Expression of Human Mutant Preproinsulins Induced Unfolded Protein Response, Gadd45 Expression, JAK-STAT Activation, and Growth Inhibition in Drosophila

Abstract

Mutations in the insulin gene (INS) are frequently associated with human permanent neonatal diabetes mellitus. However, the mechanisms underlying the onset of this genetic disease is not sufficiently decoded. We induced expression of two types of human mutant INSs in Drosophila using its ectopic expression system and investigated the resultant responses in development. Expression of the wild-type preproinsulin in the insulin-producing cells (IPCs) throughout the larval stage led to a stimulation of the overall and wing growth. However, ectopic expression of human mutant preproinsulins, hINSC96Y and hINSLB15YB16delinsH, neither of which secreted from the β-cells, could not stimulate the Drosophila growth. Furthermore, neither of the mutant polypeptides induced caspase activation leading to apoptosis. Instead, they induced expression of several markers indicating the activation of unfolded protein response, such as ER stress-dependent Xbp1 mRNA splicing and ER chaperone induction. We newly found that the mutant polypeptides induced the expression of Growth arrest and DNA-damage-inducible 45 (Gadd45) in imaginal disc cells. ER stress induced by hINSC96Y also activated the JAK-STAT signaling, involved in inflammatory responses. Collectively, we speculate that the diabetes-like growth defects appeared as a consequence of the human mutant preproinsulin expression was involved in dysfunction of the IPCs, rather than apoptosis.

Loss of Paip1 causes translation reduction and induces apoptotic cell death through ISR activation and Xrp1

“…To examine which one of the two kinases mediates the effects of Paip1 depletion on the ISR, we knocked down individually PERK and GCN2 in a Paip1 depletion background using hh-Gal4 . Previous reported RNAi lines for PERK and GCN2 were used for this analysis [ 37 – 39 ]. We found that heightened eIF2α phosphorylation in Paip1 -deficient cells was brought to normal levels by PERK knockdown (Fig.…”