Tumor suppressor and aging biomarker p16(INK4a) induces cellular senescence without the associated inflammatory secretory phenotype

J Biol Chem. 2011 Oct 21;286(42):36396-403. doi: 10.1074/jbc.M111.257071. Epub 2011 Aug 31.

Abstract

Cellular senescence suppresses cancer by preventing the proliferation of cells that experience potentially oncogenic stimuli. Senescent cells often express p16(INK4a), a cyclin-dependent kinase inhibitor, tumor suppressor, and biomarker of aging, which renders the senescence growth arrest irreversible. Senescent cells also acquire a complex phenotype that includes the secretion of many cytokines, growth factors, and proteases, termed a senescence-associated secretory phenotype (SASP). The SASP is proposed to underlie age-related pathologies, including, ironically, late life cancer. Here, we show that ectopic expression of p16(INK4a) and another cyclin-dependent kinase inhibitor, p21(CIP1/WAF1), induces senescence without a SASP, even though they induced other features of senescence, including a stable growth arrest. Additionally, human fibroblasts induced to senesce by ionizing radiation or oncogenic RAS developed a SASP regardless of whether they expressed p16(INK4a). Cells induced to senesce by ectopic p16(INK4a) expression lacked paracrine activity on epithelial cells, consistent with the absence of a functional SASP. Nonetheless, expression of p16(INK4a) by cells undergoing replicative senescence limited the accumulation of DNA damage and premature cytokine secretion, suggesting an indirect role for p16(INK4a) in suppressing the SASP. These findings suggest that p16(INK4a)-positive cells may not always harbor a SASP in vivo and, furthermore, that the SASP is not a consequence of p16(INK4a) activation or senescence per se, but rather is a damage response that is separable from the growth arrest.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Cells, Cultured
  • Cellular Senescence / physiology*
  • Cellular Senescence / radiation effects
  • Coculture Techniques
  • Cyclin-Dependent Kinase Inhibitor p16 / genetics
  • Cyclin-Dependent Kinase Inhibitor p16 / metabolism*
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism
  • DNA Damage / drug effects
  • DNA Damage / physiology
  • Epithelial Cells / cytology
  • Epithelial Cells / metabolism*
  • Fibroblasts / cytology
  • Fibroblasts / metabolism*
  • Humans
  • Paracrine Communication / drug effects
  • Paracrine Communication / physiology*
  • Radiation, Ionizing

Substances

  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p16
  • Cyclin-Dependent Kinase Inhibitor p21