Priority Research Papers:
Identification of Smurf2 as a HIF-1α degrading E3 ubiquitin ligase
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Shuai Zhao1,2,4,5 and Wafik S. El-Deiry1,2,3,4,5,6
1 Laboratory of Translational Oncology and Experimental Cancer Therapeutics, Warren Alpert Medical School, Brown University, Providence, RI, USA
2 Pathobiology Graduate Program, Brown University, Providence, RI, USA
3 Department of Pathology and Laboratory Medicine, Brown University, Providence, RI, USA
4 Joint Program in Cancer Biology, Brown University and Lifespan Cancer Institute, Providence, RI, USA
5 Cancer Center at Brown University, Warren Alpert Medical School, Brown University, Providence, RI, USA
6 Hematology/Oncology Division, Lifespan Cancer Institute, Providence, RI, USA
|Wafik S. El-Deiry,||email:||[email protected]|
Keywords: Smurf2; CDK4/6 inhibition; HIF1alpha; hypoxia; cancer therapy
Received: September 03, 2021 Accepted: September 09, 2021 Published: September 28, 2021
The major adaptive response to hypoxia involves hypoxia-inducible factor HIF-1α which is regulated by von Hippel Lindau (VHL) E3 ligase. We previously observed a stabilization of HIF-1α by cyclin-dependent kinases CDK1 and CDK4/6 that is independent of VHL, hypoxia or p53, and found that CDK4/6 inhibitors destabilize HIF-1α under normoxia and hypoxia. To further investigate the molecular mechanism of HIF-1α destabilization by CDK1 or CDK4/6 inhibitors, we performed a proteomic screen on immunoprecipitated HIF-1α from hypoxic colorectal cancer cells that were either untreated or treated with CDK1 inhibitor Ro3306 and CDK4/6 inhibitor palbociclib. Our proteomics screen identified a number of candidates that were enriched in palbociclib-treated hypoxic cells including SMAD specific E3 ubiquitin protein ligase 2 (Smurf2). We also identified a HIF-1α peptide that appeared to be differentially phosphorylated after palbociclib treatment. Gene knockdown of SMURF2 increased basal expression of HIF-1α even in the presence of Ro3306 or two different CDK4/6 inhibitors, palbociclib and abemaciclib. Overexpression of Smurf2 inhibited expression of HIF-1α and enhanced HIF-1α ubiquitination in normoxia. Proteasome inhibitor MG-132 partially rescued HIF-1α expression when Smurf2 was overexpressed. Smurf2 overexpression also inhibited HIF-1α expression level in two other cell lines, SW480 and VHL-deficient RCC4. Overexpression of SMURF2 mRNA is correlated with improved disease-free survival and overall survival in clear cell renal cell cancer. Our results unravel a previously unknown mechanism involving Smurf2 for HIF-1α destabilization in CDK4/6 inhibitor-treated cells, thereby shedding light on VHL-independent HIF-1α regulation.
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