Perp loss compromises UVB-induced apoptosis <i>in vivo</i> and <i>in vitro</i>.

<p>A) Perp immunohistochemistry showing loss of Perp in the epidermis of tamoxifen-treated <i>K14CreER;Perp^fl/fl</i> mice. Dashed line demarcates epidermis (EP) and dermis (D). B) Immunohistochemistry showing p53 stabilization (arrows) in the epidermis of both control and <i>K14CreER;Perp^fl/fl</i> mice 24 hrs after treatment with 2.5 kJ/m² UVB radiation. C) Cleaved Caspase 3 (CC3) immunohistochemistry to detect apoptosis in the epidermis of untreated and UVB-treated mice of different genotypes. Arrows indicate apoptotic cells. D) Quantification of apoptosis in untreated and UVB-treated control, <i>K14CreER;Perp^fl/fl</i>, and <i>p53−/−</i> mice. Graph depicts the average number of cleaved Caspase 3 (CC3)- positive cells per linear cm of epidermis, +/− SEM. Data were derived from the analysis of segments of skin at least 2–3 cm long per mouse, in several independent experiments with the following numbers of mice: wild-type controls (n = 8), <i>K14CreER;Perp^fl/fl</i> (n = 12), <i>p53−/−</i> (n = 5). Statistical analysis was conducted using the Student's unpaired t-test (* p = 0.0017 versus treated wild-type and ** p = 0.0003 versus treated wild-type). (E) Representative immunofluorescence images of wild-type, <i>Perp−/−</i>, and <i>p53−/−</i> keratinocyte monolayers, either untreated or treated with 1 kJ/m² UVB, and stained with a cleaved Caspase 3 antibody and DAPI to measure apoptosis. (F) Higher magnification images show apoptotic cells, which display both cleaved Caspase 3-positivity and nuclear blebbing and chromatin condensation by DAPI staining, hallmarks of apoptosis (G) Quantitation of the percentage of apoptotic cells per 200× field in untreated and UVB-treated wild-type, <i>Perp−/−</i>, and <i>p53−/−</i> keratinocytes, as assessed by cleaved Caspase 3/DAPI staining. Graph represents the average +/− SEM of three independent experiments performed in triplicate. Statistical analysis was conducted using the Student's unpaired t-test. (* p = 0.011 versus treated wild-type and ** p = 0.0029 versus treated wild-type).