Holm Caroline, Rayala Suresh, Jirström Karin, Stål Olle, Kumar Rakesh, Landberg Göran
Division of Pathology, Department of Laboratory Medicine, Lund University, Malmö, Sweden.
J Natl Cancer Inst. 2006 May 17;98(10):671-80. doi: 10.1093/jnci/djj185.
p21-activated kinase 1 (Pak1) phosphorylates many proteins in both normal and transformed cells. Its ability to phosphorylate and thereby activate the estrogen receptor alpha (ERalpha) potentially limits the effectiveness of antiestrogen treatment in breast cancer. Here we studied associations between Pak1 expression and subcellular localization in tumor cells and tamoxifen resistance.
Pak1 protein expression was evaluated in 403 primary breast tumors from premenopausal patients who had been randomly assigned to 2 years of adjuvant tamoxifen or no treatment. Tamoxifen response was evaluated by comparing recurrence-free survival in relation to Pak1 and ERalpha expression in untreated versus tamoxifen-treated patients. Tamoxifen responsiveness of human MCF-7 breast cancer cells that inducibly expressed constitutively active Pak1 or that transiently overexpressed wild-type Pak1 (Wt-Pak1) or Pak1 that lacked functional nuclear localization signals (Pak1DeltaNLS) was evaluated by analyzing cyclin D1 promoter activation and protein levels as markers for ERalpha activation. The response to tamoxifen in relation to Pak1 expression was analyzed in naturally tamoxifen-resistant Ishikawa human endometrial cancer cells. All statistical tests were two-sided.
Among patients who had ERalpha-positive tumors with low Pak1 expression, those treated with tamoxifen had better recurrence-free survival than those who received no treatment (hazard ratio [HR] = 0.502, 95% confidence interval [CI] = 0.331 to 0.762; P = .001) whereas there was no difference in recurrence-free survival between treatment groups for patients whose tumors had high cytoplasmic (HR = 0.893, 95% CI = 0.420 to 1.901; P = .769) or any nuclear Pak1 expression (HR = 0.955, 95% CI = 0.405 to 2.250; P = .916). In MCF-7 cells, overexpression of Wt-Pak1, but not of Pak1DeltaNLS, compromised tamoxifen response by stimulating cyclin D1 expression. Treatment of Ishikawa cells with tamoxifen led to an increase in the amount of nuclear Pak1 and Pak1 kinase activity, suggesting that tamoxifen, to some extent, regulates Pak1 expression.
Our data support a role for Pak1, particular Pak1 localized to the nucleus, in ERalpha signaling and in tamoxifen resistance.
p21激活激酶1（Pak1）可使正常细胞和转化细胞中的多种蛋白质磷酸化。其磷酸化并激活雌激素受体α（ERα）的能力可能会限制抗雌激素治疗在乳腺癌中的疗效。在此，我们研究了肿瘤细胞中Pak1表达和亚细胞定位与他莫昔芬耐药性之间的关联。
对403例绝经前患者的原发性乳腺肿瘤进行Pak1蛋白表达评估，这些患者被随机分配接受2年辅助性他莫昔芬治疗或不接受治疗。通过比较未治疗组和他莫昔芬治疗组患者中与Pak1和ERα表达相关的无复发生存率来评估他莫昔芬反应。通过分析细胞周期蛋白D1启动子激活和蛋白水平作为ERα激活的标志物，评估可诱导表达组成型活性Pak1或瞬时过表达野生型Pak1（Wt-Pak1）或缺乏功能性核定位信号的Pak1（Pak1DeltaNLS）的人MCF-7乳腺癌细胞对他莫昔芬的反应性。在天然对他莫昔芬耐药的石川人子宫内膜癌细胞中分析与Pak1表达相关的他莫昔芬反应。所有统计检验均为双侧检验。
在ERα阳性且Pak1表达低的肿瘤患者中，接受他莫昔芬治疗的患者比未接受治疗的患者无复发生存率更好（风险比[HR]=0.502，95%置信区间[CI]=0.331至0.762；P=0.001），而肿瘤具有高细胞质（HR=0.893，95%CI=0.420至1.901；P=0.769）或任何核Pak1表达的患者，治疗组之间的无复发生存率没有差异（HR=0.955，95%CI=0.405至2.250；P=0.916）。在MCF-7细胞中，Wt-Pak1而非Pak1DeltaNLS的过表达通过刺激细胞周期蛋白D1表达而损害了他莫昔芬反应。用他莫昔芬处理石川细胞导致核Pak1量和Pak1激酶活性增加，这表明他莫昔芬在一定程度上调节Pak1表达。
我们的数据支持Pak1，特别是定位于细胞核的Pak1，在ERα信号传导和他莫昔芬耐药中发挥作用。
