Yang Liuqing, Lin Chunru, Liu Zhi-Ren
Department of Biology, Georgia State University, University Plaza, Atlanta, GA 30303, USA.
Cell Signal. 2005 Dec;17(12):1495-504. doi: 10.1016/j.cellsig.2005.03.008.
P68 nuclear RNA helicase is essential for normal cell growth. The protein plays a very important role in cell development and proliferation. However, the molecular mechanism by which the p68 functions in cell developmental program is not clear. We previously observed that bacterially expressed his-p68 was phosphorylated at multiple sites including serine/threonine and tyrosine [L. Yang, Z.R. Liu, Protein Expr. Purif., 35: 327]. Here we report that p68 RNA helicase is phosphorylated at tyrosine residue(s) in HeLa cells. Phosphorylation of p68 at threonine or tyrosine residues responds differently to tumor necrosis factor alpha (TNF-alpha)induced cell signal. Kinase inhibition and in vitro kinase assays demonstrate that p68 RNA helicase is a cellular target of p38 MAP kinase. Phosphorylation of p68 affects the ATPase and RNA unwinding activities of the protein. In addition, we demonstrate here that phosphorylation of p68 RNA helicase controls the function of the protein in the pre-mRNA splicing process. Interestingly, phosphorylation at different amino acid residues exhibits different regulatory effects. The data suggest that function(s) of p68 RNA helicase may be subjected to the regulation of multiple cell signal pathways.
P68核RNA解旋酶对正常细胞生长至关重要。该蛋白在细胞发育和增殖中发挥着非常重要的作用。然而，p68在细胞发育程序中发挥作用的分子机制尚不清楚。我们之前观察到，细菌表达的his-p68在包括丝氨酸/苏氨酸和酪氨酸在内的多个位点被磷酸化[L. Yang, Z.R. Liu, Protein Expr. Purif., 35: 327]。在此我们报告，p68 RNA解旋酶在HeLa细胞中的酪氨酸残基处被磷酸化。p68在苏氨酸或酪氨酸残基处的磷酸化对肿瘤坏死因子α（TNF-α）诱导的细胞信号有不同反应。激酶抑制和体外激酶分析表明，p68 RNA解旋酶是p38丝裂原活化蛋白激酶的细胞靶点。p68的磷酸化影响该蛋白的ATP酶和RNA解旋活性。此外，我们在此证明，p68 RNA解旋酶的磷酸化在mRNA前体剪接过程中控制该蛋白的功能。有趣的是，不同氨基酸残基处的磷酸化表现出不同的调节作用。这些数据表明，p68 RNA解旋酶的功能可能受到多种细胞信号通路的调节。
