TP53 and infection: Infection of human vascular endothelial cells with a retroviral vector encoding sh-GPNMB caused depletion of GPNMB and shortened the replicative lifespan of these cells, along with an increase in the expression of p53 and p16Ink4a, as well as elevation of the activity of senescence-associated β-galactosidase (SA-β-gal) (Fig. 1a–c).