Adenovirus 5 E1A is responsible for increased expression of insulin receptor substrate 4 in established adenovirus 5-transformed cell lines and interacts with IRS components activating the PI3 kinase/Akt signalling pathway

Abstract

Using mass spectrometric analysis insulin receptor substrate 4 (IRS-4) has been identified as a novel adenovirus 5 early region 1A (Ad5E1A)-binding protein. IRS-4 interacts with both the transcriptional activation domain (conserved region 3) and the N-terminal region of Ad5E1A13S. Prolonged expression of Ad5E1A13S is required for the observed dramatic increase in the levels of IRS-4 mRNA and protein in Ad5E1-transformed human cell lines. Once expressed, as well as binding to E1A and the insulin receptor, IRS-4 remains tyrosine phosphorylated and constitutively associates with the regulatory p85 subunit of phosphoinositide 3 kinase, resulting in the phosphorylation of Akt (causing activation) and GSK-3b (causing inhibition). Reducing IRS-4 expression using small interfering RNA (siRNA) in established Ad5E1A-expressing cell lines decreases the activation of Akt and cellular proliferation. During Ad5 infection, IRS-4 is not expressed. However, Ad5E1A associates with IRS-1, increasing Akt and GSK-3b phosphorylation and tyrosine phosphorylation of IRS-1 itself. We conclude that the association and altered regulation of IRS proteins by Ad5E1A contribute to the adenovirus-transformed phenotype and modulates viral infection in an Akt-dependent manner.

Effect of IRS4 Levels on PI 3-Kinase Signalling

“…Previously, IRS4 levels were shown to be elevated after adenovirus 5 E1A infection and transfections of cells [24]. Indeed, in searching for cell lines with high IRS4 expression, we noticed that the levels of IRS4 were markedly higher in HEK293 cells stably expressing the T antigen (293T) and adeno-associated virus (293AAV) than in parental HEK293 cells.…”

“…IRS4 has reported proliferative effects in human cell lines [21], [22]. IRS4 also interacts with adeno-associated viral proteins in infected cells and its expression is upregulated by adenoviral infection [23], [24].…”

Overexpressing cellular repressor of E1A-stimulated genes protects mesenchymal stem cells against hypoxia- and serum deprivation-induced apoptosis by activation of PI3K/Akt

“…It is well known that adenovirus E1A genes can strongly induce apoptosis in different cell types [10,11]. Potential connections between E1A signaling and multiple signaling pathways have been reported in many cell types; of these, the phosphatidylinositide 3-kinase (PI3K)/Akt pathway has been shown to respond to a variety of stimuli, including serum withdrawal, cell cycle disturbances, loss of cell adhesion and DNA damage, in a variety of cell types [12][13][14]. The PI3K/Akt pathways play important roles in mediating survival signaling in MSCs [15].…”

Insulin Receptor Substrate-4 Binds to Slingshot-1 Phosphatase and Promotes Cofilin Dephosphorylation

“…Previous studies showed that overexpression of IRS4 induces higher levels of phosphatidylinositol 3,4,5-trisphosphate, Akt activation, and cell proliferation even in the absence of insulin or growth factors and that knockdown of IRS4 suppresses Akt activation and cell proliferation (21,22). We also showed that knockdown of IRS4 reduced the levels of P-Akt (Thr-308 and Ser-473) and P-GSK3␣/-3␤ and that expression of IRS4 restored the levels of these phosphoproteins in IRS4-depleted cells.…”