SYK is activated by mutated MYD88 and drives pro-survival signaling in MYD88 driven B-cell lymphomas

Activating MYD88 mutations promote pro-survival signaling through BTK and HCK, both targets of ibrutinib. Despite high response rates, complete responses to ibrutinib are lacking, and other MYD88 triggered pro-survival pathways may contribute to primary drug resistance. B-cell receptor (BCR) signaling has been observed in lymphomas driven by mutated MYD88, even without activating the BCR pathway mutations. We identified activated SYK (p-SYK), a component of BCR in complex with MYD88 in MYD88-mutated WM and ABC DLBCL lymphoma cells. Confocal microscopy confirmed co-localization of MYD88 with SYK in MYD88-mutated cells. Knockdown of MYD88 or use of a MYD88 signaling inhibitor abrogated SYK activation, while expression of mutated but not wild-type MYD88 amplified p-SYK in MYD88-mutated and wild-type lymphoma cells. Knockdown of SYK or use of inhibitors targeting SYK blocked p-STAT3 and p-AKT signaling in MYD88-mutated cells. Cell viability analysis showed that combining ibrutinib and SYK inhibitors triggered synthetic killing of MYD88-mutated lymphoma cells. Our findings extend the spectrum of mutated MYD88 pro-survival signaling to include SYK directed BCR cross talk in MYD88-mutated lymphomas. Targeting SYK in combination with ibrutinib produces synthetic lethality, providing a framework for the clinical investigation of ibrutinib with SYK inhibitors in MYD88-mutated lymphomas.