FOXO3a 持续定位于核内可预测乳腺癌不良预后并促进 Akt 磷酸化。

BACKGROUND: The PI3K-Akt signal pathway plays a key role in tumorigenesis and the development of drug-resistance. Cytotoxic chemotherapy resistance is linked to limited therapeutic options and poor prognosis. METHODOLOGY/PRINCIPAL FINDINGS: Examination of FOXO3a and phosphorylated-Akt (P-Akt) expression in breast cancer tissue microarrays showed nuclear FOXO3a was associated with lymph node positivity (p = 0.052), poor prognosis (p = 0.014), and P-Akt expression in invasive ductal carcinoma. Using tamoxifen and doxorubicin-sensitive and -resistant breast cancer cell lines as models, we found that doxorubicin- but not tamoxifen-resistance is associated with nuclear accumulation of FOXO3a, consistent with the finding that sustained nuclear FOXO3a is associated with poor prognosis. We also established that doxorubicin treatment induces proliferation arrest and FOXO3a nuclear relocation in sensitive breast cancer cells. Induction of FOXO3a activity in doxorubicin-sensitive MCF-7 cells was sufficient to promote Akt phosphorylation and arrest cell proliferation. Conversely, knockdown of endogenous FOXO3a expression reduced PI3K/Akt activity. Using MDA-MB-231 cells, in which FOXO3a activity can be induced by 4-hydroxytamoxifen, we showed that FOXO3a induction up-regulates PI3K-Akt activity and enhanced doxorubicin resistance. However FOXO3a induction has little effect on cell proliferation, indicating that FOXO3a or its downstream activity is deregulated in the cytotoxic drug resistant breast cancer cells. Thus, our results suggest that sustained FOXO3a activation can enhance hyperactivation of the PI3K/Akt pathway. CONCLUSIONS/SIGNIFICANCE: Together these data suggest that lymph node metastasis and poor survival in invasive ductal breast carcinoma are linked to an uncoupling of the Akt-FOXO3a signaling axis. In these breast cancers activated Akt fails to inactivate and re-localize FOXO3a to the cytoplasm, and nuclear-targeted FOXO3a does not induce cell death or cell cycle arrest. As such, sustained nuclear FOXO3a expression in breast cancer may culminate in cancer progression and the development of an aggressive phenotype similar to that observed in cytotoxic chemotherapy resistant breast cancer cell models.

背景：PI3K-Akt 信号通路在肿瘤发生和耐药发展中起着关键作用。细胞毒性化疗耐药与治疗选择有限和预后不良有关。

方法/主要发现：在乳腺癌组织微阵列中检查 FOXO3a 和磷酸化-Akt（P-Akt）的表达，发现核 FOXO3a 与淋巴结阳性（p=0.052）、预后不良（p=0.014）以及浸润性导管癌中的 P-Akt 表达相关。使用他莫昔芬和多柔比星敏感和耐药的乳腺癌细胞系作为模型，我们发现多柔比星而不是他莫昔芬耐药与 FOXO3a 的核积累有关，这与持续核 FOXO3a 与预后不良相关的发现一致。我们还发现，多柔比星处理诱导敏感乳腺癌细胞增殖停滞和 FOXO3a 核重定位。在多柔比星敏感的 MCF-7 细胞中诱导 FOXO3a 活性足以促进 Akt 磷酸化和抑制细胞增殖。相反，内源性 FOXO3a 表达的敲低会降低 PI3K/Akt 活性。使用 MDA-MB-231 细胞，其中 FOXO3a 活性可以被 4-羟基他莫昔芬诱导，我们表明 FOXO3a 诱导上调 PI3K-Akt 活性并增强多柔比星耐药性。然而，FOXO3a 诱导对细胞增殖几乎没有影响，表明在细胞毒性药物耐药的乳腺癌细胞中，FOXO3a 或其下游活性被失调。因此，我们的结果表明，持续的 FOXO3a 激活可以增强 PI3K/Akt 途径的过度激活。

结论/意义：总之，这些数据表明，浸润性导管乳腺癌中的淋巴结转移和生存不良与 Akt-FOXO3a 信号轴的解偶联有关。在这些乳腺癌中，激活的 Akt 未能使 FOXO3a 失活并将其重新定位到细胞质中，而核靶向的 FOXO3a 不会诱导细胞死亡或细胞周期停滞。因此，乳腺癌中持续的核 FOXO3a 表达可能最终导致癌症进展，并发展出类似于在细胞毒性化疗耐药乳腺癌细胞模型中观察到的侵袭性表型。