Identification of interacting proteins of retinoid-related orphan nuclear receptor gamma in HepG2 cells

The ribosomal S6 kinase inhibitor BI-D1870 ameliorated experimental autoimmune encephalomyelitis in mice

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system (CNS) caused by the infiltration of TH1 and TH17 cells into the CNS. Ribosomal S6 kinase 2 (RSK2; RPS6KA3) regulates TH17 differentiation by attenuating RORγt transcriptional activities and IL-17A production. The pan-RSK inhibitor BI-D1870 also inhibits TH17 differentiation, but the effect of BI-D1870 in vivo remains unclear. Here, we generated mice with experimental autoimmune encephalomyelitis (EAE) and treated them with BI-D1870. BI-D1870 administration protected mice from EAE by reducing the infiltration of TH1 and TH17 cells into the CNS and decreasing mRNA levels of Ccr6 in TH17 cells. These results suggest that RSK inhibition is a promising strategy for the treatment of MS.

The GABAB receptor associates with regulators of G-protein signaling 4 protein in the mouse prefrontal cortex and hypothalamus

Regulators of G-protein signaling (RGS) proteins regulate certain G-protein-coupled receptor (GPCR)-mediated signaling pathways. The GABA_B receptor (GABA_BR) is a GPCR that plays a role in the stress response. Previous studies indicate that acute immobilization stress (AIS) decreases RGS4 in the prefrontal cortex (PFC) and hypothalamus (HY) and suggest the possibility of a signal complex composed of RGS4 and GABA_BR. Therefore, in the present study, we tested whether RGS4 associates with GABA_BR in these brain regions. We found the co-localization of RGS4 and GABA_BR subtypes in the PFC and HY using double immunohistochemistry and confirmed a direct association between GABA_B2R and RGS4 proteins using co-immunoprecipitation. Furthermore, we found that AIS decreased the amount of RGS4 bound to GABA_B2R and the number of double-positive cells. These results indicate that GABA_BR forms a signal complex with RGS4 and suggests that RGS4 is a regulator of GABA_BR. [BMB Reports 2014; 47(6): 324-329]

DGCR14 induces Il17a gene expression through the RORγ/BAZ1B/RSKS2 complex

The Dgcr14/Es2 gene is located in a chromosomal region the loss of which has been associated with DiGeorge syndrome, a cause of immunodeficiency, heart defects, and skeletal abnormalities. However, the role of DGCR14 protein remains to be elucidated. Here, I found that DGCR14 protein acts as a coactivator of RORγt in TH17 cells. Biochemical purification of the RORγ coregulator complex allowed me to identify the associated DGCR14 protein by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Overexpression of Dgcr14 mRNA enhanced RORγt-mediated transcriptional activity and facilitated TH17 cell differentiation. Furthermore, knockdown of Dgcr14 reduced Il17a mRNA expression. I also found that DGCR14 associated with ribosomal S6 kinase 2 (RSK2, also called RpS6ka3) and BAZ1B, both of which were recruited to the Il17a promoter during TH17 cell differentiation. Knockdown of Baz1b or RpS6ka3 also reduced Il17a mRNA expression, and Baz1b knockdown increased transcriptional suppressive histone marks (histone H3K9me3) on the Il17a promoter. My findings showed the roles of DGCR14, RSK2, and BAZ1B in the transcriptional regulation of Il17a mRNA during TH17 cell differentiation.

CREB and FoxO1: two transcription factors for the regulation of hepatic gluconeogenesis

Liver plays a major role in maintaining glucose homeostasis in mammals. Under fasting conditions, hepatic glucose production is critical as a source of fuel to maintain the basic functions in other tissues, including skeletal muscle, red blood cells, and the brain. Fasting hormones glucagon and cortisol play major roles during the process, in part by activating the transcription of key enzyme genes in the gluconeogenesis such as phosphoenol pyruvate carboxykinase (PEPCK) and glucose 6 phosphatase catalytic subunit (G6Pase). Conversely, gluconeogenic transcription is repressed by pancreatic insulin under feeding conditions, which effectively inhibits transcriptional activator complexes by either promoting post-translational modifications or activating transcriptional inhibitors in the liver, resulting in the reduction of hepatic glucose output. The transcriptional regulatory machineries have been highlighted as targets for type 2 diabetes drugs to control glycemia, so understanding of the complex regulatory mechanisms for transcription circuits for hepatic gluconeogenesis is critical in the potential development of therapeutic tools for the treatment of this disease. In this review, the current understanding regarding the roles of two key transcriptional activators, CREB and FoxO1, in the regulation of hepatic gluconeogenic program is discussed.

Synergistic induction of TRAIL-mediated apoptosis by anisomycin in human hepatoma cells via the BH3-only protein Bid and c-Jun/AP-1 signaling pathway

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF super-family, and it has been shown that many human cancer cell lines are refractory to TRAIL-induced cell death. However, the molecular mechanisms underlying resistance are unclear. In the present study, we show that TRAIL-resistance is reversed in human hepatoma cells by anisomycin, which is known to inhibit protein synthesis and induce ribotoxic stress. Synergistic induction of apoptosis in cells treated with anisomycin plus TRAIL was associated with activation of caspases and cleavage of Bid, a pro-apoptotic BH3-only protein. Silencing of Bid expression by small interfering RNA (siRNA) significantly attenuated the loss of mitochondrial membrane potential (MMP, Δψm) and significantly increased induction of apoptosis in cells treated with anisomycin and TRAIL, confirming that Bid cleavage is required for the response. In addition, c-Jun/AP-1 was rapidly activated upon stimulation with anisomycin; however, the knockdown of c-Jun/AP-1 expression by c-Jun siRNA markedly reduced anisomycin plus TRAIL-induced loss of MMP and apoptosis. Taken together, the findings show that anisomycin sensitizes TRAIL-mediated hepatoma cell apoptosis via the mitochondria-associated pathway, involving the cleavage of Bid and activation of the c-Jun/AP-1 pathway, indicating that this compound can be used as an anti-tumor agent in combination with TRAIL.