AbstractChemerin (RARRES2) is an endogenous leukocyte chemoattractant known to recruit innate immune cells through its chemotactic receptor, CMKLR1. RARRES2 is often downregulated in prostate cancer and across multiple tumor types compared to normal tissue. Additionally, a methylome-wide analysis identified RARRES2 as one of the most hypermethylated genes in sarcoma. Recent studies have shown that augmenting chemerin in the tumor microenvironment significantly suppresses tumor growth, at least in part by recruitment of immune effector cells. However, as tumor cells have been shown to express functional chemokine receptors that can impact their phenotype, we hypothesized that chemerin might have additional, tumor-intrinsic effects. Here, we show for the first time that human cancer cells exposed to exogenous chemerin significantly upregulate PTEN expression and activity. Additionally, chemerin-induced PTEN expression correlated with a concomitant reduction in PD-L1 mRNA and protein expression. Chemerin treatment of tumor cells led to significantly reduced tumor cell migration/invasion, as well as significantly increased cytotoxicity by T cells. siRNA knockdown of tumor expressed CMKLR1 abrogated chemerin-induced modulation of PTEN and PD-L1 expression and activity, supporting the presence of a CMKLR1/PTEN/PD-L1 signaling cascade. We then compared chemerin treatment to PD-L1 inhibition by siRNA knockdown or the antagonistic antibody atezolizumab in T cell cytotoxicity assays and surprisingly found chemerin treatment was as effective as both PD-L1 knockdown and atezolizumab treatment in mediating tumor lysis. Collectively, our data show a novel link between chemerin, PTEN and PD-L1 in human tumor lines, with functional consequences that may have a role in improving T cell-mediated immunotherapies.
Apoptotic effects of signal transduction inhibitors on human tumor cells with different PTEN expression