β-TrCP-mediated ubiquitination and degradation of liver-enriched transcription factor CREB-H

CREB-H is an endoplasmic reticulum-resident bZIP transcription factor which critically regulates lipid homeostasis and gluconeogenesis in the liver. CREB-H is proteolytically activated by regulated intramembrane proteolysis to generate a C-terminally truncated form known as CREB-H-ΔTC, which translocates to the nucleus to activate target gene expression. CREB-H-ΔTC is a fast turnover protein but the mechanism governing its destruction was not well understood. In this study, we report on β-TrCP-dependent ubiquitination and proteasomal degradation of CREB-H-ΔTC. The degradation of CREB-H-ΔTC was mediated by lysine 48-linked polyubiquitination and could be inhibited by proteasome inhibitor. CREB-H-ΔTC physically interacted with β-TrCP, a substrate recognition subunit of the SCFβ-TrCP E3 ubiquitin ligase. Forced expression of β-TrCP increased the polyubiquitination and decreased the stability of CREB-H-ΔTC, whereas knockdown of β-TrCP had the opposite effect. An evolutionarily conserved sequence, SDSGIS, was identified in CREB-H-ΔTC, which functioned as the β-TrCP-binding motif. CREB-H-ΔTC lacking this motif was stabilized and resistant to β-TrCP-induced polyubiquitination. This motif was a phosphodegron and its phosphorylation was required for β-TrCP recognition. Furthermore, two inhibitory phosphorylation sites close to the phosphodegron were identified. Taken together, our work revealed a new intracellular signaling pathway that controls ubiquitination and degradation of the active form of CREB-H transcription factor.published_or_final_versio

Requirement of CRTC1 coactivator for hepatitis B virus transcription

Transcription of hepatitis B virus (HBV) from the covalently closed circular DNA (cccDNA) template is essential for its replication. Suppressing the level and transcriptional activity of cccDNA might have anti-HBV effect. Although cellular transcription factors, such as CREB, which mediate HBV transcription, have been well described, transcriptional coactivators that facilitate this process are incompletely understood. In this study we showed that CREB-regulated transcriptional coactivator 1 (CRTC1) is required for HBV transcription and replication. The steady-state levels of CRTC1 protein were elevated in HBV-positive hepatoma cells and liver tissues. Ectopic expression of CRTC1 or its homolog CRTC2 or CRTC3 in hepatoma cells stimulated the activity of the preS2/S promoter of HBV, whereas overexpression of a dominant inactive form of CRTC1 inhibited HBV transcription. CRTC1 interacts with CREB and they are mutually required for the recruitment to the preS2/S promoter on cccDNA and for the activation of HBV transcription. Accumulation of pregenomic RNA (pgRNA) and cccDNA was observed when CRTC1 or its homologs were overexpressed, whereas the levels of pgRNA, cccDNA and secreted HBsAg were diminished when CRTC1 was compromised. In addition, HBV transactivator protein HBx stabilized CRTC1 and promoted its activity on HBV transcription. Our work reveals an essential role of CRTC1 coactivator in facilitating and supporting HBV transcription and replication.published_or_final_versio

Interplay between SIRT1 and hepatitis B virus X protein in the activation of viral transcription

postprin

β-TrCP targets liver-enriched and membrane-bound transcription factor CREB-H for ubiquitination and degradation

Conference Theme: Signaling Pathways in Development, Diseases and Agin

Regulation of ubiquitination and degradation of CRTC1 transcriptional coactivator by salt-inducible kinase SIK1

Conference Theme: Signaling Pathways in Development, Diseases and Agin

Retroviral oncoprotein Tax-induced activation of LKB1-SIK and SIRT1 signaling in the regulation of HTLV-1 transcription

Session 7G - Oncogenic Viruses: no. 7G-6Conference Theme: Scientific Discovery for Human Healt

Suppression of HTLV-1 transcription by SIRT1 deacetylase

Conference Theme: HTLV and Related RetrovirusesPoster presentationInfection with HTLV-1 causes adult T-cell leukemia and tropical spastic paraparesis in different subsets of infected people. Treatments for HTLV-1-associated diseases are unspecific and unsatisfactory. Prophylactic measures have not been developed. Although HTLV-1 pathogenesis involves multiple stages and factors, high proviral load has been singled out as a major risk factor which predicts disease. HTLV-1 encodes Tax transactivator that potently activates transcription from viral long terminal repeats (LTR) and cellular promoters harbouring cAMP-responsive or KB element. Blocking Tax activity in infected cells should provide prophylactic and therapeutic benefits. In this study, we characterize the negative regulatory role of SIRT1 deacetylase in Tax-induced activation of HTLV-1 LTR. SIRT1 is a sirtuin with anti-cancer and anti-aging activity. Whereas over expression of SIRT1 abolished the activity of Tax to activate the LTR, compromising SIRT1 by RNA interference augmented Tax activation of the LTR. Resveratrol is a natural inhibitor of SIRT1 widely sold as a nutritional supplement and extensively tested for beneficial effects in various diseases. A SIRT1-dependent inhibition of the transcriptional activity of Tax was observed in cells treated with resveratrol. Consistently, treatment of HTLV-1-transformed T cells with resveratrol led to the activation of SIRT1 and the suppression of HTLV-1 proviral transcription. On the contrary, specific inhibition of SIRT1 by Sirtinol or Ex527 promoted HTLV-1 mRNA expression. The amount of HTLV-1 virion collected from culture supernatant was decreased in MT2 cells treated with resveratrol. Tax was found to interact with SIRT1 in HTLV-1-transformed T cells. Administration of resveratrol blocked the interaction of Tax with CREB and suppressed the recruitment of CREB and CRTC1 to the LTR. Taken together, our findings document the suppression of Tax activation of HTLV-1 transcription by SIRT1 and reveal potential benefits of small-molecule activators of SIRT1 such as resveratrol in the prevention and intervention of HTLV-1-associated diseases. Supported by SKY-MRF (2011), HK-RGC (HKU7674/12M, HKU7686/13M and HKU1/CRF/11G) and HK-HMRF (13121052) grants.link_to_OA_fulltex