival. Querying co-occurrence relationships among RB1, TP53, PTEN, NKX3-1 and MYC in TCGA of
prostate cancer identified co-inactivation of RB1 and TP53 as the only statistically significant co-occurrences in metastatic
castration-resistant
prostate cancer (mCRPC). Together, our study identifies Skp2/Cks1 pocket inhibitors as potential
therapeutics for mCRPC. Procedures for establishing mCRPC organoid cultures from contemporary patients were recently established. An Skp2/Cks1 pocket inhibitor preferentially collapsed DKO prostate
tumor organoids over AADKO organoids, which spontaneously disintegrated over time when DKO prostate
tumor organoids grew larger, setting the stage to translate mouse model findings to
precision medicine in the clinic on the organoid platform.