Abstract
The epithelium-specific Ets transcription factor, SPDEF, plays a critical role in metastasis of prostate and breast cancer cells. While enhanced SPDEF expression blocks migration and invasion, knockdown of SPDEF expression enhances migration, invasion, and metastasis of cancer cells. SPDEF expression and activation is tightly regulated in cancer cells; however, the precise mechanism of SPDEF regulation has not been explored in detail. In this study we provide evidence that the cell cycle kinase CDK11p58, a protein involved in G2/M transition and degradation of several transcription factors, directly interacts with and phosphorylates SPDEF on serine residues, leading to subsequent ubiquitination and degradation of SPDEF through the proteasome pathway. As a consequence of CDK11p58 mediated degradation of SPDEF, this loss of SPDEF protein results in increased prostate cancer cell migration and invasion. In contrast, knockdown of CDK11p58 protein expression by interfering RNA or SPDEF overexpression inhibit migration and invasion of cancer cells. We demonstrate that CDK11p58 mediated degradation of SPDEF is attenuated by Growth Arrest and DNA damage-inducible 45 (GADD45) α and, two proteins inducing G2/M cell cycle arrest. We show that GADD45 α and γ, directly interact with CDK11p58 and thereby inhibit CDK11p58 activity, and consequentially SPDEF phosphorylation and degradation, ultimately reducing prostate cancer cell migration and invasion. Our findings provide new mechanistic insights into the complex regulation of SPDEF activity linked to cancer metastasis and characterize a previously unidentified SPDEF/CDK11p58/GADD45α/γ pathway that controls SPDEF protein stability and SPDEF-mediated effects on cancer cell migration and invasion.
Highlights
Metastatic prostate cancer lacks any effective therapy, clinical efficacy of the first antimetastatic drug cabozantinib has shown some promise [1]
We previously demonstrated that SPDEF effectively inhibits prostate cancer migration and invasion and may, function as a tumor and metastasis suppressor [5]
We showed that GADD45α and γ induce cell cycle arrest and apoptosis in prostate cancer cells, and NFκB- as well as JunD-mediated repression of GADD45α and γ are essential for prostate cancer cells to escape cell death [17, 18]
Summary
Metastatic prostate cancer lacks any effective therapy, clinical efficacy of the first antimetastatic drug cabozantinib has shown some promise [1]. The potential role of the non-fusion epithelial-specific Ets factor, SPDEF, as prostate cancer tumor and metastasis suppressor recently emerged, demonstrating that SPDEF expression loss in advanced prostate cancer correlates with poor outcome [5,6,7,8,9,10,11]. We and others have shown that inhibition of SPDEF expression in prostate cancer cells reduces adhesion and increases migration, invasion and EMT, while overexpression prevents these functions indicating a role of SPDEF in prostate cancer metastasis, but with apparent opposite activity to ERG [5, 6, 12]. While we have demonstrated interaction of SPDEF with the androgen receptor (AR) and various other proteins relevant for cancer signalling [5, 16], no studies have been reported as of yet about the precise regulatory mechanisms of SPDEF protein expression and activity in the context of metastasis
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