Role of PIP5K1a in human Th17 gene expression
This data was performed as part of Revu et al, "Human IL-17A protein expression is controlled through a PIP5K1a-dependent ARS2 checkpoint". IL-17 secreted by TH17 cells is beneficial for microbial control, but causes inflammation and pathological tissue remodeling in autoimmunity. Hence TH17 differentiation and IL-17 production must be tightly regulated, but to date this has been defined only in terms of transcriptional control.  Phosphatidyinositols are second messengers activated during T cell activation that transduce signals from the TCR and costimulatory receptors at the cell membrane. Here we show phosphatidylinositol(4,5)bisphosphate (PIP2) was unexpectedly enriched in the nucleus of human TH17 cells, dependent on the kinase PIP5K1?, and that blockade of PIP5K1? impaired IL-17A production. In contrast, nuclear PIP2 enrichment was not observed in Th1 or Th2 cells and these subsets did not require PIP5K1? for cytokine production. In multiple sclerosis patient T cells, IL-17 production elicited by myelin basic protein could be inhibited by PIP5K1? blockade. Surprisingly, PIP5K1? blockade did not alter IL17A mRNA levels or stability in TH17 cells. Instead, analysis of PIP5K1?-interacting proteins revealed that PIP5K1? targets ARS2, a nuclear cap binding complex scaffold protein, to facilitate ARS2 binding to IL17A mRNA and subsequent IL-17 protein expression, uncovering a new mechanism for regulating IL-17A protein production and suggesting a novel mechanism of translation control of cytokines. Overall design: Human naïve T cells were isolated and stimulated with anti-CD3, IL-23 and IL-1b for 5 days. On day 3 PIP5K1a inhibitor was added to cultures. On day 5 RNA was isolated and RNA sequencing performed.