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Mandal C.C.,University of Texas Health Science Center at San Antonio | Ganapathy S.,University of Texas Health Science Center at San Antonio | Gorin Y.,University of Texas Health Science Center at San Antonio | Mahadev K.,University of Pennsylvania | And 7 more authors.
Biochemical Journal | Year: 2011

BMP-2 (bone morphogenetic protein-2) promotes differentiation of osteoblast precursor cells to mature osteoblasts that form healthy bone. In the present study, we demonstrate a novel mechanism of BMP-2-induced osteoblast differentiation. The antioxidant NAC (N-acetyl-L-cysteine) and the flavoprotein enzyme NAD(P)H oxidase inhibitor DPI (diphenyleneiodonium) prevented BMP-2-stimulated alkaline phosphatase expression and mineralized bone nodule formation in mouse 2T3 pre-osteoblasts. BMP-2 elicited a rapid generation of ROS (reactive oxygen species) concomitant with increased activation of NAD(P)H oxidase. NAC andDPI inhibited BMP-2-induced ROS production and NAD(P)H oxidase activity respectively. NAD(P)H oxidases display structurally similar catalytic subunits (Nox1-5) with differential expression in various cells. We demonstrate that 2T3 pre-osteoblasts predominantly express the Nox4 isotype of NAD(P)H oxidase. To extend this finding, we tested the functional effects of Nox4. Adenovirus-mediated expression of dominant-negative Nox4 inhibited BMP-2-induced alkaline phosphatase expression. BMP-2 promotes expression of BMP-2 for maintenance of the osteoblast phenotype. NAC and DPI significantly blocked BMP-2-stimulated expression of BMP2 mRNA and protein due to a decrease in BMP2 gene transcription. Dominant-negative Nox4 also mimicked this effect of NAC and DPI. Our results provide the first evidence for a new signalling pathway linking BMP-2-stimulated Nox4-derived physiological ROS to BMP-2 expression and osteoblast differentiation. © The Authors Journal compilation © 2011 Biochemical Society. Source

Mandal C.C.,University of Texas Health Science Center at San Antonio | Drissi H.,University of Connecticut Health Center | Ghosh Choudhury G.,University of Texas Health Science Center at San Antonio | Ghosh Choudhury G.,Geriatric Research | And 3 more authors.
Calcified Tissue International | Year: 2010

Osterix (Osx), a BMP-2-regulated transcription factor, controls expression of genes essential for osteoblast differentiation. Using progressive deletion of the Osx promoter, we characterized a Smad binding element (SBE) between -552 and -839 bp from its transcription start site. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay showed binding and in vivo recruitment of Smads 1 and 5 to the Osx SBE. Inactivation of PI 3-kinase by the pharmacologic inhibitor Ly294002 or by dominant negative (DN) enzyme significantly blocked BMP-2-induced Osx protein and mRNA expression and Osx transcription. Finally, both DN PI 3-kinase and DN Akt significantly attenuated Smad 5-dependent transcription of Osx, demonstrating the first evidence for a concerted action of PI 3-kinase/Akt signaling with BMP-specific Smads for expression of Osx. © 2010 Springer Science+Business Media, LLC. Source

Das F.,University of Texas Health Science Center at San Antonio | Dey N.,University of Texas Health Science Center at San Antonio | Venkatesan B.,University of Texas Health Science Center at San Antonio | Kasinath B.S.,University of Texas Health Science Center at San Antonio | And 6 more authors.
Cellular Signalling | Year: 2011

The Akt kinase signaling pathway is frequently deregulated in many human diseases including cancer, autoimmune disease and diabetes. In nephropathy, associated with diabetes, increased Akt signal transduction results in glomerular especially mesangial cell hypertrophy. The mechanism of Akt activation by elevated glucose is poorly understood. The oncogene DJ-1 prevents oxidative damage and apoptosis of dopaminergic neurons in animal models of Parkinson's disease and in culture. We identified DJ-1 to increase in response to high glucose in renal glomerular mesangial cells concomitant with an increase in phosphorylation of Akt in a time-dependent manner. Plasmid-derived overexpression as well as downregulation of DJ-1 by siRNA showed the requirement of this protein in high glucose-stimulated Akt phosphorylation. The tumor suppressor protein PTEN acts as a negative regulator of Akt activation. Interestingly, DJ-1 was associated with PTEN and this interaction was significantly increased in response to high glucose. High glucose-induced increase in DJ-1 promoted phosphorylation of the PRAS40, a negative regulator of TORC1 kinase activity, resulting in activating and inactivating phosphorylation of S6 kinase and 4EBP-1, respectively. Furthermore, DJ-1 increased protein synthesis and hypertrophy of mesangial cells. Our results provide evidence for a unique mechanism whereby DJ-1 induces Akt/PRAS40/TORC1-mediated hypertrophy in response to high glucose. © 2011 Elsevier Inc. Source

Das F.,University of Texas Health Science Center at San Antonio | Ghosh-Choudhury N.,University of Texas Health Science Center at San Antonio | Ghosh-Choudhury N.,VA Research | Bera A.,University of Texas Health Science Center at San Antonio | And 5 more authors.
Journal of Cellular Physiology | Year: 2013

Transforming growth factorβ (TGFβ)-induced canonical signal transduction is involved in glomerular mesangial cell hypertrophy; however, the role played by the noncanonical TGFβ signaling remains largely unexplored. TGFβ time-dependently stimulated eIF4E phosphorylation at Ser-209 concomitant with enhanced phosphorylation of Erk1/2 (extracellular signal regulated kinase1/2) and MEK (mitogen-activated and extracellular signal-regulated kinase kinase) in mesangial cells. Inhibition of Erk1/2 by MEK inhibitor or by expression of dominant negative Erk2 blocked eIF4E phosphorylation, resulting in attenuation of TGFβ-induced protein synthesis and mesangial cell hypertrophy. Expression of constitutively active (CA) MEK was sufficient to induce protein synthesis and hypertrophy similar to those induced by TGFβ. Pharmacological or dominant negative inhibition of phosphatidylinositol (PI) 3 kinase decreased MEK/Erk1/2 phosphorylation leading to suppression of eIF4E phosphorylation. Inducible phosphorylation of eIF4E at Ser-209 is mediated by Mnk-1 (mitogen-activated protein kinase signal-integrating kinase-1). Both PI 3 kinase and Erk1/2 promoted phosphorylation of Mnk-1 in response to TGFβ. Dominant negative Mnk-1 significantly inhibited TGFβ-stimulated protein synthesis and hypertrophy. Interestingly, inhibition of mTORC1 activity, which blocks dissociation of eIF4E-4EBP-1 complex, decreased TGFβ-stimulated phosphorylation of eIF4E without any effect on Mnk-1 phosphorylation. Furthermore, mutant eIF4E S209D, which mimics phosphorylated eIF4E, promoted protein synthesis and hypertrophy similar to TGFβ. These results were confirmed using phosphorylation deficient mutant of eIF4E. Together our results highlight a significant role of dissociation of 4EBP-1-eIF4E complex for Mnk-1-mediated phosphorylation of eIF4E. Moreover, we conclude that TGFβ-induced noncanonical signaling circuit involving PI 3 kinase-dependent Mnk-1-mediated phosphorylation of eIF4E at Ser-209 is required to facilitate mesangial cell hypertrophy. J. Cell. © 2013 Wiley Periodicals, Inc. Source

Ghosh-Choudhury N.,University of Texas Health Science Center at San Antonio | Mandal C.C.,University of Texas Health Science Center at San Antonio | Ghosh-Choudhury N.,VA Research | Ghosh Choudhury G.,VA Research | And 2 more authors.
Cellular Signalling | Year: 2010

Sustained activation of Akt kinase acts as a focal regulator to increase cell growth and survival, which causes tumorigenesis including breast cancer. Statins, potent inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, display anticancer activity. The molecular mechanisms by which statins block cancer cell growth are poorly understood. We demonstrate that in the tumors derived from MDA-MB-231 human breast cancer cell xenografts, simvastatin significantly inhibited phosphorylation of Akt with concomitant attenuation of the expression of the anti-apoptotic protein Bcl XL. In many cancer cells, Bcl XL is a target of NFκB. Simvastatin inhibited the DNA binding and transcriptional activities of NFκB resulting in marked reduction in transcription of Bcl XL. Signals transmitted by anti-neoplastic mechanism implanted in the cancer cells serve to obstruct the initial outgrowth of tumors. One such mechanism represents the action of the tumor suppressor protein PTEN, which negatively regulates Akt kinase activity. We provide the first evidence for significantly increased levels of PTEN in the tumors of simvastatin-administered mice. Importantly, simvastatin markedly prevented binding of NFκB to the two canonical recognition elements, NFRE-1 and NFRE-2 present in the PTEN promoter. Contrary to the transcriptional suppression of Bcl XL, simvastatin significantly increased the transcription of PTEN. Furthermore, expression of NFκB p65 subunit inhibited transcription of PTEN, resulting in reduced protein expression, which leads to enhanced phosphorylation of Akt. Taken together, our data present a novel bifaceted mechanism where simvastatin acts on a nodal transcription factor NFκB, which attenuates the expression of anti-apoptotic Bcl XL and simultaneously derepresses the expression of anti-proliferative/proapoptotic tumor suppressor PTEN to prevent breast cancer cell growth. © 2010. Source

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