Gene expression levels and kinetics of endocytosis in senescing cells.

<p>(A) mRNA levels of ITSN2, EPS15, HSP70, and JAK2 were compared in young and old fibroblasts. Levels were normalized to GAPDH. Levels of p16 and ING1a mRNA serve as controls to confirm the senescent state of cells. (B) EGFR degradation was examined in low passage and senescing cells. The samples were prepared as described previously, and EGFR amounts were estimated by western blotting. EGFR persisted in senescent compared to young cells, and ING1a was expressed at much higher levels in senescent cells as previously reported <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001502#pbio.1001502-Soliman1" target="_blank">[23]</a>. (C) mRNA levels of ITSN2 and other endocytic genes in cells knocked down for ING1a using siRNA (<i>p</i><0.05). (D) ING1a and ITSN2 levels in other forms of stress induced premature senescence (SIPS) using doxorubicin and t-butyl hydroperoxide. P16 and p21 are cyclin-dependent kinase inhibitors that serve as senescence markers, and HSP70 as a stress marker. The top panels show SA-β-gal staining as a marker for senescence induction in response to the treatments noted.