Effect of IRS4 Levels on PI 3-Kinase Signalling

Abstract

Insulin receptor substrate 1 (IRS1) and IRS2 are well-characterized adapter proteins that relay signals from receptor tyrosine kinases to downstream components of signalling pathways. In contrast, the function of IRS4 is not well understood. IRS4 overexpression has been associated with acute lymphoblastic leukaemia and subungual exostosis, while point mutations of IRS4 have been found in melanomas. Here, we show that while IRS4 expression is low in most cancer cell lines, IRS4 mRNA and protein levels are markedly elevated in certain cells including the NCI-H720, DMS114, HEK293T and HEK293AAV lines. Surprisingly, IRS4 expression was also strongly induced when HEK293 cells were infected with retroviral particles and selected under puromycin, making IRS4 expression a potential off-target effect of retroviral expression vectors. Cells with high expression of IRS4 displayed high phosphatidylinositol (3,4,5)-trisphosphate (PIP3) levels, as well as elevated Akt and p70 S6 kinase activities, even in the absence of growth factors. PI 3-kinase (PI3K) signalling in these cells depends on IRS4, even though these cells also express IRS1/2. Knockdown of IRS4 also inhibited cell proliferation in cells with high levels of IRS4. Together, these findings suggest IRS4 as a potential therapeutic target for cancers with high expression of this protein.

IRS4 induces mammary tumorigenesis and confers resistance to HER2-targeted therapy through constitutive PI3K/AKT-pathway hyperactivation

“…The IRS family is known to interact with many proteins, apart from the canonical p85 and GRB2, and can even form large multiprotein complexes (reviewed in refs 7, 50). Moreover, nuclear translocation with associated effects on, for example, DNA repair, rRNA synthesis and gene expression, has been reported for IRS proteins as well631515253, processes which also play a role in oncogenesis. Therefore, it may be useful to investigate these aspects in IRS4-induced tumours in the future.…”

“…8a-c). Although PI3K/AKT pathway activation by IRS4 has been described before3132, the underlying mechanism thus far remained largely unclear.…”

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.…”

“…IRS1 and IRS2 are expressed ubiquitously in the entire body, and knock-out of IRS1 or IRS2 in mice leads to severe phenotypes, such as marked growth retardation and diabetes, respectively (26 -28). Conversely, IRS4 is expressed only in specific tissues, such as the thymus, pituitary gland, and hypothalamus (29 -31), and cell lines, such as 293T, 293AAV, and HepG2 cells (22,32). IRS4 knock-out mice exhibit mild defects in growth, reproduction, glucose homeostasis, and maternal behaviors (31,33).…”

Roles of miR-196a on gene regulation of neuroendocrine tumor cells

“…The cells were cultured at 37°C and 5% CO2-humidified atmosphere in culture media. The cell lines have been previously used in a variety of studies, such as Hoxhaj et al, 2013, Randle et al, 2013and Rokstad et al, 2012 …”