Research for a protein tyrosine phosphatase for cell adhesion and its mutations in gastrointestinal cancers.

由于酪氨酸磷酸化水平是由蛋白酪氨酸激酶和蛋白酪氨酸磷酸酶（PTPases）的作用平衡决定的，因此除了PTKs的不调节激活外，PTPases的失活也可能参与了胃肠道细胞的恶性转化。PTPH1是一种人类非跨膜型PTPase，最近已被分子克隆。这种酶含有一个类似ezrin的结构，在它的n端区域有一个PDZ结构域。由于ezrin样结构被认为参与细胞粘附，PTPH1可能位于细胞粘附位点，并通过控制细胞粘附位点蛋白的酪氨酸磷酸化来调节细胞粘附。在这项研究中，我们探讨了PTPH1的生理作用和PTPH1的临床应用。(1) PTPH1位于细胞粘附位点。(2)将PTPH1突变体转染到培养的细胞中，在细胞粘附方面没有任何变化。我们将进一步研究在培养细胞中微量注射PTPH1抗体的效果。(3)利用RT-P CR检测了PTPH1基因在多种胃肠道肿瘤中的突变情况。我们在胃肠道肿瘤样本中发现了PTPH1基因的几个突变。我们将进一步研究在胃肠道癌症中发现的突变是否会导致这些癌症的发生。此外，我们将尝试通过酵母双杂交系统鉴定与PTPH1的Ezrin结构域或PDZ结构域结合的蛋白。

Since the level of tyrosine phosphorylation is determined by the balance between the actions of both protein tyrosine kinases and protein tyrosine phosphatases (PTPases), not only the unregulated activation of PTKs but also the inactivation of PTPases may be involved in the malignant transformation of gastrointestinal cells. PTPH1 is a human non-transmembrane-type PTPase that has recently been molecularly cloned. This enzyme contains an Ezrin-like structure and a PDZ domain in its N-terminal region. Since Ezrin-like structures are suggested to be involved in cell adhesion, PTPH1 may locate at the cell adhesion sites and regulate cell adhesion through the control of tyrosine phosphorylation of proteins at cell adhesion sites. In this study, we investigated the physiological roles of PTPH1 and clinical applications of PTPH1. (1) PTPH1 located at cell adhesion sites. (2) Transfection of PTPH1 mutants into cultured cells did not show any changes in terms of cell adhesion. We will further examine the effect of microinjection of antibody to PTPH1 into cultured cells. (3) With the use of RT-P CR, we have examined the mutations of PTPH1 gene in various gastrointestinal cancers. We have found several mutations in PTPH1 gene in gastrointestinal cancer sample. We will further investigate whether the mutations found in gastrointestinal cancers results in oncogenesis of these cancers. In addition, we will try to identify the proteins bound to the Ezrin domain or the PDZ domain of PTPH1 by the yeast two-hybrid system.