Department of Biochemistry, School of Medicine, Institute for Tumor Research, Chungbuk National University, Cheongju 361-763, South Korea.
Cancer Science Institute Singapore, National University of Singapore and Institute of Molecular and Cell Biology, 61 Biopolis Drive, Proteos, Singapore 138673, Singapore.
J Biol Chem. 2010 Mar 26;285(13):10122-10129. doi: 10.1074/jbc.M109.071381. Epub 2010 Jan 25.
RUNX3 is a transcription factor that functions as a tumor suppressor. In some cancers, RUNX3 expression is down-regulated, usually due to promoter hypermethylation. Recently, it was found that RUNX3 can also be inactivated by the mislocalization of the protein in the cytoplasm. The molecular mechanisms controlling this mislocalization are poorly understood. In this study, we found that the overexpression of Src results in the tyrosine phosphorylation and cytoplasmic localization of RUNX3. We also found that the tyrosine residues of endogenous RUNX3 are phosphorylated and that the protein is localized in the cytoplasm in Src-activated cancer cell lines. We further showed that the knockdown of Src by small interfering RNA, or the inhibition of Src kinase activity by a chemical inhibitor, causes the re-localization of RUNX3 to the nucleus. Collectively, our results demonstrate that the tyrosine phosphorylation of RUNX3 by activated Src is associated with the cytoplasmic localization of RUNX3 in gastric and breast cancers.
RUNX3 是一种转录因子，作为肿瘤抑制因子发挥作用。在某些癌症中，RUNX3 的表达下调，通常是由于启动子超甲基化。最近发现，RUNX3 也可以通过蛋白质在细胞质中的错误定位而失活。控制这种错误定位的分子机制知之甚少。在这项研究中，我们发现 Src 的过表达导致 RUNX3 的酪氨酸磷酸化和细胞质定位。我们还发现内源性 RUNX3 的酪氨酸残基被磷酸化，并且在 Src 激活的癌细胞系中蛋白质定位于细胞质中。我们进一步表明，通过小干扰 RNA 敲低 Src，或通过化学抑制剂抑制 Src 激酶活性，可导致 RUNX3 重新定位到细胞核中。总之，我们的结果表明，激活的 Src 对 RUNX3 的酪氨酸磷酸化与胃癌和乳腺癌中 RUNX3 的细胞质定位有关。
