MAPK8 and prostate intraepithelial neoplasia: Further studies also found that in the region where PIN occurs, PIN cells can recruit macrophages to gather by secreting ICAM-1 and CCL2, while recruited macrophages can activate ERK and JNK signals in PIN cells by secreting C5a, CXCL1, and CCL2 to promote the proliferation of PIN cells (90).