Stress-activated MAP kinase cascades in cellular senescence.

In response to progressive telomere shortening in successive cell divisions, normal somatic cells withdraw from the cell cycle and exhibit irreversible growth arrest. This state, called cellular senescence, is induced not only by telomere shortening but also by various physico-chemical stressors that induce DNA damage and chromatin disruption as well as by strong mitogenic signals. Because senescent cells never re-enter the cell cycle, cellular senescence appears to prevent malignant transformation of damaged cells and thus contributes to tumor suppression. On the other hand, excess accumulation of senescent cells attenuates the integrity and normal function of tissues, leading to age-related diseases. In addition to the well-established roles of p53 and pRB in cellular senescence, recent evidence suggests that stress-activated mitogen-activated protein kinase (MAPK) cascades that converge on c-Jun N-terminal kinases (JNKs) and p38 MAPKs also play important roles in the regulation of cellular senescence. In this review, we focus on signaling that regulates stress-induced cellular senescence, with special focus on the JNK and p38 MAPK cascades.