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Recently, we reported that cancer cells that recover from a potentially lethal damage gain new phenotypic features comprised of mitochondrial structural remodeling associated with increased glycolytic dependency and drug resistance. Here, we demonstrate that a subset of cancer cells, upon recovery from a potentially lethal damage, undergo dedifferentiation and express genes, which are characteristic of undifferentiated stem cells. While these cells are competent in maintaining differentiated progeny of tumor, they also exhibit transdifferentiation potential. Dedifferentiation is characterized by accumulation of hydrogen sulfide (H 2 S), which triggers up-regulation of nicotinamide phosphoribosyltransferase (Nampt) accompanied by changes in the redox state. The molecular events triggered by Nampt include elevated production of NAD + and up-regulation of H 2 S producing enzymes, cystathionine beta synthase (CBS) and cystathionase (CTH) with 3-mercaptopyruvate sulfurtransferase (MST) being detectable only in 3D spheroids. Suppression of Nampt, or inactivation of H 2 S producing enzymes, all reduce H 2 S production and reverse the ability of cells to dedifferentiate. Moreover, H 2 S induced stem cell markers in parental cancer cells in a manner similar to that observed in damage recovered cells. These data suggest of existence of a positive feedback loop between H 2 S and Nampt that controls dedifferentiation in cancer cells that recover from a potentially lethal damage. [ABSTRACT FROM AUTHOR]

Highlights: [•] Some cancer cells recover from severe damage that causes cell death in majority of cells. [•] Damage-Recovered (DR) cancer cells show reduced mitochondria, mDNA and mitochondrial enzymes. [•] DR cells show increased aerobic glycolysis, ATP, cell proliferation, and resistance to damage. [•] DR cells recovered from in vivo damage also show increased glycolysis and proliferation rate. [Copyright &y& Elsevier]

Abstract: The phosphoinositide 3′-kinase (PI3K)/Akt signaling cascade controls cellular processes such as apoptosis and proliferation. Moreover, it is a mediator of insulin effects on target cells and as such is a major regulator of fuel metabolism. The PI3K/Akt cascade was demonstrated to be activated by stressful stimuli, including heat shock and reactive oxygen species (ROS). This minireview focuses on activation of the pathway by exposure of cells to heavy metal ions, Cu2+ and Zn2+. It is hypothesized that stimulation of PI3K/Akt is the molecular mechanism underlying the known insulin-mimetic effects of copper and zinc ions. Following a brief summary of PI3K/Akt signaling and of activation of the cascade by Cu2+ and Zn2+, mechanisms of metal-induced PI3K/Akt activation are discussed with a focus on the role of ROS and of cellular thiols (glutathione, thioredoxin) and protein tyrosine phosphatases in Cu2+ and Zn2+ signaling. Finally, consequences of metal-induced PI3K/Akt activation are discussed, focusing on the modulation of FoxO-family transcription factors by Cu2+ and Zn2+. [Copyright &y& Elsevier]

Copper is implicated in metabolic disorders, such as Wilson''s disease or Alzheimer''s disease. Analysis of signaling pathways regulating cellular survival and function in response to a copper stress is crucial for understanding the pathogenesis of such diseases. Exposure of human skin fibroblasts or HeLa cells to Cu2+ resulted in a dose- and time-dependent activation of the antiapoptotic kinase Akt/protein kinase B, starting at concentrations as low as 3 μM. Only Cu(II), but not Cu(I), had this effect. Activation of Akt was accompanied by phosphorylation of a downstream target of Akt, glycogen synthase kinase-3. Inhibitors of phosphoinositide-3-kinase (PI3K) completely blocked activation of Akt by Cu2+, indicating a requirement of PI3K for Cu2+-induced activation of Akt. Indeed, cellular PI3K activity was strongly enhanced after exposure to Cu2+. Copper ions may lead to the formation of reactive oxygen species, such as hydrogen peroxide. Activation of Akt by hydrogen peroxide or growth factors is known to proceed via the activation growth factor receptors. In line with this, pretreatment with inhibitors of growth factor receptor tyrosine kinases blocked activation of Akt by hydrogen peroxide and growth factors, as did a src-family tyrosine kinase inhibitor or the broad-spectrum tyrosine kinase inhibitor genistein. Activation of Akt by Cu2+, however, remained unimpaired, implying (i) that tyrosine kinase activation is not involved in Cu2+ activation of Akt and (ii) that activation of the PI3K/Akt pathway by Cu2+ is initiated independently of that induced by reactive oxygen species. Comparison of the time course of the oxidation of 2′,7′-dichlorodihydrofluorescein in copper-treated cells with that of Akt activation led to the conclusion that production of hydroperoxides cannot be an upstream event in copper-induced Akt activation. Rather, both activation of Akt and generation of ROS are proposed to occur in parallel, regulating cell survival after a copper stress. [Copyright &y& Elsevier]

Transitioning from a differentiated state to a higher-order of plasticity, by partial rather than full reactivation of pluripotency genes, might be a better approach in regenerative medicine. Hydrogen sulfide plays a crucial role in the maintenance and differentiation of mesenchymal stem cells (MSC) that have the potential to differentiate to a diverse group of mesenchymally derived cells. It was shown that these cells show a heavy reliance on cystathionine-β-synthase (CBS)-derived hydrogen sulfide (H 2 S) during differentiation. We have found that expression and activity of 3-mercaptopyruvate sulfurtransferase (MPST), one of three enzymes that hat regulates H 2 S biosynthesis, is significantly lower in MSC as compared with lineage-restricted dermal fibroblasts. Here, we tested the hypothesis that suppression of MPST in dermal fibroblasts might induce plasticity-related changes and broaden the transdifferentiation potency. Inactivation of MPST with phenylpyruvate (PP) or by siRNA silencing led to diminished H 2 S production associated with increased production of reactive oxygen species (ROS) and lactic acid. Accumulation of α-ketoglutarate (α-KG), a key metabolite required for the expression of ten-eleven translocation hydroxylase (TET), was associated with stimulated transcription of pluripotency related genes including OCT4 , KLF4 , SOX2 , and NANOG. Suppression of TET1 gene and inhibition of glycolysis with glucose analog, 2-desoxy- d -glucose, or hexokinase II inhibitor significantly reduced expression of pluripotency genes following MPST inactivation or knockdown. MPST disruption promoted the conversion of fibroblasts into adipocytes as evidenced by a significant increase in expression of adipocyte-specific genes, PPARγ, and UCP1 , and intracellular accumulation of oil Red-O positive fat droplets. Inhibition of glycolysis inhibited these changes. Under induced differentiation conditions, fibroblasts with disrupted MPST show the potency to differentiate to white adipogenic lineage. Thus, MPST inactivation or silencing enhances the plasticity of dermal fibroblasts in a TET1 and glycolysis dependent manner and promotes adipogenic transdifferentiation. [ABSTRACT FROM AUTHOR]