CCI-779 Inhibits Cell-Cycle G2–M Progression and Invasion of Castration-Resistant Prostate Cancer via Attenuation of UBE2C Transcription and mRNA Stability

Abstract

The cell-cycle G2/M phase gene UBE2C is over-expressed in various solid tumors including castration-resistant prostate cancer (CRPC). Our recent studies found UBE2C to be a CRPC-specific androgen receptor (AR) target gene that is necessary for CRPC growth, providing a potential novel target for therapeutic intervention. Here we demonstrate that the G1/S cell-cycle inhibitor-779 (CCI-779), an mTOR inhibitor, inhibited UBE2C mRNA and protein expression in AR-positive CRPC cell models abl and C4-2B. Treatment with CCI-779 significantly decreased abl cell proliferation in vitro and in vivo through inhibition of cell-cycle progression of both G2/M and G1/S phases. In addition, exposure of abl and C4-2B cells to CCI-779 also decreased UBE2C-dependent cell invasion. The molecular mechanisms for CCI-779 inhibition of UBE2C gene expression involved a decreased binding of AR co-activators SRC1, SRC3, p300 and MED1 to the UBE2C enhancers, leading to a reduction in RNA polymerase II loading to the UBE2C promoter, and attenuation of UBE2C mRNA stability. Our data suggest that, in addition to its ability to block cell-cycle G1/S transition, CCI-779 causes a cell-cycle G2/M accumulation and an inhibition of cell invasion through a novel UBE2C-dependent mechanism, which contributes to anti-tumor activities of CCI-779 in UBE2C over-expressed AR-positive CRPC.

Definition of a FoxA1 Cistrome That Is Crucial for G1 to S-Phase Cell-Cycle Transit in Castration-Resistant Prostate Cancer

“…S1A), another CRPC cell model (26). We next examined the effect of FoxA1 silencing on CRPC cell-cycle progression using a thymidine-nocodazole block in order to enrich abl cells at mitosis (15). Consistent with the role of FoxA1 in the upregulation of cell-cycle G2-M phase genes in CRPC cells (11), FoxA1 silencing caused a G2-M accumulation in the treated abl cells (Fig.…”

“…Cell proliferation was measured using the WST-1 kit (Roche, Indianapolis, IN) as previously described (15). …”

“…Cells were collected, and DNA contents were analyzed by a FACS Calibur cell flow cytometer (Becton Dickinson Biosciences, San Diego, CA) as previously described (14, 15). …”

Dissecting Major Signaling Pathways throughout the Development of Prostate Cancer

“…These binding sites might be close to the target genes or acting as distal enhancers. During PCa progression, many androgen-regulated genes including UBE2C, CND1, p21, and p27 are up-regulated [43, 44]. In most of CRPCa conditions, where AR overexpression is found, prostate cells show more sensitivity to lower concentrations of the ligand [45].…”

Androgen Deprivation Therapy as Primary Treatment for Prostate Cancer

“…In addition, the AR has been shown to regulate a distinct transcription program in androgen-independent PCa, and newer therapies are being developed that target these downstream target genes involved in CRPC growth (30).…”