p27T187A knockin identifies Skp2/Cks1 pocket inhibitors for advanced prostate cancer

Abstract

SCFSkp2/Cks1 ubiquitinates Thr187-phosphorylated p27 for degradation. Over-expression of Skp2 coupled with under-expression 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 down-regulation. 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.

Skp2 deficiency restricts the progression and stem cell features of castration-resistant prostate cancer by destabilizing Twist

“…Future animal studies are needed to determine whether Skp2 inhibition can counteract the CRPC progression by Pten/p53 co-inactivation and or other oncogenic insults. Our study together with previous reports 45 – 47 suggest that Skp2 inhibitors can be promising therapeutics not only for treatment-naïve but also CRPC.…”

“… 53 Among these inhibitors, cpd C1 was further characterized for its efficacy in targeting the growth of CRPC organoids. 45 Cpd A was identified through an in vitro Skp2-mediated p27 ubiquitination assay. Cpd A blocks the recruitment of Skp2 to the SCF ligase complex for inhibiting Skp2 functions.…”

The Cks1/Cks2 axis fine-tunes Mll1 expression and is crucial for MLL-rearranged leukaemia cell viability

“…The SCF Skp2-Cks1 complex is one constituent of the Cullin-RING ligase family, specifically targeting a small range of proteins within the larger range of pan-Cullin mediated degradation [89] , [90] , [91] . The new generation of inhibitors targeting the SCF SKP2-CKS1 complex provides a more specific and sensitive treatment, which may reduce off-target effects [57] , [58] , [92] . Currently, therapies targeting epigenetic functions of MLL-FPs, including BET [70] , [71] , [93] and DOT1L [94] inhibitors, produce satisfactory results initially, but resistance emerges due to transcriptional plasticity [70] , [71] , [95] , [96] .…”

Identification of highly penetrant Rb-related synthetic lethal interactions in triple negative breast cancer

“…As well as targeting Rb-defective TNBC, the potential for using SKP2 inhibition in other cancer histologies associated with Rb defects is considerable. For example, the hyper-proliferative phenotype of Rb -depleted human retinoblastoma cells and mouse melanotrophs is dependent upon the SKP2 [ 48 , 62 ] and the SKP2/CKS1 pocket inhibitor, SKPinC1, inhibits Rb/p53 -defective mouse prostate tumour cell organoids [ 63 ]. Finally, large-scale shRNA screens in TCLs from a variety of cancer histologies (and our analysis described in Fig.…”