[Figure 5A] This is not associated with an increase in mRNA stability for PTEN message, indicating that BMP-4 is likely inducing PTEN at the transcriptional level

[Figure 5A] This is not associated with an increase in mRNA stability for PTEN message, indicating that BMP-4 is likely inducing PTEN at the transcriptional level. == Results == We found that BMP-4 induces PTEN in E6 and BPH-1 cells and reduces proliferation. Knockdown of PTEN attenuated the growth-inhibiting effects of BMP-4 in these cells. BMP-4 had no effect in PTEN negative-C4-2B cells, but doxacyclin-driven PTEN C4-2B cells responded to BMP-4 with enhanced PTEN and growth inhibition. BMP-4 also increased PTEN protein stability. == Conclusions == BMP signaling induces PTEN expression and sustains PTEN protein expression resulting in inhibition of prostate epithelial cell growth. These data are the first to identify a mechanistic linkage between BMP signaling and PTEN in the prostate, both of which are independently identified as tumor suppressors and suggest possible coordinate dysregulation in prostate cancer. Keywords:Prostate, epithelium, bone-morphogenetic ETS2 protein, phosphatase homologue of tensin analogue, protein stability == INTRODUCTION == Phosphatase homologue oftensin (PTEN) is one of the most commonly associated mutated genes in prostate cancer, and its mutation is usually tightly correlated to poor clinical prognosis.[1] This protein functions as an endogenous intracellular modulator of the phosphoinositide-3-kinase (PI3K)-Akt pathway and therefore plays a central role in regulating proliferation in many epithelial cells.[2] A key regulatory step in this Aranidipine cascade is phosphorylation of phosphoinositide-bisphosphate (PIP2) to generate PIP3by PI3K, resulting in activation of phosphoinositide-dependent kinases (PDK) and activation of Akt by phosphorylation.[2] PTEN acts as a phosphoinositide phosphatase to reverse this reaction and inhibit PI3K-Akt signaling.[2] Therefore reduced expression or function of PTEN in cancer permits unregulated Akt activation and increased tumor cell proliferation.[34] Numerous mitogens and cytokines impinge upon this pathway by activating secondary adaptor molecules such as src, focal adhesion kinase (FAK), and insulin-like receptor substrate (IRS) that initiate the PI3K-Akt signaling cascade.[58] Studies of growth regulatory pathways in the developing prostate have identified a number of important morphogens including fibroblast growth factors, hedgehog ligands, cytokines including interleukins and transforming growth factor beta, Notch, wnt/beta-catenin and the bone morphogenetic proteins (BMPs).[9] The BMPs are members of the TGF-beta superfamily and over 20 BMP ligands have been identified.[10] The BMPs act by binding heterodimers of BMPR type II and type I receptors activating members of the SMAD family of signaling intermediates, most particularly SMADs 1, 5, and 8.[10] The readout of BMP signaling is phosphorylation of SMADs and Aranidipine changes in transcription of specific target genes.[10] Previous studies have shown that this ligands BMP-4 (and its homolog BMP-2) and BMP-7 are expressed in the developing prostate and exert important effects on prostate growth and proliferation.[1112] Interestingly, expression of BMP-2, 4, and 7 ligands, BMP receptors and intracellular signaling components is diminished in prostate cancer as compared to normal tissue, and BMPs have been shown to inhibit prostate cancer cell line proliferation and tumor growth.[1315] Although it is widely accepted that genetic mutation of PTEN can contribute to tumor tumorgenesis, recent studies suggest regulation of PTEN expression and activity may also contribute to tumor growth.[16] For example, studies have shown that PTEN protein expression is reduced in a significant number of breast cancers.[17] Although, the precise mechanism behind reduced PTEN protein levels in these cancers is poorly understood, repression of PTEN expression as well as changes in the activity and stability of PTEN protein have been proposed. Multiple signals could lead to positive or unfavorable modulation of PTEN expression, including TGF signaling, UV radiation, and EGR-1 and PPAR signaling.[1819] Interestingly, Aranidipine BMP signaling has been demonstrated to sustain PTEN expression in colon cancer cells.[20,21] Given the concurrent loss of expression of PTEN and BMP commonly observed in prostate cancer, we sought to investigate a possible mechanistic relationship between these pathways. == MATERIALS AND METHODS == == Cells and culturing conditions == E6 prostate epithelial cells were kind gifts from Dr. David Jarrard, Department of Urology, University of Aranidipine Wisconsin Madison, and were cultured in conditions as previously published.[22] The immortalized cells were screened for HPV16 E6 protein expression by Western blot analysis.