Critical Role for Histone Deacetylase 6 (HDAC6) in the Regulation of IL-6, and the JAK/STA3 Signaling Cascade in Macrophages

Histone Deacetylases (HDACs) have divergent effects over the production of anti- and pro-inflammatory cytokines in Antigen Presenting Cells (APCs). We have previously shown that modulation of specific HDACs can alter the immunogenicity of APCs, either to an activating or tolerogenic phenotype. We recently identified HDAC6 to positively regulate IL-10 production. However, the participation of this HDAC in other immune related cellular processes remains unknown. In this work we are presenting evidence of the important role of HDAC6 in the regulation of IL-6 via activation of the JAK/STAT3 pathway.

Stable knockdown clones of HDAC6 (KDHDAC6) and Non-target (NT) cells were generated in RAW264.7 murine macrophages using lentiviral shRNA for HDAC6 or non-target (NT) respectively. Two KDHADC6 and two NT clones were treated with LPS or untreated and then analyzed by microarray using the Affymetrix GeneChip Mouse 430 2.0. Significantly down- or up-regulated genes were analyzed by their ontology distribution and selected genes were validated by quantitative real-time RT-PCR, ELISA, or immunoblots. Additionally, changes in the expression of these selected genes were tested in cells treated with selective HDAC6 inhibitors.

1542 genes were down-regulated and 775 up-regulated in KDHDAC6 cells. Their ontology distribution revealed significant changes in immune-related (632) and apoptosis/cell cycle control (47) genes. Importantly, IL-6 was one of the most highly down-regulated genes in KDHDAC6 cells. Therefore, we next analyzed the relevance of these findings by studying the tolerogenic JAK/STAT3 signaling pathway which is known to be activated by IL-6 and critical in the final outcome of APCs in response to stimuli. We observed a complete abrogation in the phosphorylation of JAK2 and STAT3 proteins in KDHDAC6 cells in response to LPS, which was reverted when these cells were treated with exogenous IL-6.

These results demonstrate the requirement of HDAC6 in the production of IL-6 in response to LPS, and therefore positions this deacetylase as an important regulator of the JAK/STAT3 pathway. These findings provide insight into the molecular mechanisms controlling the immunogenicity of APCs, supporting the use of HDAC6 inhibitors to enhance immune activation.

No relevant conflicts of interest to declare.