Forms Of PTEN Research Articles

The protein phosphatase activity of PTEN is essential for regulating neural stem cell differentiation.

BackgroundThe tumor suppressor gene Phosphatase and tensin homolog (PTEN) is highly expressed in neural progenitor cells (NPCs) and plays an important role in development of the central nervous system. As a dual-specificity phosphatase, the loss of PTEN phosphatase activity has been linked to various diseases.ResultsHere we report that the protein phosphatase activity of Pten is critical for regulating differentiation of neural progenitor cells. First we found that deletion of Pten promotes neuronal differentiation. To determine whether the protein or lipid phosphatase activity is required for regulating neuronal differentiation, we generated phosphatase domain-specific Pten mutations. Interestingly, only expression of protein phosphatase-deficient mutant Y138L could mimic the effect of knocking down Pten, suggesting the protein phosphatase of Pten is critical for regulating NPC differentiation. Importantly, we showed that the wild-type and lipid phosphatase mutant (G129E) forms of Pten are able to rescue neuronal differentiation in Pten knockout NPCs, but mutants containing protein phosphatase mutant cannot. We further found that Pten-dependent dephosphorylation of CREB is critical for neuronal differentiation.ConclusionOur data indicate that the protein phosphatase activity of PTEN is critical for regulating differentiation of NSCs during cortical development.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-015-0114-1) contains supplementary material, which is available to authorized users.

Abstract 5222: A novel mechanism of microenvironment-mediated drug resistance in BRAF V600E melanoma with loss of PTEN

Abstract Despite recent success of the BRAF kinase inhibitor vemurafenib in the clinic, nearly all of those treated follow a course in which initial tumor regression was followed by eventual relapse, which constitutes a major barrier to long-term therapeutic management of melanoma. We have identified a novel mechanism of microenvironment-mediated drug resistance that arises from the release of TGFβ from melanomas that lack PTEN expression leading to the recruitment of host fibroblasts and the generation of a protective microenvironment through autocrine and paracrine fibronectin secretion facilitating therapeutic escape. Preliminary studies show that BRAF V600E mutant melanoma cell lines that lacked PTEN expression dramatically increased their secretion of TGF-β following vemurafenib treatment, as detected by western blot, immunofluorescence and ELISA assays. Furthermore, autocrine TGFβ secretion initiated with vemurafinib treatment stimulated the upregulation and secretion of fibronectin in PTEN- cells. The vemurafenib-mediated ECM remodeling in this case was dependent upon autocrine TGFβ signaling and could be attenuated following pre-treatment with the TGFβ receptor kinase inhibitor SB505124 or by siRNA knockdown of TGFβ receptor I. A mass spectrometry based phospho-proteomic screen in conjunction with innovative network modeling approaches suggested that increased integrin α5β1 signaling was a key adaptive response of PTEN- melanoma cells to BRAF inhibitor therapy. The importance of increased fibronectin expression and integrin α5β1 signaling in the therapeutic escape of PTEN- melanoma cells was confirmed by the significant increases in vemurafenib-induced apoptosis observed following siRNA knockdown of either integrin α5, β1, or fibronectin expression. A mass spectrometry screen (LC-MRM) of 18 BH3 proteins demonstrated Mcl-1 and Bak to be critical apoptosis regulators in the microenvironment-mediated drug resistance response. The importance of PTEN loss and Mcl-1 downregulation in therapeutic escape was validated in PTEN- melanoma cell lines expressing doxycycline inducible forms of PTEN, lipid phosphatase mutant PTEN and Mcl-1. Novel organotypic co-culture models were developed to demonstrate that TGF-β released from PTEN- melanoma cell lines activated host fibroblasts leading to the attenuation of drug response in the tumor cells. Our overall hypothesis is that BRAF inhibition remodels both the melanoma and host microenvironments to provide a protective “sanctuary” for the minor populations of melanoma cells that escape therapy. We postulate that tumor eradication can only be achieved by a dual therapeutic strategy that targets both the bulk tumor and the microenvironment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5222. doi:1538-7445.AM2012-5222

Testosterone improves the transition of primary oocytes in artificial maturation eels (Anguilla japonica) by altering ovarian PTEN expression

In mammals, androgens appear to enhance the development of primary ovarian follicles, but PI3K (phosphoinositide 3-kinases) pathway is well recognized as one of the critical pathways in early follicular development. Roles of the PI3K were revealed by deletion of PTEN (phosphatase and tensin homolog on chromosome 10). PTEN is demonstrated to play an important role in the early stage of follicle development. In the Japanese eel, two forms of PTEN have been cloned, but what their functions on the development of early ovarian follicles are still not clear. The natural blockage and inducible of ovarian development was a benefit to address this question in the eel. Testosterone (T) shows to ameliorate the early ovarian development in the eel. The aims of this study were to elucidate the two forms of PTEN by cellular and physiological criteria and to study the effects of T on the ovarian PTEN production in the exogenous pituitary extracts-stimulated eel. Our results suggested that two forms of PTEN are existing in the Japanese eel, and eel ovarian development corresponded to the decrease in ovarian PTEN expression, vice versa. In addition, the supplement of T on eel early ovarian development can be attributed to its PTEN inhibitor role.

Correlation Between PTEN and VEGF Expressions During the Development of Gas Gland in Japanese Eel (Anguilla japonica) Stimulated by Exogenous Hypophyseal Factors

Organogenesis requires support of the vascular system and control of proliferation activity. VEGF, a selective mitogen for vascular endothelial cells, is important for vessel development. PTEN, known as a tumor suppressor, regu- lates cell size and modulates VEGF-mediated signaling on angiogenesis. However, it is not yet clear if PTEN controls tis- sue mass by suppressing angiogenesis provoked by VEGF and their correlations in postnatal tissue development in vivo. We used a primitive vertebrate, Japanese eel (Anguilla japonica), to study this question. Swim bladder gas glands (a so- matic tissue composed mainly by the capillaries) from normal eels or eels injected with hypophyseal factors were used to examine the expression of VEGF A, PTEN, IGF-1, and Flk-1 by RT-PCR. Two forms of PTEN (PTEN a, long form, and PTEN b, short form) cDNA have been cloned. There was no correlation between VEGF expression and gas gland tissue mass while a negative correlation between PTEN expression and tissue mass was noted; further, a higher correlation be- tween the tissue mass and the ratio of VEGF to PTEN was shown. In summary, we have shown the involvement of VEGF and PTEN in postnatal tissue development, the ratio of VEGF to PTEN may represent the growth status of the tissue.

Lymphoid Microenvironment Inhibits Apoptosis in B-CLL Cells: Involvement of PI3-K/AKT Pathway and PTEN.

The activation of anti-apoptotic mechanisms in the leukemic B cells in chronic lymphocytic leukemia (B-CLL) through the interaction with their microenvironment may lead to prolonged survival and the accumulation of the malignant clone. The aim of this study is to elucidate the influence of the lymphoid microenvironment in the activation of the potent anti-apoptotic PI3-K/Akt pathway and to investigate the pattern of expression of the tumor suppressor PTEN in B-CLL. Stromal fibroblasts of bone marrow (BMF), spleen (SF) and lymph gland (LGF) were used as an in vitro model for lymphoid microenvironment. Pharmacological inhibitors and siRNAs against PI3-K and Akt were applied to explore the anti-apoptotic effect of this pathway in B-CLL. The results showed that co-cultivation of B-CLL cells with human BMF, LGF, and SF significantly inhibited apoptosis and prolonged survival of the leukemic cells in comparison to suspension cultures. To explore the involvement of PI3-K/Akt pathway in the anti-apoptotic effect of stromal fibroblasts, co-cultures were performed in presence of PI3-K inhibitors (wortmannin or LY294002) or siRNAs against PI3-K and Akt1. These inhibitors significantly reduced the supportive effect of stromal fibroblasts and induced apoptosis in B-CLL cells. The leukemic cells were more sensitive to PI3-K inhibition than T cells, monocytes and stromal fibroblasts. Induction of apoptosis was associated with a significant decrease in the intracellular levels of PIP3, PI3-K, PDK1, Akt1, NF-kappa B, IKK, and dephosphorylation (activation) of PTEN. Since PTEN activity, as a negative regulator for PI3-K signalling, is controlled by its phosphorylation at the tail domain, we studied the pattern of PTEN protein expression in B-CLL. Western blotting demonstrated that the total PTEN in PBMC of B-CLL patients (n=40) is comparable to healthy individuals (n=8). However, using phosphospecific anti-PTEN antibody demonstrated that samples of B-CLL patients highly express phosphorylated (inactive) forms of PTEN in comparison to healthy persons. In conclusion, the results demonstrate that PI3-K/Akt pathway is involved in inhibition of apoptosis of B-CLL cells and suggest that interaction of the leukemic cells with lymphoid microenvironment may lead to the activation of this pathway. The data also suggest that targeting this pathway represents a feasible therapeutic approach in B-CLL.

Tumor Suppressor Doing Double Duty

The tumor suppressor protein PTEN is a dual-specificity phosphatase whose catalytic domain acts primarily on lipids but can also target proteins. Raftopoulou et al. report that PTEN lipid phosphatase activity is not required for PTEN to inhibit cell migration. Instead, its protein phosphatase activity is required to dephosphorylate a single residue in its C-terminal tail, which in turn regulates migration. This mechanism may contribute to the progression of tumors that harbor catalytically inactive forms of PTEN. M. Raftopoulou, S. Etienne-Manneville, A. Self, S. Nicholls, A. Hall, Regulation of cell migration by the C2 domain of the tumor suppressor PTEN. Science 303 , 1179-1181 (2004). [Abstract] [Full Text]