The Phosphatase-Resistant Isoform of CaMKI, Ca2+/Calmodulin-Dependent Protein Kinase I未 (CaMKI未), Remains in Its 鈥淧rimed鈥?Form without Ca2+ Stimulation

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• 作者：Yukako Senga ; Atsuhiko Ishida ; Yasushi Shigeri ; Isamu Kameshita ; Noriyuki Sueyoshi
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：June 16, 2015
• 年：2015
• 卷：54
• 期：23
• 页码：3617-3630
• 全文大小：898K
• ISSN：1520-4995

文摘

Ca²⁺/calmodulin-dependent protein kinase I (CaMKI) is known to play pivotal roles in Ca²⁺ signaling pathways. Four isoforms of CaMKI (伪, 尾, 纬, and 未) have been reported so far. CaMKI is activated through phosphorylation by the upstream kinase, CaMK kinase (CaMKK), and phosphorylates downstream targets. When CaMKI was transiently expressed in 293T cells, CaMKI伪 was not phosphorylated at all under low-Ca²⁺ conditions in the cells. In contrast, we found that CaMKI未 was significantly phosphorylated and activated to phosphorylate cAMP response element-binding protein (CREB) under the same conditions. Herein, we report that the sustained activation of CaMKI未 is ascribed to its phosphatase resistance resulting from the structure of its N-terminal region. First, we examined whether CaMKI未 is more readily phosphorylated by CaMKK than CaMKI伪, but no significant difference was observed. Next, to compare the phosphatase resistance between CaMKI伪 and CaMKI未, we assessed the dephosphorylation of the phosphorylated CaMKIs by CaMK phosphatase (CaMKP/PPM1F). Surprisingly, CaMKI未 was hardly dephosphorylated by CaMKP, whereas CaMKI伪 was significantly dephosphorylated under the same conditions. To date, there have been no detailed reports concerning dephosphorylation of CaMKI. Through extensive analysis of CaMKP-catalyzed dephosphorylation of various chimeric and point mutants of CaMKI未 and CaMKI伪, we identified the amino acid residues responsible for the phosphatase resistance of CaMKI未 (Pro-57, Lys-62, Ser-66, Ile-68, and Arg-76). These results also indicate that the phosphatase resistance of CaMKI is largely affected by only several amino acids in its N-terminal region. The phosphatase-resistant CaMKI isoform may play a physiological role under low-Ca²⁺ conditions in the cells.