CNSC-26. INVESTIGATING THE ROLE OF QUAKING IN REGULATING MHC II ANTIGEN PRESENTATION IN TUMOR-ASSOCIATED MACROPHAGES OF GBM

Abstract Glioblastoma (GBM) is the most common and malignant primary brain tumor with a median survival rate of 14 months. Despite the success of immunotherapy in treating various cancer types, its efficacy remains poor in GBM. Such limitation can be attributed to the profound immunosuppressive tumor microenvironment of GBM enriched with the tumor-associated macrophages (TAMs). Quaking (Qki) is an RNA-binding protein that is mutated or deleted in more than 35% of GBM patients. Decreased levels of Qki in TAMs associates with worsened survival rates and responsiveness to immunotherapy in GBM mouse and patients. Moreover, Qki is a tumor suppressor gene in GBM and a major regulator in phagocytosis, a fundamental biological process in delivering antigens to major histocompatibility complex class II (MHC II). MHC II-restricted antigen presentation in macrophages of GBM is important in maintaining the fitness of cytotoxic and helper T cells required in anti-tumor response. However, the mechanism through which Qki regulates MHCII expression and presentation has yet to be elucidated. I hypothesize that Qki promotes MHC II expression in TAMs, thereby constraining the development and progression of GBM. In vitro assays like immunofluorescent staining, qRT-PCR, cell co-culture system, and flow cytometry will be performed involving QPP (Qk-/-Trp53-/-; Pten-/-) mouse brains, QPP cells, and mouse macrophage cell lines. A positive correlation between transcriptomic and protein expression levels of Qki, MHC II, and CIITA (a master regulator of MHC II) was confirmed in both mouse QPP and human GBM samples. Moreover, bone-marrow-derived macrophages activated by QPP cell supernatant shows upregulated levels of Qki and thus MHC II genes. A preliminary conclusion is that Qki plays a permissive role in MHCII expression in TAMs of GBM. Further downstream impact of Qki in TAMs will be evaluated in T cell activity and in transcription of MHC II in TAMs.