Npas4 induction is cytoprotective for pancreatic β-cells. Npas4 overexpression (black bars) in MIN6 cells (A, B, and D) significantly reduced Ddit3 induction after both thapsigargin (n = 3–10) (A) and palmitate (n = 3–5) (B) exposure. C and D: The reductions observed at the message level were also present at the protein level as adenoviral transduction with Npas4
(Np) decreased thapsigargin-mediated Ddit3 induction compared with controls (Ce) (n = 3–4). Knockdown of Npas4 with siRNAs did not alter basal Ddit3 expression but, after palmitate exposure, significantly
increased Ddit3 levels (n = 4) (E). A possible mechanism for the reduced Ddit3 induction is due to significant increases of the cytoprotective proteins BiP and Wfs-1 (n = 3) (F and G). Less Ddit3 induction in response to thapsigargin (n = 6–11) (H) or palmitate (n = 3–4) (I) was observed in mouse pancreatic islets after Ad-Npas4 transduction. The reductions in Ddit3 mRNA and protein translated
to significantly reduced TUNEL+ apoptotic MIN6 cells in Ad-Npas4–infected cells treated with either 1 or 10 μmol/L thapsigargin (n = 3) (J). Significance was determined using two-tailed Student t tests. *P ≤ 0.05; **P ≤ 0.01.