Human papillomavirus 18 E6 inhibits phosphorylation of p53 expressed in HeLa cells

<p>Abstract</p> <p>Background</p> <p>In HPV infected cells p53 function is abrogated by E6 and even ectopically expressed p53 is unable to perform tumor suppressor functions. In addition to facilitating its degradation, E6 may also inhibit p53 transactivity, though the mechanisms are still poorly understood. It has been reported that inhibition of p300, an acetyltransferase responsible for p53 acetylation is inactivated by E6. Activation of overexpressed p53 to cause cell growth inhibition is facilitated by its phosphorylation. Previously, we reported that non-genotoxically overexpressed p53 in HeLa cells needs to be phosphorylated to perform its cell growth inhibitory functions. Since over expressed p53 by itself was not activated, we hypothesized an inhibitory role for E6.</p> <p>Results</p> <p>Majority of reports proposes E6 mediated degradation of p53 as a possible reason for its inactivation. However, results presented here for the first time demonstrate that overexpressed p53 is not directly associated with E6 and therefore free, yet it is not functionally active in HPV positive cells. Also, the stability of overexpressed p53 does not seem to be an issue because inhibition of proteasomal degradation did not increase the half-life of overexpressed p53, which is more than endogenous p53. However, inhibition of proteasomal degradation prevents the degradation of endogenous p53. These findings suggest that overexpressed p53 and endogenous p53 are differentially subjected to proteasomal degradation and the reasons for this discrepancy remain unclear. Our studies demonstrate that p53 over expression has no effect on anchorage independent cell-growth and E6 nullifies its cell growth inhibitory effect. E6 overexpression abrogates OA induced p53 occupancy on the p21 promoter and cell death as well. E6 did not decrease p53 protein but phospho-p53 level was significantly reduced.</p> <p>Conclusion</p> <p>We report for the first time that E6 de-activates p53 by inhibiting its phosphorylation. This prevents p53 binding to p21 promoter and thereby restraining its cell-growth inhibitory functions. Our study provides new evidence indicating that viral protein E6 inhibits p53 transactivity by mechanism independent of degradation pathway.</p

Heterozygosity for Fibrinogen Results in Efficient Resolution of Kidney Ischemia Reperfusion Injury

Fibrinogen (Fg) has been recognized to play a central role in coagulation, inflammation and tissue regeneration. Several studies have used Fg deficient mice (Fg−/−) in comparison with heterozygous mice (Fg+/−) to point the proinflammatory role of Fg in diverse pathological conditions and disease states. Although Fg+/− mice are considered ‘normal’, plasma Fg is reduced to ∼75% of the normal circulating levels present in wild type mice (Fg+/+). We report that this reduction in Fg protein production in the Fg+/− mice is enough to protect them from kidney ischemia reperfusion injury (IRI) as assessed by tubular injury, kidney dysfunction, necrosis, apoptosis and inflammatory immune cell infiltration. Mechanistically, we observed binding of Fg to ICAM-1 in kidney tissues of Fg+/+ mice at 24 h following IRI as compared to a complete absence of binding observed in the Fg+/− and Fg−/− mice. Raf-1 and ERK were highly activated as evident by significantly higher phosphorylation in the Fg+/+ kidneys at 24 h following IRI as compared to Fg+/− and Fg−/− mice kidneys. On the other hand Cyclin D1 and pRb, indicating higher cell proliferation, were significantly increased in the Fg+/− and Fg−/− as compared to Fg+/+ kidneys. These data suggest that Fg heterozygosity allows maintenance of a critical balance of Fg that enables regression of initial injury and promotes faster resolution of kidney damage

IL-34 mediates acute kidney injury and worsens subsequent chronic kidney disease

Macrophages (Mø) are integral in ischemia/reperfusion injury–incited (I/R-incited) acute kidney injury (AKI) that leads to fibrosis and chronic kidney disease (CKD). IL-34 and CSF-1 share a receptor (c-FMS), and both cytokines mediate Mø survival and proliferation but also have distinct features. CSF-1 is central to kidney repair and destruction. We tested the hypothesis that IL-34–dependent, Mø-mediated mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD. In renal I/R, the time-related magnitude of Mø-mediated AKI and subsequent CKD were markedly reduced in IL-34–deficient mice compared with controls. IL-34, c-FMS, and a second IL-34 receptor, protein-tyrosine phosphatase ζ (PTP-ζ) were upregulated in the kidney after I/R. IL-34 was generated by tubular epithelial cells (TECs) and promoted Mø-mediated TEC destruction during AKI that worsened subsequent CKD via 2 distinct mechanisms: enhanced intrarenal Mø proliferation and elevated BM myeloid cell proliferation, which increases circulating monocytes that are drawn into the kidney by chemokines. CSF-1 expression in TECs did not compensate for IL-34 deficiency. In patients, kidney transplants subject to I/R expressed IL-34, c-FMS, and PTP−ζ in TECs during AKI that increased with advancing injury. Moreover, IL-34 expression increased, along with more enduring ischemia in donor kidneys. In conclusion, IL-34-dependent, Mø-mediated, CSF-1 nonredundant mechanisms promote persistent ischemia-incited AKI that worsens subsequent CKD

Fat on sale: role of adipose-derived stem cells as anti-fibrosis agent in regenerative medicine

The potential use of stem cells for cell-based tissue repair and regeneration offers alternative therapeutic strategies for various diseases. Adipose-derived stem cells (ADSCs) have emerged as a promising source of stem cells suitable for transplantation in regenerative medicine and wound repair. A recent publication in Stem Cell Research & Therapy by Zhang and colleagues reports a new finding about the anti-fibrosis role of ADSCs and conditioned media derived from them on hypertrophic scar formation in vivo

Autophagy as a Therapeutic Target for Chronic Kidney Disease and the Roles of TGF-β1 in Autophagy and Kidney Fibrosis

Autophagy is a lysosomal protein degradation system that eliminates cytoplasmic components such as protein aggregates, damaged organelles, and even invading pathogens. Autophagy is an evolutionarily conserved homoeostatic strategy for cell survival in stressful conditions and has been linked to a variety of biological processes and disorders. It is vital for the homeostasis and survival of renal cells such as podocytes and tubular epithelial cells, as well as immune cells in the healthy kidney. Autophagy activation protects renal cells under stressed conditions, whereas autophagy deficiency increases the vulnerability of the kidney to injury, resulting in several aberrant processes that ultimately lead to renal failure. Renal fibrosis is a condition that, if chronic, will progress to end-stage kidney disease, which at this point is incurable. Chronic Kidney Disease (CKD) is linked to significant alterations in cell signaling such as the activation of the pleiotropic cytokine transforming growth factor-β1 (TGF-β1). While the expression of TGF-β1 can promote fibrogenesis, it can also activate autophagy, which suppresses renal tubulointerstitial fibrosis. Autophagy has a complex variety of impacts depending on the context, cell types, and pathological circumstances, and can be profibrotic or antifibrotic. Induction of autophagy in tubular cells, particularly in the proximal tubular epithelial cells (PTECs) protects cells against stresses such as proteinuria-induced apoptosis and ischemia-induced acute kidney injury (AKI), whereas the loss of autophagy in renal cells scores a significant increase in sensitivity to several renal diseases. In this review, we discuss new findings that emphasize the various functions of TGF-β1 in producing not just renal fibrosis but also the beneficial TGF-β1 signaling mechanisms in autophagy

Cdk5 phosphorylates non-genotoxically overexpressed p53 following inhibition of PP2A to induce cell cycle arrest/apoptosis and inhibits tumor progression

<p>Abstract</p> <p>Background</p> <p>p53 is the most studied tumor suppressor and its overexpression may or may not cause cell death depending upon the genetic background of the cells. p53 is degraded by human papillomavirus (HPV) E6 protein in cervical carcinoma. Several stress activated kinases are known to phosphorylate p53 and, among them cyclin dependent kinase 5 (Cdk5) is one of the kinase studied in neuronal cell system. Recently, the involvement of Cdk5 in phosphorylating p53 has been shown in certain cancer types. Phosphorylation at specific serine residues in p53 is essential for it to cause cell growth inhibition. Activation of p53 under non stress conditions is poorly understood. Therefore, the activation of p53 and detection of upstream kinases that phosphorylate non-genotoxically overexpressed p53 will be of therapeutic importance for cancer treatment.</p> <p>Results</p> <p>To determine the non-genotoxic effect of p53; Tet-On system was utilized and p53 inducible HPV-positive HeLa cells were developed. p53 overexpression in HPV-positive cells did not induce cell cycle arrest or apoptosis. However, we demonstrate that overexpressed p53 can be activated to upregulate p21 and Bax which causes G2 arrest and apoptosis, by inhibiting protein phosphatase 2A. Additionally, we report that the upstream kinase cyclin dependent kinase 5 interacts with p53 to phosphorylate it at Serine20 and Serine46 residues thereby promoting its recruitment on p21 and bax promoters. Upregulation and translocation of Bax causes apoptosis through intrinsic mitochondrial pathway. Interestingly, overexpressed activated p53 specifically inhibits cell-growth and causes regression <it>in vivo </it>tumor growth as well.</p> <p>Conclusion</p> <p>Present study details the mechanism of activation of p53 and puts forth the possibility of p53 gene therapy to work in HPV positive cervical carcinoma.</p

Multigenerational Effects of Graphene Oxide Nanoparticles on <i>Acheta domesticus</i> DNA Stability

The use of nanoparticles like graphene oxide (GO) in nanocomposite industries is growing very fast. There is a strong concern that GO can enter the environment and become nanopollutatnt. Environmental pollutants’ exposure usually relates to low concentrations but may last for a long time and impact following generations. Attention should be paid to the effects of nanoparticles, especially on the DNA stability passed on to the offspring. We investigated the multigenerational effects on two strains (wild and long-lived) of house cricket intoxicated with low GO concentrations over five generations, followed by one recovery generation. Our investigation focused on oxidative stress parameters, specifically AP sites (apurinic/apyrimidinic sites) and 8-OHdG (8-hydroxy-2′-deoxyguanosine), and examined the global DNA methylation pattern. Five intoxicated generations were able to overcome the oxidative stress, showing that relatively low doses of GO have a moderate effect on the house cricket (8-OHdG and AP sites). The last recovery generation that experienced a transition from contaminated to uncontaminated food presented greater DNA damage. The pattern of DNA methylation was comparable in every generation, suggesting that other epigenetic mechanisms might be involved