Analysis of splicing variant of p53-inducible phosphatase PPM1D on carcinogenesis

PPM1D是一种PPM1型蛋白磷酸酶，在DNA损伤时被诱导。在我们目前的研究中，我们在mRNA和蛋白水平上鉴定并表征了人类PPM1D的另一种剪接变体（标记为PPM1D430）。PPM1D430包含已知PPM1D蛋白（PPM1D605）的420个常见残基，并包含一段PPM1D430特异性的10个氨基酸。半定量RT-PCR分析显示，PPM1D430 mRNA也以p53依赖的方式被诱导响应基因毒性胁迫。体外磷酸酶分析和PPM1D430特异性RNA干扰分析进一步表明，PPM1D430在体外和体内均能使人p53的Ser15去磷酸化。另一方面，通过对人体组织cDNA面板的RT-PCR分析，该基因的表达谱显示PPM1D430仅在睾丸和白细胞中表达，而PPM1D605则普遍存在。此外，在某些条件下，PPM1D430与PPM1D605表现出不同的亚细胞定位模式和蛋白质稳定性。因此，我们目前的研究结果表明PPM1D430可能在免疫反应和/或精子发生中发挥特定功能。

PPM1D is a PPM1 type protein phosphatase and is induced in response to DNA damage. In our current study, we identify and characterize an alternative splicing variant (denoted PPM1D430) of human PPM1D at both the mRNA and protein level. PPM1D430 comprises the common 420 residues of the known PPM1D protein (PPM1D605) and contains a stretch of PPM1D430-specific 10 amino acids. Semi-quantitative RT-PCR analysis revealed that PPM1D430 mRNA is also induced in response to the genotoxic stress in a p53-dependent manner. In vitro phosphatase analysis and PPM1D430-specific RNA interference analysis further indicated that PPM1D430 can dephosphorylate Ser15 of human p53 both in vitro and in vivo. On the other hand, expression profiling of this gene by RT-PCR analysis of a human tissue cDNA panel revealed that PPM1D430 is expressed exclusively in testes and in leukocytes whereas PPM1D605 is ubiquitous. In addition, PPM1D430 shows a different subcellular localization pattern and protein stability when compared with PPM1D605 under some conditions. Our current findings thus suggest that PPM1D430 may exert specific functions in immune response and/or spermatogenesis.