Function and regulatory mechanisms of the candidate tumor suppressor receptor protein tyrosine phosphatase gamma (PTPRG) in breast cancer cells.
Function and regulatory mechanisms of the candidate tumor suppressor receptor protein tyrosine phosphatase gamma (PTPRG) in breast cancer cells.
复制标题
DOI：
--
复制
发表时间：
2010-06
影响因子：
2
通讯作者：
S. Shu;Y. Sugimoto;Suling Liu;Hsiang-lin Chang;Weiping Ye;Li‐Shu Wang;Yi-Wen Huang;P. Yan;Young C. Lin
中科院分区：
文献类型：
--
作者：
S. Shu;Y. Sugimoto;Suling Liu;Hsiang-lin Chang;Weiping Ye;Li‐Shu Wang;Yi-Wen Huang;P. Yan;Young C. Lin
蛋白质磷酸化是细胞信号传导中的重要步骤之一，异常磷酸化是人类癌症中的常见事件。受体型蛋白酪氨酸磷酸酶γ（PTPRG）在正常乳腺中的表达比乳腺肿瘤组织高约50-60%。PTPRG过表达抑制乳腺癌细胞的锚定非依赖性生长和增殖。为了了解PTPRG的肿瘤抑制特性，我们在无胸腺小鼠模型中研究了其肿瘤抑制功能，并评估了可能调节其在乳腺癌细胞中表达的因素。材料与方法为研究PTPRG在体内的功能，将过表达PTPRG的MCF-7细胞植入裸鼠体内。对于体外研究，检查细胞周期调节剂的蛋白水平、细胞周期再进入和细胞外信号调节蛋白激酶1/2（ERK 1/2）的磷酸化水平。此外，进行甲基化测定以研究PTPRG启动子上的表观遗传修饰。结果与单纯转染载体的MCF-7细胞相比，携带过表达PTPRG的MCF-7细胞的无胸腺裸鼠的肿瘤负荷降低。当在体外系统中研究这两种细胞系时，与仅用载体转染的细胞相比，在过表达PTPRG的MCF-7细胞中检测到细胞周期调节因子p21（cip）和p27（kip）的mRNA和蛋白水平升高。同样，PTPRG的过表达也延迟了血清饥饿后乳腺癌细胞重新进入细胞周期，并降低了MCF-7细胞中ERK 1/2的磷酸化水平。此外，乳腺癌细胞系（包括SK-Br-3）中PTPRG启动子的甲基化测定揭示了异常的甲基化模式。当SK-Br-3和MCF-7细胞用脱氧-5-氮杂胞苷（DAC）和阿司他丁A（TSA）处理时，这些化合物重新激活PTPRG的表达，表明其表达受到表观遗传控制。结论PTPRG可抑制乳腺癌的形成，PTPRG可能通过ERK 1/2途径上调p21（cip）和p27（kip）蛋白的表达。该研究还显示了乳腺癌细胞系中甲基化介导的PTPRG沉默。这些数据表明，PTPRG表现出乳腺肿瘤抑制因子的特征。
BACKGROUND Protein phosphorylation is one of the essential steps in cell signaling, and aberrant phosphorylation is a common event in human cancer. The expression of receptor type protein tyrosine phosphatase gamma (PTPRG) in normal breast is found to be approximately 50-60% higher than that of breast tumor tissue. Overexpression of PTPRG inhibits anchorage-independent growth and proliferation of breast cancer cells. To understand the tumor suppression characteristics of PTPRG, we studied its tumor suppressive function in an athymic mouse model and evaluated factors that can potentially regulate its expression in breast cancer cells. MATERIALS AND METHODS To investigate the function of PTPRG in vivo, athymic nude mice were implanted with MCF-7 cells overexpressing PTPRG. For in vitro study, protein levels of cell cycle regulators, cell cycle re-entry, and the phosphorylation levels of extracellular signal-regulated protein kinases 1/2 (ERK1/2) were examined. In addition, methylation assays were conducted to investigate the epigenetic modification on the promoter of PTPRG. RESULTS Athymic nude mice bearing MCF-7 cells overexpressing PTPRG showed a reduction in tumor burden in comparison to animals implanted with MCF-7 cells transfected with vector alone. When these two cell lines were studied in an in vitro system, elevated mRNA and protein levels of cell cycle regulators, p21(cip) and p27(kip) were detected in MCF-7 cells overexpressing PTPRG compared to cells transfected with vector alone. Similarly, overexpression of PTPRG also delayed the re-entry of breast cancer cells into the cell cycle after serum starvation, and reduced the phosphorylation levels ERK1/2 in MCF-7 cells. In addition, methylation assays in PTPRG promoter in breast cancer cell lines (including SK-Br-3) revealed an aberrant methylation pattern. When SK-Br-3 and MCF-7 cells were treated with deoxy-5-azacytidine (DAC) and trichostatin A (TSA), these compounds reactivated the expression of PTPRG, suggesting an epigenetic control on its expression. CONCLUSION Our results indicated that PTPRG inhibited breast tumor formation in vivo; PTPRG may up-regulate p21(cip) and p27(kip) proteins through the ERK1/2 pathway. This study also showed methylation-mediated silencing of PTPRG in breast cancer cell lines. These data indicate that PTPRG exhibits the characteristics of a breast tumor suppressor.