de la Vega Laureano, Fröbius Katrin, Moreno Rita, Calzado Marco A, Geng Hui, Schmitz M Lienhard
Institute of Biochemistry, Medical Faculty, Friedrichstrasse 24, Justus-Liebig-University, 35392 Giessen, Germany.
Biochim Biophys Acta. 2011 Feb;1813(2):283-97. doi: 10.1016/j.bbamcr.2010.11.022. Epub 2010 Dec 8.
The serine/threonine kinase HIPK2 regulates gene expression programs controlling differentiation and cell death. HIPK2 localizes in subnuclear speckles, but the structural components allowing this localization are not understood. A point mutation analysis allowed mapping two nuclear localization signals and a SUMO interaction motif (SIM) that also occurs in HIPK1 and HIPK3. The SIM binds all three major isoforms of SUMO (SUMO-1-3), while only SUMO-1 is capable of covalent conjugation to HIPK2. Deletion or mutation of the SIM prevented SUMO binding and precluded localization of HIPK2 in nuclear speckles, thus causing localization of HIPK2 to the entire cell. Functional inactivation of the SIM prohibited recruitment of HIPK2 to PML nuclear bodies and disrupted colocalization with other proteins such as the polycomb protein Pc2 in nuclear speckles. Interaction of HIPK2 with Pc2 or PML in intact cells was largely dependent on a functional SIM in HIPK2, highlighting the relevance of SUMO/SIM interactions as a molecular glue that serves to enhance protein/protein interaction networks. HIPK2 mutants with an inactive SIM showed changed activities, thus revealing that non-covalent binding of SUMO to the kinase is important for the regulation of its function.
丝氨酸/苏氨酸激酶HIPK2调控着控制分化和细胞死亡的基因表达程序。HIPK2定位于核内斑点，但促使这种定位的结构成分尚不清楚。通过点突变分析确定了两个核定位信号和一个SUMO相互作用基序（SIM），该基序也存在于HIPK1和HIPK3中。该SIM可结合SUMO的所有三种主要异构体（SUMO-1至3），而只有SUMO-1能够与HIPK2发生共价结合。SIM的缺失或突变会阻止SUMO结合，并使HIPK2无法定位于核斑点，从而导致HIPK2在整个细胞中定位。SIM的功能失活会阻止HIPK2募集到PML核体，并破坏其与其他蛋白质（如核斑点中的多梳蛋白Pc2）的共定位。在完整细胞中，HIPK2与Pc2或PML的相互作用很大程度上依赖于HIPK2中功能性的SIM，这突出了SUMO/SIM相互作用作为一种分子胶水增强蛋白质/蛋白质相互作用网络的重要性。具有失活SIM的HIPK2突变体表现出活性改变，这表明SUMO与该激酶的非共价结合对其功能调控很重要。
