Tumor-Secreted GRP78 Facilitates the Migration of Macrophages into Tumors by Promoting Cytoskeleton Remodeling

Abstract

Glucose-regulated protein 78 (GRP78), an important molecular chaperone in the endoplasmic reticulum, is often over-expressed in the central region of advanced tumor and acts as a promoter of tumor progression. As main immune cells in the tumor microenvironment, infiltration of abundant macrophages into advanced tumor further facilitates growth of tumor. Although the potential association between GRP78 and infiltration of macrophages, its underlying mechanisms are poorly understood. Here, we reported that the level of secreted GRP78 was positively correlated with the malignant degree of tumor; and enhanced secretion of GRP78 facilitated recruitment of macrophages into tumors both in vitro and in vivo. Further studies revealed that secreted GRP78 was able to transport into macrophages and bound to intracellular Ca2 , which led to uneven distribution of Ca2 and subsequent polarization of macrophages. Furthermore, macrophages polarization promoted pro-adhesion by activating Fibronectin−integrin-β1−FAK pathway and accelerated MMP2/9 mediated extracellular matrix degradation that contributed to migration of macrophages. Polarization of macrophages also led to the distribution of GTP-Rac1 and GTP-Cdc42 in front protrusion and GTP-RhoA in rear contraction by activating RhoGTPase family members, which further resulted in migration of macrophages in a certain direction. Mechanistically, GRP78-mediated polarization of macrophages activated expression of microRNA-200b-3p. By directly targeting RhoGDI, miR-200b-3p stimulated the activity of RhoGTPase that facilitated cytoskeleton remodeling and subsequently polarization of macrophages. Together, our results reveal a novel function of GRP78 to promote the recruitment of macrophages to tumor and provide a potential therapeutic target for malignancies. Funding Statement: This work was supported by the National Natural Science Foundation of China (No. 31770382 and No. 81803791), “1331 project” Collaborative Innovation Center and team (1331 CIC). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: All animal experiments conducted in this study were approved by the Institutional Animal Care and Use Committee of Shanxi University (Taiyuan, China). All of the experimental procedures were performed in accordance with the protocols and ethical regulations approved by the Institutional Animal Care and Use Committee of Shanxi University (Taiyuan, China).