Npas4 is a stress-induced factor in pancreatic β-cells. Npas4 expression was induced in a dose-dependent manner in MIN6 cells by a 24-h exposure to the ER calcium–depleting drug thapsigargin
(n = 3–6) (A). However, in 1 µmol/L thapsigargin, the Npas4 response is dynamic, with markedly higher expression at 1 and 24 h at the
message level (B) and 24 h at the protein level (n = 3) (C). Npas4 was also induced in a dose-dependent manner by palmitate with maximum expression between 1 and 2 h at both the message (D) and protein (n = 3) (E) levels in response to 500 µmol/L palmitate. Elevated expression was maintained through 24 h (compare D and E) (n = 3). In mouse islets, Npas4 expression was increased after 24-h exposure to 1 µmol/L thapsigargin (F) and 500 µmol/L palmitate (n = 3) (G) in 11 mmol/L glucose RPMI. Significance was established using two-tailed Student t tests or a one-way ANOVA with Dunnett post hoc analysis where applicable. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.