Transgenic Expression of Polyomavirus Middle T Antigen in the Mouse Prostate Gives Rise to Carcinoma

Abstract

The middle T (MT) antigen of polyomavirus has provided fundamental insights into the regulation of mammalian cell growth in vitro and important animal models for the analysis of tumor induction. The mouse mammary tumor virus (MMTV)-MT model of breast cancer has been important for probing the cellular signaling pathways in mammary tumorigenesis. MT itself has no intrinsic enzymatic activity but, rather, transforms by binding to and activating key intracellular signaling molecules, phosphatidylinositol 3-kinase (PI3-kinase) being the best studied of these. Thus, MT mimics a constitutively activated receptor tyrosine kinase (RTK). Our recent work suggests that MT signaling, like that of RTKs, is often quite dependent on cellular context in vitro. Here, we examine contextual effects on signaling in animal models as well. In this study, we generated transgenic mice in which MT is expressed in the mouse prostate under the control of an (ARR)2-Probasin promoter. All male transgenic mice displayed mouse prostatic intraepithelial neoplasia In the male population of the United States, prostate cancer is the second most commonly diagnosed cancer after dermatologic cancer. Typically developing slowly with age, it ranks second among all cancers as a cause of mortality in men in the United States. Considerable insight concerning the effects of genetic alterations on prostate tissue has been gleaned from a number of genetically engineered mouse models (GEMs). For example, the activation of receptor tyrosine kinase (RTK) pathways has been modeled via transgenic mice expressing Fgf8b (15, 56), Neu (34), and Erbb2 (6). Loss-of-function models for tumor suppressor genes include Nkx3.1 (30) and PTEN (11,61,63,68). Models of oncogene expression include the expression of Akt (40), PIK3CB (32), c-myc (14), H-ras (52), and two models expressing simian virus 40 (SV40) large T antigen (the transgenic adenocarcinoma of mouse prostate [TRAMP] model [22] and the large probasin-large T antigen [LPB-Tag] model [41]). The resulting lesions vary according to the target gene, displaying histological abnormalities ranging from hyperplasia to metastatic cancer. Tumor development in most transgenic mice created via the expression of a single gene is limited to hyperplasia or mouse prostatic intraepithelial neoplasia (mPIN), while high levels of expression of myc and SV40 T antigen resulted in metastatic cancers (14,22). Gene deletion of Nkx3.1 or PTEN did not result in metastatic adenocarcinoma (11,30,61,63) except in one PTEN study (68). However, double knockout models, such as the deletion of PTEN together with p53 (9), p27 (10), or Nkx3.1 (31), develop more aggressive phenotypes, suggesting that multiple genetic hits may be required to accelerate prostate cancer progression initiated by PTEN loss.Polyomavirus (PyV) middle T antigen (MT) is one of three early gene products encoded by the single early mRNA of this small DNA tumor virus (21, 51). It is the only protein encoded by the PyV genome that induces transformation in vitro. MT utilizes a hy...

IL4 Receptor ILR4α Regulates Metastatic Colonization by Mammary Tumors through Multiple Signaling Pathways

“…7B). The R221a cells express the middle T oncoprotein, a strong driver of constitutive PI3K/Akt and Src kinase activity, which would be unaffected by LY294002 treatment [25]. These results confirm previous reports that activation of Akt in response to IL4 is cell type/context dependent [5, 12].…”

The Phosphatidylinositol 3-Kinase (PI3K) Isoform Dependence of Tumor Formation Is Determined by the Genetic Mode of PI3K Pathway Activation Rather than by Tissue Type

“…Previous work from our laboratories showed that prostate-specific expression of polyomavirus MT in the mouse leads to prostate intraepithelial neoplasia (PIN) in the dorsolateral prostate (DLP) and ventral prostate (VP) lobes. This phenotype can be observed in animals as young as 8 weeks of age and progresses throughout the animal's lifetime, ultimately leading to invasion (10).…”

“…As noted earlier, MT tumorigenesis in the breast requires p110␣. We have recently reported a prostate cancer model driven by wildtype MT (10). Here we demonstrate the pivotal role of the PI3K pathway by showing that the loss of PI3K signaling causes significantly delayed tumor growth.…”

Prostate Microbiota and Prostate Cancer: A New Trend in Treatment

“…And the transcriptional activities of p65 and IkBa genes in infected prostate epithelial cells were significantly higher than those in uninfected cells, indicating that the NF-kB signaling pathway was involved in the occurrence of prostate cancer in the early stage of inflammation, and the activation of NF-kB was time-dependent with the stimulation of inflammation (68,73). In an animal experiment, mice infected with polyomavirus developed prostatic intraepithelial neoplasia on the ventral and dorsal sides of the prostate, and transcriptional map analysis showed regulation of multiple pathways, including NF-kB (87). In other words, the use of some means to regulate the activity of NF-kB may lead to the loss of the cancerous potential of prostate cells.…”