MiRNA-Dependent Regulation of AKT1 Phosphorylation.

Mallory I Frederick,Nileeka Balasuriya,Tarana Siddika,Matthew A Turk,Patrick O’Donoghue,Ilka U Heinemann,Pengcheng Zhang

doi:10.3390/cells11050821

Mallory I Frederick, Nileeka Balasuriya + Show 5 more

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https://doi.org/10.3390/cells11050821

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Journal: Cells	Publication Date: Feb 26, 2022
Citations: 11	License type: CC BY 4.0

Affiliation: Western University

Abstract

The phosphoinositide-3-kinase (PI3K)/AKT pathway regulates cell survival and is over-activated in most human cancers, including ovarian cancer. Following growth factor stimulation, AKT1 is activated by phosphorylation at T308 and S473. Disruption of the AKT1 signaling pathway is sufficient to inhibit the epithelial-mesenchymal transition in epithelial ovarian cancer (EOC) cells. In metastatic disease, adherent EOC cells transition to a dormant spheroid state, characterized previously by low S473 phosphorylation in AKT1. We confirmed this finding and observed that T308 phosphorylation was yet further reduced in EOC spheroids and that the transition from adherent to spheroid growth is accompanied by significantly increased levels of let-7 miRNAs. We then used mechanistic studies to investigate the impact of let-7 miRNAs on AKT1 phosphorylation status and activity in cells. In growth factor-stimulated HEK 293T cells supplemented with let-7a, we found increased phosphorylation of AKT1 at T308, decreased phosphorylation at S473, and enhanced downstream AKT1 substrate GSK-3β phosphorylation. Let-7b and let-7g also deregulated AKT signaling by rendering AKT1 insensitive to growth factor simulation. We uncovered let-7a-dependent deregulation of PI3K pathway components, including PI3KC2A, PDK1, and RICTOR, that govern AKT1 phosphorylation and activity. Together, our data show a new role for miRNAs in regulating AKT signaling.

Highlights

Epithelial ovarian cancer (EOC) has a 5-year relative survival rate of only 44%, making it the fifth most lethal cancer among women, largely attributed to high rates of metastasis
We found AKT1 signaling was deregulated in epidermal growth factor (EGF)-stimulated cells supplemented with let-7 miRNAs, which were characterized by enhanced AKT1 signaling, increased phosphorylation at T308, and decreased phosphorylation at S473 of AKT1
The dormant-toproliferative metastatic switch in EOC cells is directed by changes in AKT1 phosphorylation status [2,3]

Summary

Introduction

Epithelial ovarian cancer (EOC) has a 5-year relative survival rate of only 44%, making it the fifth most lethal cancer among women, largely attributed to high rates of metastasis. EOC cells survive in a dormant state, evading apoptosis and enabling metastasis. EOC cells utilize the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway to dynamically regulate the dormant-to-proliferative metastatic switch. The PI3K/AKT/mTOR pathway controls the phosphorylation and activation of the three AKT isoforms (protein kinase B, PKB), AKT1, AKT2, and AKT3 [1], and their downstream targets, where increased AKT phosphorylation and activity are major contributors to EOC pathogenicity [2,3]. Overexpression of the AKT isoforms is associated with multiple human cancers and hyper-activated AKT is a hallmark of > 50% of human tumors [4]. Despite their close sequence similarity, AKT1/2/3 have been shown to assume different roles, especially in cancer development. In mice, knockdown of AKT2 or AKT3 isoforms increases ovarian cancer metastasis and tumor

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