核受体辅活化子PNRC与孤儿核受体SF1的相互作用有赖于SF1的AF-2功能结构域

核受体辅活化子PNRC(proline richnuclearreceptorcoregulatoryprotein ,富含脯氨酸的核受体辅调节蛋白 )可通过含SH3结合模体的PNRC2 78 30 0区域与孤儿核受体类固醇生成因子 1(steroido genicfactor 1,SF1)相互作用 .激活功能 2 (activationfunction 2 ,AF 2 )结构域在核受体配体依赖性转录激活中发挥了重要作用 ,为探讨AF 2结构域在SF1转录激活中的作用机制 ,采用酵母双杂合分析、缺失突变技术和瞬时转染等研究方法考察了AF 2结构域对SF1反式激活功能及SF1与PNRC相互作用的影响 .SF1的反式激活功能有赖于AF 2结构域 ,其机制是SF1AF 2结构域的突变严重影响了SF1与PNRC的有效相互作用 ,并消除了PNRC对SF1反式激活功能的辅激活作用 .结果表明 ,SF1与PNRC的相互作用有赖于AF 2的功能结构域     

NRIP, a novel calmodulin binding protein, activates calcineurin to dephosphorylate human papillomavirus E2 protein

Previously, we found a gene named nuclear receptor interaction protein (NRIP) (or DCAF6 or IQWD1). We demonstrate that NRIP is a novel binding protein for human papillomavirus 16 (HPV-16) E2 protein. HPV-16 E2 and NRIP can directly associate into a complex in vivo and in vitro, and the N-terminal domain of NRIP interacts with the transactivation domain of HPV-16 E2. Only full-length NRIP can stabilize E2 protein and induce HPV gene expression, and NRIP silenced by two designed small interfering RNAs (siRNAs) decreases E2 protein levels and E2-driven gene expression. We found that NRIP can directly bind with calmodulin in the presence of calcium through its IQ domain, resulting in decreased E2 ubiquitination and increased E2 protein stability. Complex formation between NRIP and calcium/calmodulin activates the phosphatase calcineurin to dephosphorylate E2 and increase E2 protein stability. We present evidences for E2 phosphorylation in vivo and show that NRIP acts as a scaffold to recruit E2 and calcium/calmodulin to prevent polyubiquitination and degradation of E2, enhancing E2 stability and E2-driven gene expression.     

Hepatitis B virus X protein modulates peroxisome proliferator-activated receptor gamma through protein-protein interaction

Ligand activation of peroxisome proliferator-activated receptor gamma (PPARgamma) has been reported to induce growth inhibition and apoptosis in various cancers including hepatocellular carcinoma (HCC). However, the effect of hepatitis B virus X protein (HBx) on PPARgamma activation has not been characterized in hepatitis B virus (HBV)-associated HCC. Herein, we demonstrated that HBx counteracted growth inhibition caused by PPARgamma ligand in HBx-associated HCC cells. We found that HBx bound to DNA binding domain of PPARgamma and HBx/PPARgamma interaction blocked nuclear localization and binding to recognition site of PPARgamma. HBx significantly suppressed a PPARgamma-mediated transactivation. These results suggest that HBx modulates PPARgamma function through protein-protein interaction.