Oh E S, Woods A, Couchman J R
Department of Cell Biology and the Cell Adhesion and Matrix Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
J Biol Chem. 1997 May 2;272(18):11805-11. doi: 10.1074/jbc.272.18.11805.
The transmembrane proteoglycan syndecan-4, which is a coreceptor with integrins in cytoskeleton-matrix interactions, appears to be multimerized in vivo. Both purified and recombinant core proteins form sodium dodecyl sulfate-resistant oligomers, and we now report that a synthetic peptide corresponding to the central region of syndecan-4 cytoplasmic domain (4V) also oligomerizes. The degree of oligomerization correlates with the previously reported ability to bind protein kinase C (PKC) and regulate its activity. Only multimeric recombinant syndecan-4 core protein, but not the monomeric protein, potentiated the activity of PKCalpha, and only oligomeric syndecan-4 cytoplasmic peptides were active. Changes in peptide sequence caused parallel loss of stable oligomeric status and ability to regulate a mixture of PKCalphabetagamma activity. A synthetic peptide encompassing the whole cytoplasmic domain of syndecan-4 (4L) containing a membrane-proximal basic sequence did not form higher order oligomers and could not regulate the activity of PKCalphabetagamma unless induced to aggregate by phosphatidylinositol 4,5-bisphosphate. Oligomerization and PKC regulatory activity of the 4V peptide were both increased by addition of N-terminal cysteine and reduced by phosphorylation of the cysteine thiol group. Concentration of syndecan-4 at sites of focal adhesion formation may enhance multimerization and both localize PKC and potentiate its activity to induce stable complex formation.
跨膜蛋白聚糖syndecan-4是细胞骨架与基质相互作用中整合素的共受体，在体内似乎会多聚化。纯化的和重组的核心蛋白均能形成抗十二烷基硫酸钠的寡聚体，我们现在报告，与syndecan-4细胞质结构域（4V）中央区域对应的合成肽也会寡聚化。寡聚化程度与先前报道的结合蛋白激酶C（PKC）并调节其活性的能力相关。只有多聚体的重组syndecan-4核心蛋白，而不是单体蛋白，能增强PKCα的活性，并且只有寡聚的syndecan-4细胞质肽具有活性。肽序列的改变导致稳定寡聚状态和调节PKCαβγ活性混合物能力的平行丧失。包含syndecan-4整个细胞质结构域（4L）且含有膜近端碱性序列的合成肽不会形成高阶寡聚体，并且除非被磷脂酰肌醇4,5-二磷酸诱导聚集，否则无法调节PKCαβγ的活性。4V肽的寡聚化和PKC调节活性都因添加N端半胱氨酸而增加，因半胱氨酸硫醇基团的磷酸化而降低。syndecan-4在粘着斑形成位点的浓度可能会增强多聚化，并使PKC定位并增强其活性以诱导稳定复合物的形成。
