Tight Regulation of Diacylglycerol-Mediated Signaling Is Critical for Proper Invariant NKT Cell Development

Abstract

Type I natural killer T (NKT) cells, or iNKT cells, express a semi-invariant T cell receptor characterized by its unique V α 14-Jα 18 usage (iV α 14TCR). Upon interaction with glycolipid/CD1d complexes, the iV α 14TCRs transduce signals that are essential for iNKT selection and maturation. However, it remains unclear how these signals are regulated and how important such regulations are during iNKT development. Diacylglycerol (DAG) is an essential second messenger downstream of the TCR that activates the PKCθ-IKKα/β-NFκB pathway, known to be crucial for iNKT development, as well as the RasGRP1-Ras-Erk1/2 pathway in T cells. DAG kinases (DGKs) play an important role in controlling intracellular DAG concentration and thereby negatively regulate DAG signaling. Here we report that simultaneous absence of DAG kinase α and ζ causes severe defects in iNKT development, coincident with enhanced IKK-NFκB and Ras-Erk1/2 activation. Moreover, constitutive IKKβ and Ras activities also result in iNKT developmental defects. Thus, DAG-mediated signaling is not only essential but also needs to be tightly regulated for proper iNKT cell development.

iNKT cells require TSC1 for terminal maturation and effector lineage fate decisions

“…Tsc1 fl/fl -ERCre + and Tsc1 fl/fl -ERCre -mice were intraperitoneally injected with tamoxifen (100 mg/kg body weight) on days 1, 2, and 5 and then euthanized for experiments on day 8 to delete TSC1 in mature iNKT cells. Splenocytes, thymocytes, LN cells, and liver MNCs were made according to previously published protocols (26,27).…”

“…In T cells, mTOR is activated via the PI3K/AKT and the RASGRP1/RAS/ERK1/2 pathways (24,25). Deficiency and dysregulation of the RASGRP1/RAS/ ERK1/2 pathways impairs iNKT cell development (26,27). mTOR has been found to promote Th differentiation, control regulatory T cell generation and function, inhibit memory CD8 + T cell response, and regulate T cell trafficking in vivo (23,25,(28)(29)(30)(31).…”

Redundant and specialized roles for diacylglycerol kinases α and ζ in the control of T cell functions

“…Loss of either DGKa or DGKz alone does not markedly affect the development of iNKT cells; however, DGKa and DGKz doubly deficient mice show an acute reduction in the number of iNKT cells, with increased cell death and a blockade in the transition from stage 2 (CD44 + NK1.1 − ) to stage 3 (CD44 + NK1.1 + ) (81). Enhanced activation of the RasGRP1-Ras-ERK and PKCq-IKK-NF-kB pathways as a result of a double deficiency in DGKa and DGKz correlates with the defects in the transition from stage 2 to stage 3, as well as in the increased cell death observed in mice bearing constitutively active K-Ras or IKKb, respectively (81). The essential roles for mTORC1 and mTORC2 in the development of the iNKT cell lineage and in the effector functions of these cells (82,83) strengthen the idea of synergy between DGKa and DGKz in the activation of mTOR.…”

“…DAG-mediated Ras activation is important for iNKT cell development, as demonstrated by the substantial decrease in numbers of these cells in RasGRP1-deficient mice (80) and in transgenic mice that express a caDGK (78). Loss of either DGKa or DGKz alone does not markedly affect the development of iNKT cells; however, DGKa and DGKz doubly deficient mice show an acute reduction in the number of iNKT cells, with increased cell death and a blockade in the transition from stage 2 (CD44 + NK1.1 − ) to stage 3 (CD44 + NK1.1 + ) (81). Enhanced activation of the RasGRP1-Ras-ERK and PKCq-IKK-NF-kB pathways as a result of a double deficiency in DGKa and DGKz correlates with the defects in the transition from stage 2 to stage 3, as well as in the increased cell death observed in mice bearing constitutively active K-Ras or IKKb, respectively (81).…”

Rapid Triacylglycerol Turnover in Chlamydomonas reinhardtii Requires a Lipase with Broad Substrate Specificity

“…10, reaction 3), partially preventing the TAG-accumulating phenotype seen in the lipase knockout strains. Second, due to the pleiotropic metabolic, as well as the signaling, functions of DAG, the steady-state DAG amount has to be tightly controlled (47). The action of CrLIP1 in yeast may cause alterations in TAG metabolism by an indirect route involving DAG signaling.…”