Introduction and objectiveCholesterol homeostasis is a culmination of cellular synthesis, efflux, and catabolism to important physiological entities where short chain fatty acid, butyrate embodied as a key player. This discourse probes the mechanistic molecular details of butyrate action in maintaining host-cholesterol balance.MethodsHepatic mir-122 being the most indispensable regulator of cholesterol metabolic enzymes, we studied upstream players of mir-122 biogenesis in the presence and absence of butyrate in Huh7 cells and mice model. We synthesized unique self-transfecting GMO (guanidinium-morpholino-oligo) linked PMO (Phosphorodiamidate-Morpholino Oligo)-based antisense cell-penetrating reagent to selectively knock down the key player in butyrate mediated cholesterol regulation.ResultsWe showed that butyrate treatment caused upregulation of RNA-binding protein, AUF1 resulting in RNase-III nuclease, Dicer1 instability, and significant diminution of mir-122. We proved the importance of AUF1 and sequential downstream players in AUF1-knock-down mice. Injection of GMO-PMO of AUF1 in mouse caused near absence of AUF1 coupled with increased Dicer1 and mir-122, and reduced serum cholesterol regardless of butyrate treatment indicating that butyrate acts through AUF1.ConclusionThe roster of intracellular players was as follows: AUF1-Dicer1-mir-122 for triggering butyrate driven hypocholesterolemia. To our knowledge this is the first report linking AUF-1 with cholesterol biogenesis.

STING-Type I interferon (IFN) signaling in myeloid cells plays a critical role in effective antitumor immune responses, but STING agonist as monotherapy has shown limited efficacy in clinical trials. The mechanisms that downregulate STING signaling are not fully understood. Here, we report that Protein phosphatase 2A (PP2A) with its specific B regulatory subunit STRN4 negatively regulated STING-Type I IFN in macrophages. Mice with macrophages PP2A deficiency exhibited reduced tumor progression.The tumor microenvironment showed decreased immunosuppressive and increased IFN-activated macrophages and CD8+ T cells. Mechanistically, we demonstrated that hippo kinase MST1/2 was required for STING activation. STING agonist induced dissociation of PP2A from MST1/2 in normal macrophages, but not in tumor conditioned macrophages. Furthermore, our data showed that STRN4 mediated PP2A binding to and dephosphorylation of hippo kinase MST1/2, resulting in stabilization of YAP/TAZ to antagonize STING activation. In human GBM patients, YAP/TAZ was highly expressed in tumor-associated macrophages but not in non-tumor macrophages. We also demonstrated that PP2A/STRN4 deficiency in macrophages reduced YAP/TAZ expression and sensitized tumor conditioned macrophages to STING stimulation. In summary, we demonstrated that PP2A/STRN4-YAP/TAZ is a previously unappreciated mechanism that mediate immunosuppression in tumorassociated macrophages and targeting PP2A/STRN4-YAP/TAZ axis can sensitize tumors to immunotherapy.

This discourse probes the mechanistic molecular details of butyrate action in maintaining host- cholesterol balance. Hepatic miR122 being the most indispensable regulator of cholesterol metabolic enzymes, we studied upstream players of miR122 biogenesis in the presence and absence of butyrate in Huh7 cells and mice model. We showed that butyrate treatment caused upregulation of RNA-binding protein, AUF-1 resulting in RNase-III nuclease, Dicer-1 instability, and significant diminution of miR122. We proved its importance of AUF-1 and sequential downstream players in AUF-1-knock-down mice. We synthesized unique self-transfecting GMO (guanidinium-morpholino- oligonucleotides) linked PMO (Phosphorodiamidate-Morpholino Oligonucleotides)-based antisense reagent and injection of which in mouse caused near absence of AUF-1 coupled with increased Dicer- 1 and miR122, and reduced serum cholesterol regardless of butyrate treatment indicating that butyrate acts though AUF-1. The roster of intracellular players was as follows: AUF-1-Dicer-1-miR122 for triggering butyrate driven hypocholesterlaemia. To our knowledge this is the first report linking AUF-1 with cholesterol biogenesis.

Glioblastoma (GBM) is an immunologically “cold” tumor that does not respond to current immunotherapy. Here, we demonstrate a fundamental role for the α-isoform of the catalytic subunit of protein phosphatase-2A (PP2Ac) in regulating glioma immunogenicity. Genetic ablation of PP2Ac in glioma cells enhanced double stranded DNA (dsDNA) production and cGAS-type I interferon (IFN) signaling, MHC-I expression, and tumor mutational burden. In co-culture experiments, PP2Ac deficiency in glioma cells promoted dendritic cell (DC) cross presentation and clonal expansion of CD8+ T cells. In vivo, PP2Ac depletion sensitized tumors to immune checkpoint blockade and radiotherapy treatment. Single cell analysis demonstrated that PP2Ac deficiency increased CD8+ T cell, NK cell, and DC accumulation and reduced immunosuppressive tumor associated macrophages. Furthermore, loss of PP2Ac increased IFN signaling in myeloid and tumor cells and reduced expression of a tumor gene signature associated with worse patient survival in TCGA. Collectively, this study establishes a novel role for PP2Ac in inhibiting dsDNA-cGAS-STING signaling to suppress anti-tumor immunity in glioma.