Downregulation of PEA-15 reverses G1 arrest, and nuclear and chromatin changes of senescence phenotype via pErk1/2 translocation to nuclei

Atorvastatin prevents hearing impairment in the presence of hyperlipidemia

It is known that hyperlipidemia is a risk factor for sensorineural hearing loss. However, the biological mechanisms underlying hyperlipidemia and hearing impairment have not been completely elucidated in the cochlea. Based on our previous study of human subjects, elderly people taking drugs for hyperlipidemia showed better hearing than those not taking any medications. We hypothesized that drugs for hyperlipidemia, such as statins, may have the potential to prevent hearing impairment. The aim of this study was to investigate the correlation between hyperlipidemia and hearing impairment and the hearing preservation effect of atorvastatin using a hyperlipidemic mouse model with diet-induced obesity (DIO). Here, we demonstrate that DIO mice had a significant hearing impairment as well as increased levels of reactive oxygen species (ROS) and hair cell death due to reduced levels of pAKT and superoxide dismutase 2 (SOD2). However, these changes were significantly prevented by atorvastatin. Oxidative stress-induced intrinsic apoptosis was decreased by the high expression of Nrf2 and antioxidant genes, which improved mitochondrial function and ROS via activation of the PI3K-pAKT pathway by atorvastatin. Therefore, atorvastatin has the potential to prevent hearing impairment via redox balance in the presence of hyperlipidemia.

Prognostic implication of proteomic profiles in head and neck squamous cell carcinoma

BACKGROUND AND OBJECTIVE

Head and neck squamous cell carcinoma (HNSCC) is one of the malignant cancers with poor prognosis. However, clinicopathologic and histological criteria were finite to predict the prognosis of HNSCC. We aimed to characterize the proteomic profile of prognosis from HNSCC patients.

MATERIAL AND METHODS

Reverse phase protein array (RPPA) data in HNSCC were downloaded from The Cancer Proteome Atlas (TCPA). Independent prognostic-related proteins (IPP) were screened by Cox regression model and Kaplan-Meier methods. IPP signature (IPPS) including selected proteins was conducted for prognostic prediction for HNSCC. Protein-protein network analysis and gene ontology (GO) enrichment were used to identify related functional proteins and pathways.

RESULTS

Based on the IPP, IPPS for HNSCC was constructed: risk score = (1.541* IRF1) + (1.460 * SMAD4) + (1.396 * LKB1) + (0.746* Cyclin E2) + (0.618* Paxillin) + (0.499* p-PEA-15 (Ser116)). The IPPS in HNSCC showed good predictive performance (area under curve = 0.779) with moderate sensitivity and specificity. Protein-protein network analysis and functional enrichment indicated an implication of response to decreased oxygen levels in HNSCC.

CONCLUSION

The identified proteomic signature might function as a prognostic tool for the management of HNSCC and provide novel target for the treatment of HNSCC.

Mitochondrial nucleoid remodeling and biogenesis are regulated by the p53-p21WAF1-PKCζ pathway in p16INK4a-silenced cells

Mitochondrial dysfunction is linked to age-related senescence phenotypes. We report here the pathway increasing nucleoid remodeling and biogenesis in mitochondria during the senescence of foreskin human diploid fibroblasts (fs-HDF) and WI-38 cells. Replicative senescence in fs-HDF cells increased mitochondrial nucleoid remodeling as indicated by 5-bromo-2'-deoxyuridine (BrdU) incorporation and mitochondrial transcription factor A (TFAM) expression in enlarged and fused mitochondria. Mitochondrial nucleoid remodeling was accompanied by mitochondrial biogenesis in old cells, and the expression levels of OXPHOS complex-I, -IV and -V subunits, PGC-1α and NRF1 were greatly increased compared to young cells. Activated protein kinase C zeta (PKCζ) increased mitochondrial activity and expressed phenotypes of delayed senescence in fs-HDF cells, but not in WI-38 cells. The findings were reproduced in the doxorubicin-induced senescence of young fs-HDF and WI-38 cells via the PKCζ-LKB1-AMPK signaling pathway, which was regulated by the p53-p21^WAF1 pathway when p16^INK4a was silenced. The signaling enhanced PGC-1α-NRF1-TFAM axis in mitochondria, which was demonstrated by Ingenuity Pathway Analysis of young and old fs-HDF cells. Activation of the p53-p21^WAF1 pathway and silencing of p16^INK4a are responsible for mitochondrial reprogramming in senescent cells, which may be a compensatory mechanism to promote cell survival under senescence stress.

High-fat diet unveils an enhancer element at the Ped/Pea-15 gene responsible for epigenetic memory in skeletal muscle

BACKGROUND

The impact of nutrition on the evolution towards type 2 diabetes has recently received increasing attention because of the effect on chromatin structure and gene expression.

PURPOSE

Evaluate the effect of high-fat diet on chromatin remodelling and expression of Ped/Pea-15, a gene commonly overexpressed in individuals at risk of type 2 diabetes.

METHODS

We used mouse and cell models to investigate Ped/Pea-15 transcriptional regulation by high-fat diet and glucose, respectively. Chromatin structure and histone modification marks were assessed by Micrococcal Nuclease Protection and Chromatin Immunoprecipitation assays.

RESULTS

Sixteen-week exposure of C57BL/6J mice to a high-fat diet impaired glucose tolerance and enhanced Ped/Pea-15 expression in their skeletal muscle tissue. This effect was associated with increased chromatin accessibility at specific regulatory sites at the Ped/Pea-15 gene. In particular, the region at -1900 to -1300 bp from Ped/Pea-15 transcription start site was revealed to feature enhancer activity as demonstrated by its function in the luciferase assay, increased p300 recruitment and H3K4me1 and H3K27Ac levels, all marks of functionally active enhancers. Returning mice to a standard chow diet was accompanied by rapid loss of acetylation of K27 on histone H3 and p300 recruitment at Ped/Pea-15. In contrast, the increased H3K4me1, which accompanied the high-fat diet exposure, remained stable. Incubation of muscle cells in culture medium supplemented with 25 mM glucose (HG) increased Ped/Pea-15 mRNA expression and H3K4me1 at the enhancer region. These effects became measurable upon 72 h of exposure to the HG medium and were not rescued upon returning the cells to the 5 mM glucose-containing medium. Interestingly, after 25 mM and sequential 5 mM glucose treatments, re-exposure of the same cells to HG medium further enhanced Ped/Pea-15 expression and increased H3K4me1 above the levels induced by the initial HG challenge already upon 24 h.

CONCLUSION

Transient exposure to HFD or HG unveiled the presence of an enhancer element at the Ped/Pea-15 gene. Epigenetic changes imposed at this region by diets, which impair glucose tolerance generate metabolic memory of the nutritional injury and leave Ped/Pea-15 induction in a poised state.

PEA-15 (Phosphoprotein Enriched in Astrocytes 15) Is a Protective Mediator in the Vasculature and Is Regulated During Neointimal Hyperplasia

BACKGROUND

Neointimal hyperplasia following angioplasty occurs via vascular smooth muscle cell proliferation. The mechanisms involved are not fully understood but include mitogen-activated protein kinases ERK1/2 (extracellular signal-regulated kinases 1 and 2). We recently identified the intracellular mediator PEA-15 (phosphoprotein enriched in astrocytes 15) in vascular smooth muscle cells as a regulator of ERK1/2-dependent proliferation in vitro. PEA-15 acts as a cytoplasmic anchor for ERK1/2, preventing nuclear localization and thereby reducing ERK1/2-dependent gene expression. The aim of the current study was to examine the role of PEA-15 in neointimal hyperplasia in vivo.

METHOD AND RESULTS

Mice deficient in PEA-15 or wild-type mice were subjected to wire injury of the carotid artery. In uninjured arteries from PEA-15-deficient mice, ERK1/2 had increased nuclear translocation and increased basal ERK1/2-dependent transcription. Following wire injury, arteries from PEA-15-deficient mice developed neointimal hyperplasia at an increased rate compared with wild-type mice. This occurred in parallel with an increase in a proliferative marker and vascular smooth muscle cell proliferation. In wild-type mice, PEA-15 expression was decreased in vascular smooth muscle cells at an early stage before any increase in intima:media ratio. This regulation of PEA-15 expression following injury was also observed in an ex vivo human model of hyperplasia.

CONCLUSIONS

These results indicate, for the first time, a novel protective role for PEA-15 against inappropriate vascular proliferation. PEA-15 expression may also be repressed during vascular injury, suggesting that maintenance of PEA-15 expression is a novel therapeutic target in vascular disease.

Shifting p53-induced senescence to cell death by TIS21(/BTG2/Pc3) gene through posttranslational modification of p53 protein

Cellular senescence and apoptosis can be regulated by p53 activity, although the underlying mechanism of the switch between the two events remains largely unknown. Cells exposed to cancer chemotherapy can escape to senescence phenotype rather than undergoing apoptosis. By employing adenoviral transduction of p53 or TIS21 genes, we observed shifting of p53 induced-senescence to apoptosis in EJ bladder cancer cells, which express H-RasV12 and mutant p53; transduction of p53 increased H-RasV12 expression along with senescence phenotypes, whereas coexpression with TIS21 (p53+TIS21) induced cell death rather than senescence. The TIS21-mediated switch of senescence to apoptosis was accompanied by nuclear translocation of p53 protein and its modifications on Ser-15 and Ser-46 phosphorylation and acetylations on Lys-120, -320, -373 and -382 residues. Mechanistically, TIS21(/BTG2) regulated posttranslational modification of p53 via enhancing miR34a and Bax expressions as opposed to inhibiting SIRT1 and Bcl2 expression. At the same time, TIS21 increased APAF-1 and p53AIP1 expressions, but inhibited the interaction of p53 with iASPP. In vitro tumorigenicity was significantly reduced in the p53+TIS21 expresser through inhibiting micro-colony proliferation by TIS21. Effect of TIS21 on the regulation of p53 activity was confirmed by knockdown of TIS21 expression by RNA interference. Therefore, we suggest TIS21 expression as an endogenous cell death inducer at the downstream of p53 gene, which might be useful for intractable cancer chemotherapy.

Regulations of Reversal of Senescence by PKC Isozymes in Response to 12-O-Tetradecanoylphorbol-13-Acetate via Nuclear Translocation of pErk1/2

The mechanism by which 12-O-tetradecanoylphorbol-13-acetate (TPA) bypasses cellular senescence was investigated using human diploid fibroblast (HDF) cell replicative senescence as a model. Upon TPA treatment, protein kinase C (PKC) α and PKCβ1 exerted differential effects on the nuclear translocation of cytoplasmic pErk1/2, a protein which maintains senescence. PKCα accompanied pErk1/2 to the nucleus after freeing it from PEA-15pS(104) via PKCβ1 and then was rapidly ubiquitinated and degraded within the nucleus. Mitogen-activated protein kinase docking motif and kinase activity of PKCα were both required for pErk1/2 transport to the nucleus. Repetitive exposure of mouse skin to TPA downregulated PKCα expression and increased epidermal and hair follicle cell proliferation. Thus, PKCα downregulation is accompanied by in vivo cell proliferation, as evidenced in 7, 12-dimethylbenz(a)anthracene (DMBA)-TPA-mediated carcinogenesis. The ability of TPA to reverse senescence was further demonstrated in old HDF cells using RNA-sequencing analyses in which TPA-induced nuclear PKCα degradation freed nuclear pErk1/2 to induce cell proliferation and facilitated the recovery of mitochondrial energy metabolism. Our data indicate that TPA-induced senescence reversal and carcinogenesis promotion share the same molecular pathway. Loss of PKCα expression following TPA treatment reduces pErk1/2-activated SP1 biding to the p21(WAF1) gene promoter, thus preventing senescence onset and overcoming G1/S cell cycle arrest in senescent cells.

On the Quest of Cellular Functions of PEA-15 and the Therapeutic Opportunities

Phosphoprotein enriched in astrocytes, 15 KDa (PEA-15), a ubiquitously expressed small protein in all mammals, is known for decades for its potent interactions with various protein partners along distinct biological pathways. Most notable interacting partners of PEA-15 include extracellular signal-regulated kinase 1 and 2 (ERK1/2) in the mitogen activated protein kinase (MAPK) pathway, the Fas-associated death domain (FADD) protein involving in the formation of the death-inducing signaling complex (DISC), and the phospholipase D1 (PLD1) affecting the insulin sensitivity. However, the actual cellular functions of PEA-15 are still mysterious, and the question why this protein is expressed in almost all cell and tissue types remains unanswered. Here we synthesize the most recent structural, biological, and clinical studies on PEA-15 with emphases on its anti-apoptotic, anti-proliferative, and anti-inflammative properties, and propose a converged protective role of PEA-15 that maintains the balance of death and survival in different cell types. Under conditions that this delicate balance is unsustainable, PEA-15 may become pathological and lead to various diseases, including cancers and diabetes. Targeting PEA-15 interactions, or the use of PEA-15 protein as therapeutics, may provide a wider window of opportunities to treat these diseases.