Department of Microbiology and Molecular Cell Biology, The Leroy T. Canoles Jr Cancer Research Center, Eastern Virginia Medical School, Norfolk, VA 23508, USA.
Blood. 2012 Feb 2;119(5):1173-81. doi: 10.1182/blood-2011-06-358564. Epub 2011 Nov 21.
The Really Interesting New Gene (RING) Finger Protein 4 (RNF4) represents a class of ubiquitin ligases that target Small Ubiquitin-like Modifier (SUMO)-modified proteins for ubiquitin modification. To date, the regulatory function of RNF4 appears to be ubiquitin-mediated degradation of sumoylated cellular proteins. In the present study, we show that the Human T-cell Leukemia Virus Type 1 (HTLV-1) oncoprotein Tax is a substrate for RNF4 both in vivo and in vitro. We mapped the RNF4-binding site to a region adjacent to the Tax ubiquitin/SUMO modification sites K280/K284. Interestingly, RNF4 modification of Tax protein results in relocalization of the oncoprotein from the nucleus to the cytoplasm. Overexpression of RNF4, but not the RNF4 RING mutant, resulted in cytoplasmic enrichment of Tax. The RNF4-induced nucleus-to-cytoplasm relocalization was associated with increased NF-κB-mediated and decreased cAMP Response Element-Binding (CREB)-mediated Tax activity. Finally, depletion of RNF4 by RNAi prevented the DNA damage-induced nuclear/cytoplasmic translocation of Tax. These results provide important new insight into STUbL-mediated pathways that regulate the subcellular localization and functional dynamics of viral oncogenes.
真核延伸因子 4（RNF4）是一种新型的环指蛋白，属于泛素连接酶家族，可识别并结合 SUMO 化修饰的蛋白，进而对其进行泛素化修饰。目前研究表明，RNF4 的调控功能主要是通过泛素化介导 SUMO 化修饰蛋白的降解。在本研究中，我们发现人类 T 细胞白血病病毒 1 型（HTLV-1）癌蛋白 Tax 是 RNF4 的体内和体外底物。我们将 RNF4 的结合位点定位于 Tax 的泛素/SUMO 修饰位点 K280/K284 附近的一个区域。有趣的是，RNF4 对 Tax 蛋白的修饰导致该致癌蛋白从细胞核重新定位到细胞质。RNF4 的过表达，但不是 RNF4 RING 突变体，导致 Tax 在细胞质中的积累。RNF4 诱导的核质重新定位与 NF-κB 介导的活性增加和 cAMP 反应元件结合（CREB）介导的 Tax 活性降低有关。最后，RNAi 敲低 RNF4 可防止 DNA 损伤诱导的 Tax 从核内到细胞质的易位。这些结果为 STUbL 介导的途径提供了重要的新见解，这些途径调节病毒癌基因的亚细胞定位和功能动态。
