Mishra S, Hamburger A W
Department of Pathology, University of Maryland Cancer Center, Baltimore 21201.
Carcinogenesis. 1993 Feb;14(2):269-73. doi: 10.1093/carcin/14.2.269.
Protein tyrosine phosphatases (PTPases) are potential tumor suppressor proteins which reverse the effects of protein tyrosine kinases (PTKs). We hypothesized that the induction of PTPase activity by the nutritional agent O-phospho-L-tyrosine (P-Tyr), a broad PTPase substrate, could potentially enhance total cellular PTPase activity and inhibit cell growth. In this study, we report that P-Tyr inhibited the growth of MDA-MB 468 cells in a dose-dependent fashion. P-Tyr incubation increased total cellular PTPase activity in MDA-MB 468 breast carcinoma cells. The increase of PTPase activity, as measured by a standard radioactive assay for PTPases, occurred within 10 min of P-Tyr incubation and was dependent on the concentration and time of incubation with P-Tyr. The increased PTPase activity in P-Tyr treated cells was also evident from a non-isotopic PTPase assay involving the dephosphorylation of epidermal growth factor receptor (EGFR). Epidermal growth factor (EGF)-mediated tyrosine phosphorylation of EGFR was decreased in situ in a time- and dose-dependent manner in P-Tyr-treated cells. Orthovanadate (100 microM for 4 h) inhibited this decrease, implicating the role of cellular PTPase in P-Tyr-mediated control of EGFR tyrosine phosphorylation. Further, EGFR kinase activity was found to be decreased in P-Tyr-treated cells. We conclude that P-Tyr may inhibit cell growth by decreasing cellular tyrosine phosphorylation. Both a decrease in activity of the EGFR kinase and increases in PTPase activity may have accounted for the growth inhibiting property of P-Tyr.
蛋白质酪氨酸磷酸酶（PTPases）是一类潜在的肿瘤抑制蛋白，可逆转蛋白质酪氨酸激酶（PTKs）的作用。我们推测，营养物质O-磷酸-L-酪氨酸（P-Tyr）作为一种广泛的PTPase底物，诱导PTPase活性可能会增强细胞总PTPase活性并抑制细胞生长。在本研究中，我们报告P-Tyr以剂量依赖的方式抑制MDA-MB 468细胞的生长。用P-Tyr孵育可增加MDA-MB 468乳腺癌细胞中的细胞总PTPase活性。通过PTPases的标准放射性测定法测得的PTPase活性增加，在P-Tyr孵育10分钟内即可出现，且依赖于P-Tyr的孵育浓度和时间。从涉及表皮生长因子受体（EGFR）去磷酸化的非同位素PTPase测定中也可明显看出，P-Tyr处理的细胞中PTPase活性增加。在P-Tyr处理的细胞中，表皮生长因子（EGF）介导的EGFR酪氨酸磷酸化在原位呈时间和剂量依赖性降低。原钒酸盐（100 microM，处理4小时）可抑制这种降低，这表明细胞PTPase在P-Tyr介导的EGFR酪氨酸磷酸化控制中发挥作用。此外，发现P-Tyr处理的细胞中EGFR激酶活性降低。我们得出结论，P-Tyr可能通过降低细胞酪氨酸磷酸化来抑制细胞生长。EGFR激酶活性的降低和PTPase活性的增加可能共同导致了P-Tyr的生长抑制特性。
