p38 MAPK and ERK activation by 9-cis-retinoic acid induces chemokine receptors CCR1 and CCR2 expression in human monocytic THP-1 cells

9-cis-retinoic acid (9CRA) plays an important role in the immune response; this includes cytokine production and cell migration. We have previously demonstrated that 9CRA increases expression of chemokine receptors CCR1 and CCR2 in human monocytes. To better understand how 9CRA induces CCR1 and CCR2 expression, we examined the contribution of signaling proteins in human monocytic THP-1 cells. The mRNA and surface protein up-regulation of CCR1 and CCR2 in 9CRA-stimulated cells were weakly blocked by the pretreatment of SB202190, a p38 MAPK inhibitor, and PD98059, an upstream ERK inhibitor. Activation of p38 MAPK and ERK1/2 was induced in both a time and dose-dependent manner after 9CRA stimulation. Both p38 MAPK and ERK1/2 phosphorylation peaked at 2 h after a 100 nM 9CRA treatment. 9CRA increased calcium influx and chemotactic activity in response to CCR1-dependent chemokines, Lkn-1/CCL15, MIP-1 alpha CCL3, and RANTES/CCL5, and the CCR2-specific chemokine, MCP-1/CCL2. Both SB202190 and PD98059 pretreatment diminished the increased calcium mobilization and chemotactic ability due to 9CRA. SB202190 inhibited the expression and functional activities of CCR1 and CCR2 more effectively than did PD98059. Therefore, our results demonstrate that 9CRA transduces the signal through p38 MAPK and ERK1/2 for CCR1 and CCR2 up-regulation, and may regulate the pro-inflammatory process through the p38 MAPK and ERK-dependent signaling pathways.