Identification of G protein subunit alpha i3 as a promising oncotarget of LUAD

Exploring new oncotargets essential for lung adenocarcinoma (LUAD) cell growth is important. Here the bioinformatical studies revealed that G alpha i3 expression is elevated in LUAD tissues and its overexpression correlates with poor survival of the patients. Moreover, overexpression of G alpha i3 mRNA and protein was detected in LUAD tissues of patients as well as in primary/immortalized LUAD cells. In both primary and immortalized LUAD cells, genetic silencing (by viral shRNA) or knockout ("KO", through CRISPR/Cas9 method) of G alpha i3 potently inhibited LUAD cell proliferation and mobility. The results of caspase-3 activity assay, caspase-9 activity assay, histone DNA ELISA, TUNEL nuclear staining and Annexin V staining showed that inhibition of G alpha i3 expression promoted apoptosis. In addition, a significant decrease in mitochondrial membrane potential was found in G alpha i3-deficient LUAD cells by JC-1 staining. Overexpression of G alpha i3 strengthened the proliferation and migration of LUAD cell. Gene set enrichment analysis revealed that G alpha i3 was closely related to PI3k/Akt/mTOR, which we validated experimentally. Akt-S6K phosphorylation was downregulated following G alpha i3 silencing or KO, but augmented after G alpha i3 overexpression in primary LUAD cells. Restoring Akt-S6K phosphorylation by a S473D constitutively- active mutant Akt1 ameliorated G alpha i3 KO-induced LUAD cell proliferation inhibition, migration suppression and apoptosis. In vivo, the growth of subcutaneous LUAD xenografts was largely inhibited after intratumoral injection of G alpha i3 shRNA-expressing adeno-associated virus (AAV). G alpha i3 downregulation, Akt-mTOR inhibition, proliferation inactivation and apoptosis were detected in the G alpha i3 shRNA-treated LUAD xenografts. Together, targeting G alpha i3 potently inhibited LUAD cell growth in vitro and in vivo.