Critical and distinct roles of amino- and carboxyl-terminal sequences in regulation of the biological activity of the Chp atypical Rho GTPase
Critical and distinct roles of amino- and carboxyl-terminal sequences in regulation of the biological activity of the Chp atypical Rho GTPase
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DOI：
10.1074/jbc.m411300200
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发表时间：
2005-04-08
影响因子：
4.8
通讯作者：
Der, CJ
中科院分区：
文献类型：
--
作者：
Chenette, EJ;Abo, A;Der, CJ
Chp（Cdc 42同源蛋白）与人Cdc 42小GTP酶具有显著的序列和功能同一性，并且像Cdc 42一样，促进丝状伪足的形成并激活p21激活的激酶丝氨酸/苏氨酸激酶。然而，与Cdc 42不同，Chp含有独特的氨基和羧基末端延伸。在这里，我们确定是否Chp，像Cdc 42，可以促进生长转化和评估的作用，Chp功能的氨基和羧基末端序列。令人惊讶的是，我们发现，GTP酶缺陷突变体的Chp表现出低的转化活性，但删除的氨基末端的Chp大大提高其转化活性。因此，氨基末端可以作为Chp功能的负调节剂。Cdc 42的羧基末端含有CAAX（其中C是半胱氨酸，A是脂肪族氨基酸，X是末端氨基酸）四肽序列，其发出对Cdc 42膜缔合和生物学功能至关重要的翻译后修饰的信号。虽然Chp缺乏aCAAX基序，但我们发现Chp显示羧基末端依赖性定位于质膜和内体。此外，一个完整的羧基末端所需的Chp转化活性。然而，蛋白质棕榈酰化，但不异戊二烯化的抑制剂治疗，导致Chp错误定位到细胞质。因此，Chp依赖于棕榈酰化，而不是异戊二烯化，用于膜缔合和功能。总之，Chp与细胞转化有关，Chp独特的氨基和羧基末端代表了Rho GT3功能调节的非典型机制。
Chp (Cdc42 homologous protein) shares significant sequence and functional identity with the human Cdc42 small GTPase, and like Cdc42, promotes formation of filopodia and activates the p21-activated kinase serine/threonine kinase. However, unlike Cdc42, Chp contains unique amino- and carboxyl-terminal extensions. Here we determined whether Chp, like Cdc42, can promote growth transformation and evaluated the role of the amino- and carboxyl-terminal sequences in Chp function. Surprisingly, we found that a GTPase-deficient mutant of Chp exhibited low transforming activity but that deletion of the amino terminus of Chp greatly enhanced its transforming activity. Thus, the amino terminus may serve as a negative regulator of Chp function. The carboxyl terminus of Cdc42 contains a CAAX ( where C is cysteine, A is aliphatic amino acid, X is terminal amino acid) tetrapeptide sequence that signals for the post-translational modification critical for Cdc42 membrane association and biological function. Although Chp lacks aCAAXmotif, we found that Chp showed carboxylterminus-dependent localization to the plasma membrane and to endosomes. Furthermore, an intact carboxyl terminus was required for Chp transforming activity. However, treatment with inhibitors of protein palmitoylation, but not prenylation, caused Chp to mislocalize to the cytoplasm. Thus, Chp depends on palmitoylation, rather than isoprenylation, for membrane association and function. In summary, Chp is implicated in cell transformation, and the unique amino and carboxyl termini of Chp represent atypical mechanisms of regulation of Rho GTPase function.