HEIX1 Mutation Effects on Endoplasmic Reticulum Stress, Caspase Activation, and JNK2 Pathways

Background and Objective: Schneider 2 (S2) cells, derived from Drosophila melanogaster, are extensively utilized in developmental biology and genetics engineering research. Proper tissue formation depends on the regulation of developmental signalling, with the unfolded protein response (UPR) and autophagy playing critical roles in maintaining endoplasmic reticulum (ER) and mitochondrial homeostasis. Mutations in the HEIX1 gene disrupt these processes, triggering activation of the P-ERK and JNK signalling pathways, which lead to ER stress, mitochondrial dysfunction, and apoptosis. This study examines the molecular mechanisms underlying HEIX1 loss-of-function mutations in S2 cells, focusing on P-ERK and JNK pathway activation and their effects on cellular stress responses. Methods: This experimental study includes four groups of S2 cells, with 10 samples per group: (1) wild-type (WT) control, (2) HEIX1 homozygous mutant (HEIX1−/−), (3) HEIX1 heterozygous rescue group (*heix1/Df; UAS, Gal4, tubp>HEIX1), and (4) a group treated with the P-ERK inhibitor GSK. Protein extraction and analysis were performed across all groups. Variables such as P-ERK and JNK activation, reactive oxygen species (ROS) levels, apoptosis markers (caspase 9 activation), and UPR-related gene expression (GRP78 and CHOP) were measured using western blotting, immunofluorescence, and ROS assays. Findings: Loss of HEIX1 function significantly activated the P-ERK pathway, as evidenced by increased P-ERK phosphorylation, caspase 9 activation, and apoptosis. Mutants showed disrupted ER and mitochondrial homeostasis, including swelling and oxidative stress. Rescuing HEIX1 restored normal signalling and reduced apoptosis. P-ERK inhibition accelerated apoptosis and suppressed UPR-related gene expression, underscoring HEIX1's role in proteostasis. Conclusion: According to the results of this study, the HEIX1 gene is essential for maintaining ER and mitochondrial homeostasis, regulating stress responses, and preventing apoptosis. Its loss leads to P-ERK pathway activation, ER stress, and cell death. These findings provide insights into Drosophila development and the broader implications of HEIX1 in understanding human diseases linked to ER stress and apoptosis.