Induction of insulin production in rat pancreatic acinar carcinoma cells by conophylline.
We set up a screening system to detect low-molecular-weight compounds that induce insulin expression in pancreatic acinar carcinoma AR42J cells. They can differentiate into insulin-producing cells with neuron-like morphological change when treated with activin A. We employed this morphological change for the screening of beta-cell inducers among various signal transduction inhibitors. As a result, a vinca alkaloid, conophylline, induced neurite formation at 0.1 approximately 0.3 microg/ml in 72 h, like activin A. Conophylline-treated cells were found to express insulin as measured at both mRNA and protein levels. By RT-PCR analysis, conophylline-treated cells were shown to express neurogenin3 strongly. They also expressed Beta2/NeuroD and Nkx2.2, but not Pax4 and PP. Although activin A induces nuclear translocation of Smad2, conophylline did not. But the latter induced p38 activation, like activin A, as detected by phosphorylation. Pretreatment with a p38-specific inhibitor, SB203580, lowered the conophylline-induced insulin production. Therefore, p38 activation would be involved in the differentiation of AR42J cells into insulin-producing cells. Studies on structure-activity relationship with conophyllidine, conofoline, conophyllinine, and related monomer alkaloids showed that the dimeric aspidosperma structure with the dihydrofuran unit in its center was essential for the differentiation-inducing activity.