PKCdelta in Insulin Secreting Cells Figure 6. Cells treated with siRNA against PKCd accumulate dephosphorylated p21Cip1/WAF1 in nuclei and display increased apoptosis. (A) Representative Western blots of PKCd, phospho-Ser146 p21Cip1/WAF1 and p21Cip1/WAF1 of control INS-1E cells and INS-1E cells treated with control siRNA or PKCd-specific siRNA and the respective densitometric analysis presented as means + SEM of n = 3 independent experiments. * (p,0.05) and ** (p,0.01) indicate significance to the respective band of control INS-1E cells set to 100%. (B) Percentage of p21Cip1/WAF1 positive nuclei analyzed by laser scanning microscopy is expressed as means + SEM of n = 3–4 independent experiments. (C–E) Percentage of TUNEL positive INS-1E cells treated with siRNA (C), control INS-1E cells, PKCdWT and PKCdKN INS-1E cells (D) and islet cells isolated from control mice, PKCdWT and PKCdKN transgenic mice (E) expressed as means + SEM of n = 3 independent experiments. * (p,0.05) indicates significance to the number of TUNEL- positive control INS-1E cells. doi:10.1371/journal.pone.0028828.g006 exogenous overexpression of p21Cip1/WAF1 in rat islets suppressed insulin biogenesis [42]. In the second study using a mouse model with deficient DNA repair reduced b-cell proliferation and the onset of diabetes was accompanied by increased expression of p21Cip1/WAF1 [43]. One difference which might explain these opposing results between the two latter studies and our cell models PLoS ONE | www.plosone.org 7 December 2011 | Volume 6 | Issue 12 | e28828