Repeated injection of α-galactosylceramide, a ligand for
iNKT cells, results in long-term unresponsiveness of
iNKT cells, which severely limits its clinical application for cancer therapy. However, the molecular mechanisms leading to
iNKT cells anergy induction remain unclear. We show here that the decreased IFN-γ production and failed tumor rejection observed in anergized
iNKT cells are rescued by deficiency of Cbl-b. Cbl-b was highly expressed in anerzied
iNKT cells and its E3 ligase activity was critical for the down-regulation of IFN-γ.
To clarify how does Cbl-b regulate
iNKT cells’ IFN-γ production, we used human
iNKT cell line and ionomycin treatment as an anergy induction. siRNA experiment indicated that IFN-γ production is also regulated by Cbl-b in ionomycin-induced human
iNKT cell anergy. And NFκB pathway signaling was strongly inhibited in anergized
iNKT cells.
In the search for the substrate of Cbl-b in NFκB pathway signaling molecules, we found that Cbl-b can bind CARMA1 and promote mono-ubiquitination of it. Down-regulation of CARMA1 and Bcl10 complex formation after CD3/28 cross-linking was observed in anergized human
iNKT cells.
This study suggests that Cbl-b-mediated CARMA1 mono-ubiquitination can regulate NFκB pathway signaling and IFN-γ production of
iNKT cells in anergized condition.
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