The Steroid Hormone 20-hydroxyecdysone Upregulates Calcium Release-activated Calcium Channel Modulator 1 Expression to Induce Apoptosis in the Midgut of Helicoverpa Armigera

Animal steroid hormones stimulate extracellular Ca influx into cells; however, the mechanism remains unclear. In this study, we determined that the Ca influx induced by steroid hormone 20-hydroxyecdysone (20E) is mediated by the calcium release-activated calcium channel modulator 1 (CRACM1/Orai1). The Orai1 mRNA is highly expressed during midgut programmed cell death in the lepidopteran insect Helicoverpa armigera. 20E upregulated the expression of Orai1 in H. armigera larvae and in an epidermal cell line (HaEpi). Knockdown of Orai1 in HaEpi cells blocked 20E-induced Ca influx, and the inhibitor of inositol 1, 4, 5-trisphosphate receptor (IPR) Xestospongin (XeC) blocked 20E-induced Ca influx, suggesting that 20E, via Orai1, induces stored-operated Ca influx. Orai1 interacts with stromal interaction molecule 1(Stim1) to exert its function in 20E-induced Ca influx. 20E promotes Orai1 aggregation through G-protein-coupled receptors, phospholipase C gamma 1, and Stim1. Knockdown of Orai1 in the HaEpi cell line repressed apoptosis and maintained autophagy under 20E regulation. Knockdown of Orai1 in larvae delayed pupation, repressed midgut apoptosis, maintained the midgut in an autophagic state, and repressed 20E-pathway gene expression. These results revealed that steroid hormone 20E, via Orai1, induces Ca influx to promote the transition of midgut from autophagy to apoptosis.