A Novel CXCR3-B Chemokine Receptor-induced Growth-inhibitory Signal in Cancer Cells Is Mediated through the Regulation of Bach-1 Protein and Nrf2 Protein Nuclear Translocation

Abstract

Chemokines and their receptors play diverse roles in regulating cancer growth and progression. The receptor CXCR3 can have two splice variants with opposite functions. CXCR3-A promotes cell growth, whereas CXCR3-B mediates growth-inhibitory signals. However, the negative signals through CXCR3-B in cancer cells are not well characterized. In this study, we found that CXCR3-B-mediated signaling in MCF-7 and T47D breast cancer cells induced apoptotic cell death. Signals through CXCR3-B decreased the levels of the antiapoptotic proteins Bcl-2 and Bcl-xL and increased the expression of apoptotic cleaved poly(ADP-ribose) polymerase. Along with up-regulation in apoptosis, CXCR3-B signals were associated with a decrease in cellular autophagy with reduced levels of the autophagic markers Beclin-1 and LC3B. Notably, CXCR3-B down-regulated the expression of the cytoprotective and antiapoptotic molecule heme oxygenase-1 (HO-1) at the transcriptional level. There was an increased nuclear localization of Bach-1 and nuclear export of Nrf2, which are important negative and positive transcription factors, respectively, for HO-1 expression. We also observed that CXCR3-B promoted the activation of p38 MAPK and the inhibition of ERK-1/2. CXCR3-B could not induce cancer cell apoptosis at the optimal level when we either inhibited p38 activity or knocked down Bach-1. Further, CXCR3-B-induced apoptosis was down-regulated when we overexpressed HO-1. Together, our data suggest that CXCR3-B mediates a growth-inhibitory signal in breast cancer cells through the modulations of nuclear translocation of Bach-1 and Nrf2 and down-regulation of HO-1. We suggest that the induction of CXCR3-B-mediated signaling can serve as a novel therapeutic approach where the goal is to promote tumor cell apoptosis.