Pten loss and RAS/MAPK activation cooperate to promote EMT and prostate cancer metastasis initiated from stem/progenitor cells

PTEN loss or PI3K/AKT signaling pathway activation correlates with human prostate cancer progression and metastasis. However, in preclinical murine models, deletion of Pten alone fails to mimic the significant metastatic burden that frequently accompanies the end stage of human disease. To identify additional pathway alterations that cooperate with PTEN loss in prostate cancer progression, we surveyed human prostate cancer tissue microarrays and found that the RAS/MAPK pathway is significantly elevated both in primary and metastatic lesions. In an attempt to model this event, we crossed conditional activatable K-rasG12D/WT mice with the prostate conditional Pten deletion model we previously generated. Although RAS activation alone cannot initiate prostate cancer development, it significantly accelerated progression caused by PTEN loss, accompanied by epithelial-to-mesenchymal transition (EMT) and macrometastasis with 100% penitence. A novel stem/progenitor subpopulation with mesenchymal characteristics was isolated from the compound mutant prostates, which was highly metastatic upon orthotopic transplantation. Importantly, inhibition of RAS/MAPK signaling by PD325901, a MEK inhibitor, significantly reduced the metastatic progression initiated from transplanted stem/progenitor cells. Collectively, these data indicate that activation of RAS/MAPK signaling serves as a potentiating second hit to alteration of the PTEN/PI3K/AKT axis and co-targeting both pathways is highly effective in preventing the development of metastatic prostate cancers. Murine mutants with prostate specific loss of Pten and K-ras activation (K-rasG12D) under regulation of the probasin promoter developed high grade, invasive prostate cancer. RNA was extracted from dissected prostate lobes from individual mutants with pathology thought to closely mimic human disease. Prostate tissue was subject to RNA extraction and hybridization on Affymetrix cDNA microarrays.

PTEN缺失（PTEN loss）或PI3K/AKT信号通路（PI3K/AKT signaling pathway）激活与人类前列腺癌进展及转移密切相关。然而在临床前小鼠模型中，仅敲除Pten无法模拟人类疾病终末期常伴随的显著转移负荷。为筛选可与PTEN缺失协同促进前列腺癌进展的其他通路异常，我们对人类前列腺癌组织微阵列（tissue microarrays）进行检测后发现，RAS/MAPK信号通路（RAS/MAPK pathway）在原发灶与转移灶中均显著激活。为构建该事件的疾病模型，我们将条件性激活的K-rasG12D/WT小鼠与本课题组此前构建的前列腺条件性Pten敲除模型进行杂交。尽管单独激活RAS无法启动前列腺癌发生，但其可显著加速PTEN缺失介导的肿瘤进展，并伴随上皮间质转化（EMT，epithelial-to-mesenchymal transition）及100%外显率的大转移灶形成。我们从复合突变小鼠的前列腺组织中分离得到具有间质表型的新型干/祖细胞亚群，该亚群经原位移植后展现出高转移能力。值得注意的是，使用MEK抑制剂PD325901抑制RAS/MAPK信号通路，可显著降低移植的干/祖细胞引发的转移进展。综上，本研究数据表明，RAS/MAPK信号通路激活可作为PTEN/PI3K/AKT轴异常的协同第二击，同时靶向两条通路可有效预防转移性前列腺癌的发生。在前列腺珠蛋白启动子（probasin promoter）的调控下，兼具前列腺特异性Pten缺失与K-ras激活（K-rasG12D）的小鼠突变体可形成高级别侵袭性前列腺癌。我们从病理特征高度模拟人类疾病的各突变体的解剖分离前列腺叶中提取RNA，将前列腺组织进行RNA提取后，在Affymetrix cDNA基因芯片上完成杂交实验。