Transcriptional Repression of CCL2 by K3.1 K Channel Activation and LRRC8A Anion Channel Inhibition in THP-1-Differentiated M Macrophages.

We investigated the role of the intermediate-conductance, Ca-activated K channel K3.1 and volume-regulatory anion channel LRRC8A in regulating C-C motif chemokine ligand 2 (CCL2) expression in THP-1-differentiated M macrophages (M-MACs), which serve as a useful model for studying tumor-associated macrophages (TAMs). CCL2 is a potent chemoattractant involved in the recruitment of immunosuppressive cells and its expression is regulated through intracellular signaling pathways such as ERK, JNK, and Nrf2 in various types of cells including macrophages. The transcriptional expression of CCL2 was suppressed in M-MACs following treatment with a K3.1 activator or an LRRC8A inhibitor via distinct signaling pathways: ERK-CREB2 and JNK-c-Jun pathways for K3.1, and the NOX2-Nrf2-CEBPB pathway for LRRC8A. Under in vitro conditions mimicking the elevated extracellular K concentration ([K]) characteristic of the tumor microenvironment (TME), CCL2 expression was markedly upregulated, and this increase was reversed by treatment with them in M-MACs. Additionally, the WNK1-AMPK pathway was, at least in part, involved in the high [K]-induced upregulation of CCL2. Collectively, modulating K3.1 and LRRC8A activities offers a promising strategy to suppress CCL2 secretion in TAMs, potentially limiting the CCL2-induced infiltration of immunosuppressive cells (TAMs, Ts, and MDSCs) in the TME.