Deciphering the Impact of AKT1 Pathogenic Variants in Juvenile Granulosa Cell Tumors Using a Drosophila Model.

Juvenile-type granulosa cell tumors (JGCTs) manifest during the prepubertal period as precocious pseudo-puberty and/or dysmenorrhea. We have previously identified pathogenic variants in AKT1 in JGCTs. This study aims to understand how these variants affect cellular function at the phenotypic and molecular levels using a Drosophila model. Transgenic Drosophila models expressing WT AKT1 and four pathogenic variants were created under the control of tissue-specific promoters. Phenotypic effects were studied by assessing Drosophila wings for cell division and growth using wing surface and trichome density and ovarian follicular cells were examined for subcellular localization and morphology. Molecular analyses included mass spectrometry to identify differentially expressed proteins (DEPs) and phospho-peptides, along with RNA-Seq to characterize transcriptomic changes. Wings expressing mutated AKT1 showed increased surface area and reduced trichome density, indicating larger cells. In ovarian follicular cells, WT AKT1 localized primarily to the cytoplasm, while mutated AKT1 variants were associated with the plasma membrane, leading to morphological abnormalities and increased cell size. Mass spectrometry revealed numerous DEPs and phospho-peptides, highlighting changes in pathways such as glycolysis and Rho GTPase signaling. Transcriptomics demonstrated a clear gain of function for mutated AKT1 in activating a subset of genes. However, several genes upregulated by WT AKT1 were less effectively activated by the mutants, indicating a potential loss-of-function in transcriptional regulation for this subset, revealing an unexpected mechanistic complexity. Network analysis of interactions involving DEPs, phosphorylated proteins, and transcription factors suggests these elements mediate the observed proteomic and transcriptional alterations. Taken together, the results underscore the utility of Drosophila models in unraveling the biological relevance of AKT1 pathogenic variants in cancer.