Harder K W, Moller N P, Peacock J W, Jirik F R
Centre for Molecular Medicine and Therapeutics and the Department of Medicine, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada.
J Biol Chem. 1998 Nov 27;273(48):31890-900. doi: 10.1074/jbc.273.48.31890.
The roles of protein-tyrosine phosphatases (PTPs) in processes such as cell growth and adhesion are poorly understood. To explore the ability of specific PTPs to regulate cell signaling pathways initiated by stimulation of growth factor receptors, we expressed the receptor-like PTP, PTPalpha, in A431 epidermoid carcinoma cells. These cells express high levels of the epidermal growth factor (EGF) receptor and proliferate in response to the autocrine production of transforming growth factor-alpha. Conversely, EGF stimulation of A431 cells in vitro leads to growth inhibition and triggers the rapid detachment of these cells from the substratum. Although PTPalpha expression did not alter the growth characteristics of either unstimulated or EGF-stimulated cells, this phosphatase was associated with increased cell-substratum adhesion. Furthermore, PTPalpha-expressing A431 cells were strikingly resistant to EGF-induced cell rounding. Overexpression of PTPalpha in A431 cells was associated with the dephosphorylation/activation of specific Src family kinases, suggesting a potential mechanism for the observed alteration in A431 cell-substratum adhesion. Src kinase activation was dependent on the D1 catalytic subunit of PTPalpha, and there was evidence of association between PTPalpha and Src kinase(s). PTPalpha expression also led to increased association of Src kinase with the integrin-associated focal adhesion kinase, pp125(FAK). In addition, paxillin, a Src and/or pp125(FAK) substrate, displayed increased levels of tyrosine phosphorylation in PTPalpha-expressing cells and was associated with elevated amounts of Csk. In view of these alterations in focal adhesion-associated molecules in PTPalpha-expressing A431 cells, as well as the changes in adhesion demonstrated by these cells, we propose that PTPalpha may have a role in regulating cell-substratum adhesion.
蛋白酪氨酸磷酸酶（PTP）在细胞生长和黏附等过程中的作用尚不清楚。为了探究特定PTP调节由生长因子受体刺激引发的细胞信号通路的能力，我们在A431表皮癌细胞中表达了受体样PTP，即PTPα。这些细胞表达高水平的表皮生长因子（EGF）受体，并因自分泌转化生长因子-α而增殖。相反，体外EGF刺激A431细胞会导致生长抑制并触发这些细胞从基质上快速脱离。尽管PTPα的表达并未改变未刺激或EGF刺激细胞的生长特性，但这种磷酸酶与细胞-基质黏附增加有关。此外，表达PTPα的A431细胞对EGF诱导的细胞变圆具有显著抗性。A431细胞中PTPα的过表达与特定Src家族激酶的去磷酸化/激活有关，这表明了A431细胞-基质黏附改变的潜在机制。Src激酶的激活依赖于PTPα的D1催化亚基，并且有证据表明PTPα与Src激酶之间存在关联。PTPα的表达还导致Src激酶与整合素相关的粘着斑激酶pp125（FAK）的关联增加。此外，桩蛋白是一种Src和/或pp125（FAK）底物，在表达PTPα的细胞中显示出酪氨酸磷酸化水平升高，并且与Csk含量增加有关。鉴于表达PTPα的A431细胞中粘着斑相关分子的这些改变，以及这些细胞所表现出的黏附变化，我们提出PTPα可能在调节细胞-基质黏附方面发挥作用。
