Identification of Juvenile Hormone-induced Posttranslational Modifications of Methoprene Tolerant and Krüppel Homolog 1 in the Yellow Fever Mosquito, Aedes Aegypti

Recent studies reported that JH-regulated phosphorylation status of the JH-receptor complex contributes to its transcription activity in Aedes aegypti. However, phosphorylation sites of these proteins have not yet been identified. In this study, we found that the fusion of an EGFP tag to Ae. aegypti Kr-h1 (AaKr-h1) and Met (AaMet) improved their stability in mosquito Aag-2 cells, which allowed their purification. The liquid chromatography and tandem mass spectrometry analysis of the purified AaKr-h1 showed that the phosphoserine residue at position 694, located in the evolutionarily conserved SVIQ motif, is dephosphorylated when the cells are exposed to JH. The AaKr-h1 dephosphorylation mutant (S694V) showed significantly higher activity in inducing the luciferase gene regulated by JH response elements. The phosphorylation profile of Met also changed after exposing Aag-2 cells to JH III. The Ser-77 and Ser-710 residues of Met were phosphorylated after JH III treatment. In contrast, the two phosphoserine residues at positions 73 and 747 were dephosphorylated after JH III treatment. JH exposure also induced transient and reversible phosphorylation of Thr-664 and Ser-723 residues. Overall, these data show that JH induces changes in post-translational modifications of AaMet and AaKr-h1. SIGNIFICANCE: Female Aedes aegypti mosquitoes are known to vector many disease agents, including Zika virus, dengue virus chikungunya virus, and Mayaro and yellow fever virus. In the present study, we developed an efficient method to prepare Ae. aegypti Met and Kr-h1, which are typically difficult to produce and purify, using a mosquito cell line expression system. A liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based approaches were utilized to map the phosphorylation profiles of the isolated proteins. We then monitored the changes induced by JH activation in the phosphorylation profiles to check if the JH modulates post-translation modification of its key transcription factors. We found that the JH induced alterations in the phosphorylation profiles of the multiple residues of AaMet. In contrast, activation of the JH signaling pathway was accompanied by dephosphorylation of AaKr-h1 at phosphoserine-694, increasing its transcriptional activity. In addition, S694 of AaKr-h1 was located in the RMSSVIQYA motif highly conserved in orthologous proteins from other insect species. These results can help us further understand how JH modulates its key transcription factors and provide a basis for the development of novel insect control strategies.