Diperoxovanadate can substitute for H(2)O(2) at much lower concentration in inducing features of premature cellular senescence in mouse fibroblasts (NIH3T3)

Stress induced premature senescence (SIPS) in mammalian cells is an accelerated ageing response and experimentally obtained on treatment of cells with high concentrations of H(2)O(2), albeit at sub-lethal doses, because H(2)O(2) gets depleted by abundant cellular catalase. In the present study diperoxovanadate (DPV) was used as it is known to be stable at physiological pH, to be catalase-resistant and to substitute for H(2)O(2) in its activities at concentrations order of magnitudes lower. On treating NIH3T3 cells with DPV, SIPS-like morphology was observed along with an immediate response of rounding of the cells by disruption of actin cytoskeleton and transient G2/M arrest. DPV could bring about growth arrest and senescence associated features at 25 mu M dose, which were not seen with similar doses of either H(2)O(2) or vanadate. A minimal dose of 150 mu M of H(2)O(2) was required to induce similar affects as 25 mu M DPV. Increase in senescent associated markers such as p21, HMGA2 and PAI-1 was more prominent in DPV treated cells compared to similar dose of H(2)O(2). DPV-treated cells showed marked relocalization of Cyclin D1 from nucleus to cytoplasm. These results indicate that DPV, stable inorganic peroxide, is more efficient in inducing SIPS at lower concentrations compared to H(2)O(2). (C) 2011 Elsevier Ireland Ltd. All rights reserved

Heat shock factor 1 (HSF1) specifically potentiates c-MYC-mediated transcription independently of the canonical heat shock response

Summary: Despite its pivotal roles in biology, how the transcriptional activity of c-MYC is tuned quantitatively remains poorly defined. Here, we show that heat shock factor 1 (HSF1), the master transcriptional regulator of the heat shock response, acts as a prime modifier of the c-MYC-mediated transcription. HSF1 deficiency diminishes c-MYC DNA binding and dampens its transcriptional activity genome wide. Mechanistically, c-MYC, MAX, and HSF1 assemble into a transcription factor complex on genomic DNAs, and surprisingly, the DNA binding of HSF1 is dispensable. Instead, HSF1 physically recruits the histone acetyltransferase general control nonderepressible 5 (GCN5), promoting histone acetylation and augmenting c-MYC transcriptional activity. Thus, we find that HSF1 specifically potentiates the c-MYC-mediated transcription, discrete from its canonical role in countering proteotoxic stress. Importantly, this mechanism of action engenders two distinct c-MYC activation states, primary and advanced, which may be important to accommodate diverse physiological and pathological conditions

Peroxo Compounds of Vanadium(V) and Niobium(V) as Potent Inhibitors of Calcineurin Activity towards RII-Phosphopeptide

Calcineurin (CN) is a major calmodulin binding serine/threonine phosphatase which plays a crucial role in numerous mammalian signal transduction pathways. Calcineurin inhibitors represent a valuable tool for elucidating CN dependent cellular processes. The present work deals with the synthesis and comprehensive characterization of a new polymer anchored peroxo niobium complex, Nb-2(O-2)(6)(carboxylate)(2)]-PA (Nb-2) PA=poly(sodium acrylate)], and identification of a set comprising of neat homoleptic as well as polymer immobilized peroxo complexes of vanadium(V) and niobium(V) as potent CN inhibitors. The in-vitro effect of the complexes on calmodulin mediated dephosphorylation activity of CN was investigated using a physiological substrate of calcineurin, RII-phosphopeptide as well as a non-protein substrate p-nitrophenyl phosphate (p-NPP). Enzyme kinetic analysis data revealed that the compounds inhibit function of CN via uncompetitive pathway with K-i values ranging between 1-3M, suggesting the formation of an enzyme-inhibitor-substrate complex during the course of inhibition