Mamajiwalla S N, Burgess D R
Department of Biological Sciences, University of Pittsburgh, Pennsylvania 15260, USA.
Oncogene. 1995 Jul 20;11(2):377-86.
The family of mitogen activated protein (MAP) kinases appear to play a central role in relaying signals generated by receptor protein tyrosine kinases (RPTK) from the cell surface to the nucleus. We previously demonstrated that undifferentiated and mitotically active crypt cells have high levels of tyrosine phosphorylated proteins (DR Burgess, W Jiang, S Mamajiwalla and W Kinsey. 1989. J. Cell Biol., 109: 2139) possibly due to the activation of RPTKs and also have high pp60c-src protein tyrosine kinase activity (CA Cartwright, SN Mamajiwalla, SA Skolnik, W Eckhart and DR Burgess. 1993. Oncogene. 8: 1033) when compared to differentiated, non-mitotic villus cells. Since activation of RPTKs leading to cell proliferation or differentiation involves activation of the Ras-MAP kinase pathway, we chose to determine in this study if the activity of the MAP kinases were also regulated during differentiation of normal adult enterocytes. Our data show that although the 42 kD MAP kinase (p42mapk) was expressed in both crypt and villus cells, it was phosphorylated on tyrosine and active only in the crypt cells. Our data further suggest that p42mapk is inactivated during differentiation, possibly by a protein tyrosine phosphatase. Immunofluorescence studies revealed that p42mapk localized to the nuclei in both undifferentiated and differentiated enterocytes and colocalized with phosphotyrosine containing proteins at the region of the junctional complex. These results suggest that p42mapk and its regulators are tightly controlled during enterocyte differentiation in vivo and implicate p42mapk as a key regulatory molecule in the normal development of the adult intestinal epithelium.
丝裂原活化蛋白（MAP）激酶家族似乎在将受体蛋白酪氨酸激酶（RPTK）产生的信号从细胞表面传递到细胞核的过程中发挥核心作用。我们之前证明，未分化且有丝分裂活性的隐窝细胞中酪氨酸磷酸化蛋白水平较高（DR·伯吉斯、W·江、S·马马吉瓦拉和W·金西。1989年。《细胞生物学杂志》，109：2139），这可能是由于RPTK的激活，而且与分化的、非有丝分裂的绒毛细胞相比，其pp60c-src蛋白酪氨酸激酶活性也较高（CA·卡特赖特、SN·马马吉瓦拉、SA·斯科尔尼克、W·埃克哈特和DR·伯吉斯。1993年。《癌基因》。8：1033）。由于RPTK的激活导致细胞增殖或分化涉及Ras-MAP激酶途径的激活，我们在本研究中选择确定MAP激酶的活性在正常成年肠上皮细胞分化过程中是否也受到调节。我们的数据表明，尽管42 kD MAP激酶（p42mapk）在隐窝细胞和绒毛细胞中均有表达，但它仅在隐窝细胞中发生酪氨酸磷酸化并具有活性。我们的数据进一步表明，p42mapk在分化过程中失活，可能是通过一种蛋白酪氨酸磷酸酶。免疫荧光研究显示，p42mapk在未分化和分化的肠上皮细胞中均定位于细胞核，并在连接复合体区域与含磷酸酪氨酸的蛋白共定位。这些结果表明，在体内肠上皮细胞分化过程中，p42mapk及其调节因子受到严格控制，并表明p42mapk是成年肠上皮正常发育中的关键调节分子。
