PTEN Lipid Phosphatase Activity and Proper Subcellular Localization Are Necessary and Sufficient for Down-Regulating AKT Phosphorylation in the Nucleus in Cowden Syndrome
ABSTRACT Context:Germline mutations in PTEN are associated with phosphatase and tensin homolog deleted on chromosome 10 (PTEN) hamartoma tumor syndrome including Cowden syndrome (CS) and Cowden-like syndrome (CSL) that predisposes to high risks of benign and malignant tumors of thyroid and breast.Objective:The objective of the study was to analyze the subcellular pattern of phosphorylated (P)-AKT expression in nonmedullary thyroid cancers from PTEN hamartoma tumor syndrome patients and to investigate whether the lack of PTEN in the nucleus and/or lack of proper PTEN function in the nucleus affect(s) nuclear AKT activity in CS patients.Design:In all, 664 patients with CS/CSL were screened for PTEN germline mutations and nonmedullary thyroid cancers. Twenty-two patients who have both pathogenic PTEN germline mutations and nonmedullary thyroid cancers were selected. Thyroid samples from these patients were stained for PTEN and P-AKT. In our in vitro study, PTEN was knocked down or overexpressed in both thyroid cancer cells and breast cancer cells, and nuclear P-AKT was compared with the control.Results:Loss of PTEN protein was found in thyroid adenomas and carcinomas from all 22 (100%) PTEN(Mut+) CS/CSL patients. AKT activation was identified in 17 of 22 (77.3%) thyroid adenoma/carcinoma specimens, and most patients (63.7%) have activated nuclear AKT. Knockdown of PTEN in cells containing wild-type PTEN enhanced nuclear P-AKT, whereas expression of wild-type PTEN, but not phosphatase-dead mutants (C124S or G129E), markedly reduced nuclear P-AKT in PTEN null cells. We also showed that in breast cancer but not thyroid cancer cells, PTEN suppressesnuclear P-AKT mainly through decreasing P-AKT nuclear translocation by reducing the PIP3/P-AKT reservoir in the cytoplasm. In thyroid cancer cells, PTEN suppresses phosphorylation of AKT already resident in the nucleus.Conclusions:PTEN is necessary and sufficient for inhibiting AKT activation in the nucleus through its intact lipid phosphatase activity and proper subcellular localization.
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ABSTRACT: PTEN (Phosphatase and Tensin Homolog deleted on Chromosome TEN), the tumor suppressor is the regulator-in-chief of a variety of cellular processes that include cell proliferation, growth, migration and death. Since its identification, numerous reports of PTEN loss or mutation in multiple cancer types has rendered this gene to be one of the most frequently affected tumor suppressors of the post p53 era. With the ever increasing number of processes under PTEN surveillance, the master regulator itself should be under strict control. Although PTEN can be regulated at the genetic and epigenetic levels, post-translational modulations emerge as the focal point of regulation. Here, we will outline the key regulatory aspects of PTEN with an emphasis on the post-translational front. Exciting new evidences will be put forth for the sub-cellular trafficking of PTEN that regulates its functioning with a focus on ubiquitination, phosphorylation and sumoylation. The ability of PTEN to form protein scaffold structures has been overviewed from the aspect of novel regulatory mechanism. The probable contribution of these regulatory mechanisms in suppression or elevation of the tumor suppressive role of PTEN will be discussed. The role of the carboxyl terminus of PTEN in combating its negative regulators will be analyzed as a potential therapeutic approach. Overall, these under-rated, emerging modes of PTEN modulations significantly re-focus the established notion of PTEN regulation and might be targeted in unraveling novel cancer therapeutics.PTEN: Structure, Mechanisms-of-Action, Role in Cell Signaling and Regulation, Protein Science and Engineering; Protein Biochemistry, Synthesis, Structure and Cellular Functions edited by Ke Xu, 01/2013: chapter 2: pages 51-78; Nova Science Publishers., ISBN: 978-1-62808-049-0
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ABSTRACT: Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism to steer normal development and physiological functioning of multicellular organisms. Phosphotyrosine dephosphorylation is exerted by members of the super-family of protein tyrosine phosphatase (PTP) enzymes and many play such essential roles that a wide variety of hereditary disorders and disease susceptibilities in man are caused by PTP alleles. More than two decades of PTP research has resulted in a collection of PTP genetic variants with corresponding consequences at the molecular, cellular and physiological level. Here we present a comprehensive overview of these PTP gene variants that have been linked to disease states in man. Although the findings have direct bearing for disease diagnostics and for research on disease etiology, more work is necessary to translate this into therapies that alleviate the burden of these hereditary disorders and disease susceptibilities in man.Biochimica et Biophysica Acta 05/2013; 1832(10). DOI:10.1016/j.bbadis.2013.05.022 · 4.66 Impact Factor
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ABSTRACT: Context: TSH provokes expression of inflammatory genes in CD34(+) fibrocytes. These cells appear to infiltrate the orbit in Graves' disease (GD), where they putatively become the CD34(+) orbital fibroblast subset (GD-OF). This may have importance in solving the pathogenesis of thyroid-associated ophthalmopathy (TAO). The interleukin-1 (IL-1) family is targeted by TSH in fibrocytes and OF by inducing secreted IL-1 receptor antagonist (sIL-1RA) and intracellular (icIL-1RA) in a cell-specific pattern. Phosphoinositide 3-kinase (PI3K) mediates several TSH actions in thyroid. This pathway is modulated by phosphatase and tensin homolog deleted on chromosome ten (PTEN). Vanishingly little is known currently about TSHR signaling to IL-1RA expression in non-thyroidal cells. Further, factors modulating TSH action in these cells are largely unexplored. Objective: To characterize intermediate signaling between TSHR and IL-1RA in fibrocytes and GD-OF. To begin to identify the proximate regulators of TSHR signaling in non-epithelial, extra-thyroidal cells as a strategy for developing therapies for TAO. Design/Setting/Participants: Fibrocytes and GD-OF were collected and analyzed from healthy individuals and those with GD in an academic clinical practice. Main outcome measures: Real-time PCR, Western blot analysis, cell transfections, CHIP analysis. Results: TSH induces IL-1RA in fibrocytes and GD-OF by activating the PI3K/AKT pathway. Interrupting either PI3K or AKT with small molecule inhibitors or by knocking down their expression with targeting siRNA attenuates the actions of TSH. OF exhibit greater basal PTEN activity and lower constitutive AKT phosphorylation than do fibrocytes. Patterns of PTEN induction diverge in the two cell types. Conclusions: The current findings identify PI3K/AKT pathway as critical to the induction by TSH of IL-1RA in fibrocytes and GD-OF. Further PTEN modulates the amplitude of the induction. In GD-OF, relatively high basal PTEN levels prevent sIL-1RA expression or release of IL-1RA. Knocking down PTEN allows GD-OF to exhibit a pattern of IL-1RA expression resembling fibrocytes.Journal of Clinical Endocrinology & Metabolism 05/2014; 99(9):jc20141257. DOI:10.1210/jc.2014-1257 · 6.31 Impact Factor