1432

MAPK14

mitogen-activated protein kinase 14;MAPK14;mitogen-activated protein kinase 14

CSAID-binding protein|Csaids binding protein|MAP kinase 14|MAP kinase Mxi2|MAP kinase p38 alpha|MAX-interacting protein 2|cytokine suppressive anti-inflammatory drug binding protein|cytokine suppressive anti-inflammatory drug-binding protein|mitogen-activ

6p21.3-p21.2

protein-coding

BACKGROUND: Both the number and function of bone marrow-derived endothelial progenitor cells (EPCs) have been shown to be impaired in patients with diabetes mellitus. Therefore, we investigated the effect of glucose on the senescence of EPCs. METHODS AND RESULTS: EPCs were isolated from human peripheral blood and characterized to evaluate the effect of glucose (in 5-12.5 mmol/L) on the rate of senescence by acidic beta-galactosidase staining. The phosphorylation of p38 mitogen-activated protein kinase (MAPK) level was analyzed by ELISA. The exposure of cultured EPC to high glucose (HG; 12.5 mmol/L) significantly accelerated the rate of senescence compared with that in osmolar control (L-glucose) during 10 days culture. An inhibitory effect of HG on EPC proliferation disclosed by an MTS assay. The phosphorylation of p38 MAPK in EPCs was also increased by glucose compared with control in a dose-dependent manner. HG-induced EPC senescence was significantly inhibited by the addition of an inhibitor of the p38 MAPK, SB203580. CONCLUSIONS: HG accelerates the onset of EPCs senescence leading to the impairment of proliferative activity, which might be related to the phosphorylation of p38 MAPK.

We previously reported that tumor cells expressing p53 increase intracellular levels of reactive oxygen species (ROS). In this study, we described an inhibitory effect of vitamin C on replicative senescence. Vitamin C was found to inhibit p53-induced senescence in human bladder cancer EJ cells. The senescence-like phenotype (SLP) induced by p53, which showed a morphological change and an irreversible cell cycle arrest, was not observed in vitamin C-treated EJ cells. In addition, vitamin C did not significantly affect normal cell proliferation. We investigated the molecular mechanisms of the inhibitory effect of vitamin C on the development of replicative senescence in EJ cells. We found that vitamin C inhibited this p53-induced ROS generation. Moreover, p38 kinase which was activated during p53-induced senescence was not observed in vitamin C-treated EJ cells. SB203580, a chemical inhibitor of p38 kinase, was found to consistently inhibit p53-induced senescence. Therefore, it is suggested that vitamin C inhibits p53-induced senescence by preventing ROS generation, which in turn leads to the activation of p38 MAPKinase. These results reveal the inhibitory mechanism of vitamin C on cellular senescence.

Radiotherapy is increasingly used in the treatment of joint diseases, but limited information is available on the effects of radiation on cartilage. Here, we characterize the molecular mechanisms leading to cellular senescence in irradiated primary cultured articular chondrocytes. Ionizing radiation (IR) causes activation of ERK, in turn generating intracellular reactive oxygen species (ROS) with induction of senescence-associated beta-galactosidase (SA-beta-gal) activity. ROS activate p38 kinase, which further promotes ROS generation, forming a positive feedback loop to sustain ROS-p38 kinase signaling. The ROS inhibitors, nordihydroguaiaretic acid and GSH, suppress phosphorylation of p38 and cell numbers positive for SA-beta-gal following irradiation. Moreover, inhibition of the ERK and p38 kinase pathways leads to blockage of IR-induced SA-beta-gal activity via reduction of ROS generation. Although JNK is activated by ROS, this pathway is not associated with cellular senescence of chondrocytes. Interestingly, IR triggers down-regulation of SIRT1 protein expression but not the transcript level, indicative of post-transcriptional cleavage of the protein. SIRT1 degradation is markedly blocked by SB203589 or MG132 after IR treatment, suggesting that cleavage occurs as a result of binding with p38 kinase, followed by processing via the 26 S proteasomal degradation pathway. Overexpression or activation of SIRT1 significantly reduces the IR-induced senescence phenotype, whereas inhibition of SIRT1 activity induces senescence. Based on these findings, we propose that IR induces cellular senescence of articular chondrocytes by negative post-translational regulation of SIRT1 via ROS-dependent p38 kinase activation.

Patients treated with low-dose anthracyclines often show late onset cardiotoxicity. Recent studies suggest that this form of cardiotoxicity is the result of a progenitor cell disease. In this study we demonstrate that Cord Blood Endothelial Progenitor cells (EPCs) exposed to low, sub-apoptotic doses of doxorubicin show a senescence phenotype characterized by increased SA-b-gal activity, decreased TRF2 and chromosomal abnormalities, enlarged cell shape, and disarrangement of F-actin stress fibers accompanied by impaired migratory ability. P16( INK4A) localizes in the cytoplasm of doxorubicin-induced senescent EPCs and not in the nucleus as is the case in EPCs rendered senescent by different stimuli. This localization together with the presence of an arrest in G2, and not at the G1 phase boundary, which is what usually occurs in response to the cell cycle regulatory activity of p16(INK4A), suggests that doxorubicin-induced p16( INK4A) does not regulate the cell cycle, even though its increase is closely associated with senescence. The effects of doxorubicin are the result of the activation of MAPKs p38 and JNK which act antagonistically. JNK attenuates the senescence, p16( INK4A) expression and cytoskeleton remodeling that are induced by activated p38. We also found that conditioned medium from doxorubicin-induced senescent cardiomyocytes does not attract untreated EPCs, unlike conditioned medium from apoptotic cardiomyocytes which has a strong chemoattractant capacity. In conclusion, this study provides a better understanding of the senescence of doxorubicin-treated EPCs, which may be helpful in preventing and treating late onset cardiotoxicity.

DNA-damaging agents are able to induce irreversible cell growth arrest and senescence in some types of tumour cells, thus contributing to the static feature of cancer. However, senescent tumour cells may re-enter the cell cycle, leading to tumour relapse. Understanding the mechanisms that control the viability of senescent cells may be critical for tumour suppression. Primary human fibroblasts undergoing oncogene-induced or replicative senescence are known to form senescence-associated heterochromatin foci (SAHF), which contribute to the stability of the senescent state. However, it is unclear whether SAHF formation is universal in tumour cells. We report that the DNA-damaging agents doxorubicin and 7-ethyl-10-hydroxycamptothecin were able to induce the formation of SAHF in some tumour cell types, and this induction was accompanied by activation of the retinoblastoma protein pathway. By contrast, tumour cells in which the retinoblastoma protein pathway could not be activated by doxorubicin or 7-ethyl-10-hydroxycamptothecin failed to form SAHF. In parallel, tumour cells with deficient retinoblastoma protein were also unable to form SAHF. In addition, we show that the mitogen-activated protein kinase p38 pathway was involved in tumour cell SAHF formation in response to doxorubicin and 7-ethyl-10-hydroxycamptothecin. Furthermore, HMG box transcription factor 1 (HBP1), a downstream target of the mitogen-activated protein kinase p38-mediated senescence pathway, was required for SAHF formation. Taken together, the results of the present study highlight the roles of the mitogen-activated protein kinase p38/retinoblastoma protein pathway in tumour cell SAHF formation in response to DNA-damaging agents, and provide new insights into the mechanisms of DNA damage-mediated tumour suppression.

Mammalian cells may undergo permanent growth arrest/senescence when they incur excessive DNA damage. As a key player during DNA damage response (DDR), p53 transactivates an array of target genes that are involved in various cellular processes including the induction of cellular senescence. Chemokine receptor CXCR2 was previously reported to mediate replicative and oncogene-induced senescence in a DDR and p53-dependent manner. Here, we report that CXCR2 is upregulated in various types of cells in response to genotoxic or oxidative stress. Unexpectedly, we found that the upregulation of CXCR2 depends on the function of p53. Like other p53 target genes such as p21, CXCR2 is transactivated by p53. We identified a p53-binding site in the CXCR2 promoter that responds to changes in p53 functional status. Thus, CXCR2 may act downstream of p53. While the senescence-associated secretory phenotype (SASP) exhibits a kinetics that is distinct from that of CXCR2 expression and does not require p53, it reinforces senescence. We further showed that the cellular senescence caused by CXCR2 upregulation is mediated by p38 activation. Our results thus demonstrate CXCR2 as a critical mediator of cellular senescence downstream of p53 in response to DNA damage.

Interleukin (IL)-4, originally identified as a lymphocyte growth factor, can directly inhibit growth of certain tumor cell types. We reported previously that IL-4 induced cell cycle arrest in G1 phase through an increase in p21(WAF1/CIP1) expression in human renal cell carcinoma (RCC) cell lines. In the present study, we investigated the underlying mechanism of IL-4-induced growth inhibition. In four of six human RCC cell lines, including Caki-1, A498, SNU482, and SNU228, IL-4 induced cellular senescence as demonstrated by enlarged and flattened morphology, increased granularity, and senescence-associated-beta-galactosidase (SA-beta-gal) staining. Signal tranducer and activator of transcription 6 (STAT6) and p38 MAPK were found to mediate IL-4-induced growth inhibition and cellular senescence. Both of these molecules were activated by 10 min after IL-4 treatment, and inhibition of their activity or expression prevented growth suppression and cellular senescence induced by IL-4. Inhibiting or silencing either STAT6 or p38 MAPK alone partially reduced the effect of IL-4, whereas inhibiting or silencing both molecules exerted an additive effect and almost completely abrogated the effect of IL-4. Thus STAT6 and p38 MAPK appeared to independently mediate IL-4-induced growth inhibition and cellular senescence. The p21(WAF1/CIP1) up-regulation that accompanied growth inhibition and cellular senescence by IL-4 was also attenuated additively when p38 MAPK and STAT6 were silenced. Taken together, these results show that IL-4 induces cellular senescence through independent signaling pathways involving STAT6 and p38 MAPK in some human RCC cell lines.