AKT1E17K-interacting lncRNA SVIL-AS1 promotes AKT1 oncogenic functions by sustaining its phosphorylation

AKT1 E17K, occurring at low frequency in a broad range of cancer types, is a gain-of-function mutation that constitutively activates the PI3K-AKT pathway. However, how AKT1E17K is regulated in cancer pathogenesis remains elusive. Here, we interrogate the AKT1E17K-interacting lncRNAs and identify that SVIL-AS1 preferentially binds to AKT1E17K rather than AKT1WT proteins. We find that SVIL-AS1 enhances AKT1 phosphorylation and downstream signaling. SVIL-AS1 knockdown dramatically inhibits the growth of AKT1E17K cells in intro and in vivo. Notably, AKT1 and SVIL-AS1 interaction is AKT1 phosphorylation-dependent. SVIL-AS1 also interacts with PPP2R2A, a subunit of phosphatase PP2A holoenzyme, and blocks the binding of PPP2R2A to AKT1E17K to prevent AKT1 dephosphorylation. Moreover, AKT1E17K cells are not effectively inhibited by the allosteric AKT inhibitor, whereas silencing SVIL-AS1 sensitizes AKT1E17K cells to AKT1 allosteric inhibitor, as well as the PI3K inhibitor. In breast cancer tissues, SVIL-AS1 is highly expressed and associated with p-AKT1 level and poor prognosis of patients. Together, our findings highlight a previously unappreciated role of lncRNA SVIL-AS1 in regulating AKT1 dephosphorylation, which serves as a promising therapeutic target for AKT1E17K tumors. To identify lncRNAs binding to the AKT1 E17K mutant protein, we transfected Flag-tagged AKT1 wild-type (AKT1WT) or E17K mutant (AKT1E17K) plasmids into breast cancer cell line MDA-MB-231. RNA immunoprecipitation (RIP) using negative control IgG or anti-FLAG antibody respectively was then performed and deep sequencing showed that several lncRNAs preferentially bound to the AKT1 E17K mutant protein.