Varun Sasidharan Nair1, Salman M Toor1, Bassam R Ali2, Eyad Elkord1,3. 1. a Cancer Research Center , Qatar Biomedical Research Institute, College of Science and Engineering, Hamad Bin Khalifa University, Qatar Foundation , Doha , Qatar. 2. b College of Medicine and Health Sciences , United Arab Emirates University , Al Ain , United Arab Emirates. 3. c Institute of Cancer Sciences , University of Manchester , Manchester , UK.
Abstract
OBJECTIVES: Breast cancer is the most commonly diagnosed cancer, and it is a leading cause of cancer-related deaths in females worldwide. Triple-negative breast cancer (TNBC) constitutes 15% of breast cancer and shows distinct metastasis profiles with poor prognosis. Strong PD-L1 expression has been observed in some tumors, supporting their escape from immune surveillance. Targeting PD-L1 could be a promising therapeutic approach in breast cancer patients. We investigated potential molecular mechanisms for constitutive expression of PD-L1 by inhibiting upstream STAT1 and STAT3 signals. METHODS: PD-L1 expression in three breast cancer cell lines was measured using quantitative PCR and western blotting. Activation of STAT1 and STAT3 was blocked using pharmacological inhibitors and siRNA. The mechanism underlying the constitutive expression of PD-L1 was investigated using ChIP and co-immunoprecipitation assays. RESULTS: We found that individual inhibition of STAT1 and STAT3 activation partially downregulated PD-L1, while combined inhibition completely downregulated PD-L1 expression. Moreover, our results suggest that pSTAT1-pSTAT3 dimerize in cytosol and translocate to the nucleus, where they bind to PD-L1 promoter and induce PD-L1 expression. CONCLUSION: These findings provide a rationale for combined targeting of STAT1 and STAT3 for the development of immune-based cancer therapies for down regulation of PD-L1 expression.
OBJECTIVES:Breast cancer is the most commonly diagnosed cancer, and it is a leading cause of cancer-related deaths in females worldwide. Triple-negative breast cancer (TNBC) constitutes 15% of breast cancer and shows distinct metastasis profiles with poor prognosis. Strong PD-L1 expression has been observed in some tumors, supporting their escape from immune surveillance. Targeting PD-L1 could be a promising therapeutic approach in breast cancerpatients. We investigated potential molecular mechanisms for constitutive expression of PD-L1 by inhibiting upstream STAT1 and STAT3 signals. METHODS:PD-L1 expression in three breast cancer cell lines was measured using quantitative PCR and western blotting. Activation of STAT1 and STAT3 was blocked using pharmacological inhibitors and siRNA. The mechanism underlying the constitutive expression of PD-L1 was investigated using ChIP and co-immunoprecipitation assays. RESULTS: We found that individual inhibition of STAT1 and STAT3 activation partially downregulated PD-L1, while combined inhibition completely downregulated PD-L1 expression. Moreover, our results suggest that pSTAT1-pSTAT3 dimerize in cytosol and translocate to the nucleus, where they bind to PD-L1 promoter and induce PD-L1 expression. CONCLUSION: These findings provide a rationale for combined targeting of STAT1 and STAT3 for the development of immune-based cancer therapies for down regulation of PD-L1 expression.
Entities:
Keywords:
Breast cancer; PD-L1; STAT1; STAT3; triple-negative breast cancer
Authors: Li Li; Jun Zhang; Juan Chen; Zijun Y Xu-Monette; Yi Miao; Min Xiao; Ken H Young; Sa Wang; L Jeffrey Medeiros; Michael Wang; Richard J Ford; Lan V Pham Journal: Blood Date: 2018-09-12 Impact factor: 22.113