What is and What is Not Cell Senescence

Cell senescence is a process that occurs due to telomere erosion or can be induced by various stresses. Senescent cells cease to divide but remain alive, metabolically active and able to secrete many molecules. They also show many hallmarks of senescence, such as enlarged size, increased granularity, increased activity of SA-β-galactosidase, increased level of cyclin-dependent kinase inhibitors, p16 and p21, and DNA damage foci. Originally, cell senescence was attributed to proliferating normal cells, in contrast to cancer cells, which were considered as those endowed with indefinite growth ability. Recently, it has become evident that anticancer treatment induces senescence in cancer cells. Moreover, certain hallmarks of senescence were detected in non-proliferating post-mitotic cells. There are many signalling pathways involved in cell senescence, but the most prevalent is the DNA damage response pathway. In this review we have summarized our long lasting input in the global study of the mechanisms of senescence of normal and cancer cells and discussed the diversity of the concept of cell senescence.