Regulatory Factors of Cellular Senescence in Human Diploid Fibroblast : SA-p-Erk1/2, PP1/2A, PKCα

Proliferation of normal diploid cells is arrested irreversibly after a certain number of divisions, called replicative senescence, which is paragon of the general process of cellular senescence. Once senescent, cells continue to function metabolically, but will not respond to mitogens. Decreased growth rate, limited cell division, flat and large cell shapes, and increase of cell cycle regulator proteins are well-known characteristics of cells entered into senescence. Extracellular signal-regulated kinase 1/2 (Erk1/2) is one of the mitogenactivated protein kinase (MAPK). Erk1/2 signaling promotes cell proliferation and cell surnival. Ironically, p-Erk1/2 level is up-regulated in senescent cells. In the present study, the mechanism of senescence-associcated cytoplasmic induction of p-Erk1/2 (SA-p-Erk1/2) proteins in human diploid fibroblasts was investigated. Erk1/2 proteins were efficiently dephosphorylated in vitro by protein phosphatases 1 and 2A (PP1/2A). Specific activity of PP1/2A activity significantly decreased during cellular senescence, whereas their protein expression levels did not. SA-p-Erk1/2 was most likely due to the oxidation of PP1/2A, which resulted from continuous exposure of the cells to vast amounts of reactive oxygen species (ROS) generated during cellular senescence. Treatment of senescent human diploid fibroblast (HDF) cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), a well known protein kinase C (PKC) activator, induced morphological change and thymidine incorporation. PKC is a serine/threonine kinase and regulates signal transduction pathways involved in gene expression, cell proliferation, and differentiation. We also investigated activation and down-regulation of PKCa by TPA treatment, which reverses senescent HDF cells to young cell like shapes. Within 30min after TPA treatment, binding of PKCa and p- Erk1/2 was significantly increased, and both of them translocated to nucleus with progression of the cell cycle. When PKCa was down-regulated with siRNA treatment, the generation of ROS in mid-old cells was decreased accompanied with a typical change of the senescent HDF to young-cell like morphology. PKCa down-regulation induced the decrease of p53, p21^(WAF1), and SA-p-Erk1/2 in mid-old cells. In addition, PKCa down regulated midold cells regained its proliferation capacity. Therefore, these results suggest that PKCa works not only for maintenance of senescence phenotypes, but also for regulation of proliferation ability in cellular senescence.

Author dc:creator

• 김, 홍석

Contributors dc:contributor

• 임, 인경
• 대학원 의학과
• 103152

• Senescence
• SA-p-Erk1/2
• Protein phosphatase 1/2A
• TPA
• PKCα
• 세포 노화

Language dc:language

en

Identifier

http://dcoll.ajou.ac.kr:9080/dcollection/jsp/common/DcLoOrgPer.jsp?sItemId=000000006677
000000006677

OAI identifier oai:identifier

oai:repository.ajou.ac.kr:201003/1354