Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Oncogene. 2012 Feb 16;31(7):897-906. doi: 10.1038/onc.2011.284. Epub 2011 Jul 11.
The ubiquitously expressed 14-3-3 proteins regulate many pathways involved in transformation. Previously, we found that 14-3-3ζ overexpression increased Akt phosphorylation in human mammary epithelial cells. Here, we investigated the clinical relevance and molecular mechanism of 14-3-3ζ-overexpression-mediated Akt phosphorylation, and its potential impact on breast cancer progression. We found that 14-3-3ζ overexpression was significantly (P=0.005) associated with increased Akt phosphorylation in human breast tumors. Additionally, 14-3-3ζ overexpression combined with strong Akt phosphorylation was significantly (P=0.01) associated with increased cancer recurrence in patients. In contrast, knockdown of 14-3-3ζ expression by small interfering RNA in cancer cell lines and tumor xenografts reduced Akt phosphorylation. Furthermore, 14-3-3ζ enhanced Akt phosphorylation through activation of phosphoinositide 3-kinase (PI3K). Mechanistically, 14-3-3ζ bound to the p85 regulatory subunit of PI3K and increased PI3K translocation to the cell membrane. A single 14-3-3-binding motif encompassing serine 83 on p85 is largely responsible for 14-3-3ζ-mediated p85 binding and PI3K/Akt activation. Mutation of serine 83 to alanine on p85 inhibited 14-3-3ζ binding to the p85 subunit of PI3K, reduced PI3K membrane localization and activation, impeded anchorage-independent growth and enhanced stress-induced apoptosis. These findings revealed a novel mechanism by which 14-3-3ζ overexpression activates PI3K, a key node in the mitogenic signaling network known to promote malignancies in many cell types.
14-3-3 蛋白广泛表达，调节多种转化相关途径。先前，我们发现 14-3-3ζ 过表达可增加人乳腺上皮细胞中 Akt 的磷酸化。在此，我们研究了 14-3-3ζ 过表达介导的 Akt 磷酸化的临床相关性和分子机制，及其对乳腺癌进展的潜在影响。我们发现，14-3-3ζ 过表达与人乳腺肿瘤中 Akt 磷酸化的增加显著相关（P=0.005）。此外，14-3-3ζ 过表达与 Akt 磷酸化强阳性相结合，与患者癌症复发显著相关（P=0.01）。相反，在癌细胞系和肿瘤异种移植中，通过小干扰 RNA 敲低 14-3-3ζ 表达可降低 Akt 磷酸化。此外，14-3-3ζ 通过激活磷脂酰肌醇 3-激酶（PI3K）增强 Akt 磷酸化。在机制上，14-3-3ζ 与 PI3K 的 p85 调节亚基结合，并增加 PI3K 向细胞膜的易位。p85 上丝氨酸 83 上的单个 14-3-3 结合基序主要负责 14-3-3ζ 介导的 p85 结合和 PI3K/Akt 激活。p85 上丝氨酸 83 突变为丙氨酸可抑制 14-3-3ζ 与 PI3K p85 亚基的结合，减少 PI3K 膜定位和激活，阻碍非锚定依赖性生长，并增强应激诱导的细胞凋亡。这些发现揭示了 14-3-3ζ 过表达激活 PI3K 的新机制，PI3K 是已知在许多细胞类型中促进恶性肿瘤的有丝分裂信号网络中的关键节点。
