PI3K/mTOR Signaling Regulates Prostatic Tubulogenesis.
Susmita Ghosh, Hiu Lau, Brian Simons, David Berman, Tamara L Lotan. Johns Hopkins University School of Medicine, Baltimore, MD
Background: The Gleason grading system, one of the most powerful prognosticators in prostatic adenocarcinoma, is a measure of the degree to which tumor cells form tubules. However the signaling pathways that modulate normal and malignant prostatic tubulogenesis remain unclear. Here, we used embryonic prostatic development as a model system to study the role of the oncogenic PI3K/mTOR signaling pathway in the regulation of prostatic tubulogenesis and cell migration.
Design: Urogenital sinuses (UGS) were dissected from E15.5 mice and prostatic branching morphogenesis was initiated in the presence of PI3K/mTOR inhibitors or vehicle. Immunoblotting, immunohistochemistry (IHC) and immunofluorescence (IF) in mice transgenic for AKT-PH-GFP were used to measure PI3K/mTOR activity during prostatic development in vivo and following drug addition in vitro. A novel mesenchyme-free epithelial culture system was used to quantify prostatic epithelial migration during branching. (ER)-ROSA-cre PTENloxp/loxp mice were used to study the effects of PTEN loss of function during tubulogenesis.
Results: Immunoblotting, IHC and IF demonstrated that PI3K is induced and activated in the invading epithelium during prostatic tubulogenesis. UGS organ culture in the presence of LY294002 or wortmannin (PI3K inhibitors) resulted in a significant decrease in epithelial bud number and length. Surprisingly, this decrease in prostatic branching was not due to changes in cellular proliferation or apoptosis. Instead, PI3K inhibition resulted in defective prostate epithelial cell migration, with markedly decreased cellular displacement and speed. Interestingly, simultaneous inhibition of mTORC1 and C2 phenocopied PI3K inhibition, suggesting that mTOR is the essential downstream mediator of PI3K signaling in prostatic tubulogenesis. Remarkably, however, mTORC1 inhibition alone had the opposite effect, increasing bud number and length. Although PTEN loss of function in UGS cultures resulted in increased PI3K signaling, there was no change in prostate branching likely because downstream mTORC1 and C2 activity have opposite and competing effects.
Conclusions: Loss of PTEN frequently results in aberrant PI3K/mTOR signaling during prostatic tumorigenesis. Using embryonic development as a model system, we found that this signaling pathway is required for prostatic epithelial tubulogenesis and cell migration. Significantly, the major downstream effectors of PI3K signaling, mTORC1 and C2, have opposing effects on prostatic tubulogenesis, suggesting that drugs that preferentially inhibit mTORC2 activity may be useful in the treatment of prostate carcinoma.
Tuesday, March 1, 2011 1:45 PM
Platform Session: Section H, Tuesday Afternoon