PPP1R3 gene (Protein phosphatase 1) alterations in colorectal cancers

[目的]蛋白磷酸酶通过磷酸化和去磷酸化来控制细胞内的各种信息，如细胞内信号转导、细胞周期和代谢系统。其中，PPP1R3基因位于染色体7q31上，编码蛋白磷酸酶1(调节3)。最近有报道称，各种磷酸酶蛋白的失活会导致细胞分裂和细胞生长系统的异常。本研究分析了PPP1R3基因的突变情况。[方法]对我科收治的50例结直肠癌患者进行分析。从正常组织和结直肠癌原发灶中提取DNA，进行SSCP。对显示异常SSCP模式的DNA样本进行测序，以分析PPP1R3基因的突变。[结果](1)50例结直肠癌PPP1R3基因SSCP分析显示，6例(12%)PPP1R3基因异常。(2)对6例SSCP异常标本进行DNA测序，证实4例为外显子4点突变，2例为外显子1点突变。(3)PPP1R3全长基因增强了荧光素酶活性。然而，当检测含有外显子1或外显子4的点突变缺失突变体的荧光素酶活性时，外显子1缺失突变体的活性增强减弱，外显子4缺失突变体的活性没有增强。[结论]PPP1R3基因突变及其对细胞内转录活性的影响在结直肠癌中存在。这些发现表明，蛋白磷酸酶1(调节性3)蛋白参与了一些结直肠癌的细胞内过程。

[Objective] Protein phosphatases are known to control various intracellular information such as intracellular signal transduction, cell cycling, and metabolic systems, through phosphorylation and dephosphorylation. Among the genes encoding them, the PPP1R3 gene is located on chromosome 7q31, and encodes protein phosphatase 1 (regulatory 3). It has recently been reported that the inactivation of various phosphatase proteins causes abnormalities of cell division and cell growth systems. This study analyzed mutations in the PPP1R3 gene.[Methods] Fifty patients with colorectal cancer who had uhdergone resection in our department were analyzed. DNA was extracted from normal tissue and primary lesions of colorectal cancer, and subjected to SSCP. DNA samples showing abnormal SSCP patterns were sequenced to analyze mutations in the PPP1R3 gene. Deletion mutants of exons containing mutations were prepared and assayed for intranuclear transcription activity.[Results] (1) SSCP analysis of PPP1R3 showed abnormal patterns in 6 (12%) of the 50 colorectal cancers. (2) DNA sequencing of the 6 samples showing abnormal SSCP patterns confirmed point mutations in exon 4 in 4 samples, and in exon 1 in 2 samples. (3) Enhancement of luciferase activity by the full PPP1R3 gene was confirmed. However, when deletion mutants of point mutation-containing exon 1 or exon 4 were examined for luciferase activity, enhancement of the activity was decreased in the exon 1 deletion mutants, and no enhancement of the activity was noted in the exon 4 deletion mutants.[Conclusion] Mutations in the PPP1R3 gene and their effects on intracellular transcription activity were observed in colorectal cancers. These findings suggest that protein phosphatase 1 (regulatory 3) protein is involved in intracellular processes in some colorectal cancers.