Department of Pathology, Vanderbilt University Medical Center, Nashville, TN, USA.
BMC Cancer. 2010 Jun 1;10:248. doi: 10.1186/1471-2407-10-248.
The serine/threonine kinase PIM1 has been implicated as an oncogene in various human cancers including lymphomas, gastric, colorectal and prostate carcinomas. In mouse models, Pim1 is known to cooperate with c-Myc to promote tumorigenicity. However, there has been limited analysis of the tumorigenic potential of Pim1 overexpression in benign and malignant human prostate cancer cells in vivo.
We overexpressed Pim1 in three human prostate cell lines representing different disease stages including benign (RWPE1), androgen-dependent cancer (LNCaP) and androgen-independent cancer (DU145). We then analyzed in vitro and in vivo tumorigenicity as well as the effect of Pim1 overexpression on c-MYC transcriptional activity by reporter assays and gene expression profiling using an inducible MYC-ER system. To validate that Pim1 induces tumorigenicity and target gene expression by modulating c-MYC transcriptional activity, we inhibited c-MYC using a small molecule inhibitor (10058-F4) or RNA interference.
Overexpression of Pim1 alone was not sufficient to convert the benign RWPE1 cell to malignancy although it enhanced their proliferation rates when grown as xenografts in vivo. However, Pim1 expression enhanced the in vitro and in vivo tumorigenic potentials of the human prostate cancer cell lines LNCaP and DU145. Reporter assays revealed increased c-MYC transcriptional activity in Pim1-expressing cells and mRNA expression profiling demonstrated that a large fraction of c-MYC target genes were also regulated by Pim1 expression. The c-MYC inhibitor 10058-F4 suppressed the tumorigenicity of Pim1-expressing prostate cancer cells. Interestingly, 10058-F4 treatment also led to a reduction of Pim1 protein but not mRNA. Knocking-down c-MYC using short hairpin RNA reversed the effects of Pim1 on Pim1/MYC target genes.
Our results suggest an in vivo role of Pim1 in promoting prostate tumorigenesis although it displayed distinct oncogenic activities depending on the disease stage of the cell line. Pim1 promotes tumorigenicity at least in part by enhancing c-MYC transcriptional activity. We also made the novel discovery that treatment of cells with the c-MYC inhibitor 10058-F4 leads to a reduction in Pim1 protein levels.
丝氨酸/苏氨酸激酶 PIM1 已被认为是多种人类癌症（包括淋巴瘤、胃癌、结直肠癌和前列腺癌）的致癌基因。在小鼠模型中，已知 Pim1 与 c-Myc 合作促进肿瘤发生。然而，在体内，对 Pim1 过表达在良性和恶性人类前列腺癌细胞中的致瘤潜能的分析有限。
我们在三种代表不同疾病阶段的人前列腺细胞系中过表达 Pim1，包括良性（RWPE1）、雄激素依赖性癌症（LNCaP）和雄激素非依赖性癌症（DU145）。然后，我们通过报告基因分析和使用可诱导 MYC-ER 系统的基因表达谱分析，分析体外和体内的致瘤性，以及 Pim1 过表达对 c-MYC 转录活性的影响。为了验证 Pim1 通过调节 c-MYC 转录活性诱导致瘤性和靶基因表达，我们使用小分子抑制剂（10058-F4）或 RNA 干扰抑制 c-MYC。
Pim1 的单独过表达本身不足以使良性 RWPE1 细胞转化为恶性肿瘤，尽管它增强了它们在体内异种移植时的增殖率。然而，Pim1 表达增强了人前列腺癌细胞系 LNCaP 和 DU145 的体外和体内致瘤潜能。报告基因分析显示，在表达 Pim1 的细胞中 c-MYC 转录活性增加，mRNA 表达谱分析表明，c-MYC 靶基因的很大一部分也受 Pim1 表达的调节。c-MYC 抑制剂 10058-F4 抑制了表达 Pim1 的前列腺癌细胞的致瘤性。有趣的是，10058-F4 处理还导致 Pim1 蛋白减少，但 mRNA 不变。使用短发夹 RNA 敲低 c-MYC 逆转了 Pim1 对 Pim1/MYC 靶基因的影响。
我们的结果表明 Pim1 在体内促进前列腺肿瘤发生中的作用，尽管它根据细胞系的疾病阶段表现出不同的致癌活性。Pim1 通过增强 c-MYC 转录活性促进致瘤性。我们还发现了一个新的发现，即用 c-MYC 抑制剂 10058-F4 处理细胞会导致 Pim1 蛋白水平降低。
