Sanjeev Kumar Srivastava1,2, Mohammad Aslam Khan1,2, Shashi Anand1,2, Haseeb Zubair1,2, Sachin Kumar Deshmukh1,2, Girijesh Kumar Patel1,2, Seema Singh1,2,3, Joel Andrews4, Bin Wang5, James Elliot Carter1, Ajay Pratap Singh6,7,8. 1. Department of Pathology, College of Medicine, University of South Alabama, Mobile, AL, 36617, USA. 2. Cancer Biology Program, Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA. 3. Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile, AL, 36688, USA. 4. Bioimaging Core Facility, Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA. 5. Department of Mathematics and Statistics, University of South Alabama, Mobile, AL, 36688, USA. 6. Department of Pathology, College of Medicine, University of South Alabama, Mobile, AL, 36617, USA. asingh@southalabama.edu. 7. Cancer Biology Program, Mitchell Cancer Institute, University of South Alabama, Mobile, AL, 36604, USA. asingh@southalabama.edu. 8. Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, Mobile, AL, 36688, USA. asingh@southalabama.edu.
Abstract
BACKGROUND: Aberrant activation of androgen receptor signalling following castration therapy is a common clinical observation in prostate cancer (PCa). Earlier, we demonstrated the role of MYB overexpression in androgen-depletion resistance and PCa aggressiveness. Here, we investigated MYB-androgen receptor (AR) crosstalk and its functional significance. METHODS: Interaction and co-localization of MYB and AR were examined by co-immunoprecipitation and immunofluorescence analyses, respectively. Protein levels were measured by immunoblot analysis and enzyme-linked immunosorbent assay. The role of MYB in ligand-independent AR transcriptional activity and combinatorial gene regulation was studied by promoter-reporter and chromatin immunoprecipitation assays. The functional significance of MYB in castration resistance was determined using an orthotopic mouse model. RESULTS: MYB and AR interact and co-localize in the PCa cells. MYB-overexpressing PCa cells retain AR in the nucleus even when cultured under androgen-deprived conditions. AR transcriptional activity is also sustained in MYB-overexpressing cells in the absence of androgens. MYB binds and promotes AR occupancy to the KLK3 promoter. MYB-overexpressing PCa cells exhibit greater tumorigenicity when implanted orthotopically and quickly regain growth following castration leading to shorter mice survival, compared to those carrying low-MYB-expressing prostate tumours. CONCLUSIONS: Our findings reveal a novel MYB-AR crosstalk in PCa and establish its role in castration resistance.
BACKGROUND: Aberrant activation of androgen receptor signalling following castration therapy is a common clinical observation in prostate cancer (PCa). Earlier, we demonstrated the role of MYB overexpression in androgen-depletion resistance and PCa aggressiveness. Here, we investigated MYB-androgen receptor (AR) crosstalk and its functional significance. METHODS: Interaction and co-localization of MYB and AR were examined by co-immunoprecipitation and immunofluorescence analyses, respectively. Protein levels were measured by immunoblot analysis and enzyme-linked immunosorbent assay. The role of MYB in ligand-independent AR transcriptional activity and combinatorial gene regulation was studied by promoter-reporter and chromatin immunoprecipitation assays. The functional significance of MYB in castration resistance was determined using an orthotopic mouse model. RESULTS: MYB and AR interact and co-localize in the PCa cells. MYB-overexpressing PCa cells retain AR in the nucleus even when cultured under androgen-deprived conditions. AR transcriptional activity is also sustained in MYB-overexpressing cells in the absence of androgens. MYB binds and promotes AR occupancy to the KLK3 promoter. MYB-overexpressing PCa cells exhibit greater tumorigenicity when implanted orthotopically and quickly regain growth following castration leading to shorter mice survival, compared to those carrying low-MYB-expressing prostate tumours. CONCLUSIONS: Our findings reveal a novel MYB-AR crosstalk in PCa and establish its role in castration resistance.
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Authors: Arun Bhardwaj; Sanjeev K Srivastava; Seema Singh; Sumit Arora; Nikhil Tyagi; Joel Andrews; Steven McClellan; James E Carter; Ajay P Singh Journal: Oncotarget Date: 2014-11-30