Is Insulin Receptor Substrate4 (IRS4) a Platform Involved in the Activation of Several Oncogenes?

SIMPLE SUMMARY: IRS4 (insulin receptor substrate4) belongs to a family of intracellular proteins that include IRS1 and IRS2 and whose physiological function is to transmit the effects of insulin and IGF1 inside the cell. IRS4 is the least studied of this family, and its expression has recently been shown to be increased in many types of cancer. IRS4 serves to connect different signaling pathways, such as MAP kinases and PI3K/AKT. In addition, it has been observed that it is capable of activating several oncogenes, such as BRK (breast tumor kinase) and feline sarcoma-related protein (FER). Increased IRS4 expression in cancer cells may be due to changes in the regulatory region of the gene or increased chromosomal aberrations. Our objective has been to carry out a review to assess the possibility that IRS4 behaves as a meeting point for different oncogene signaling pathways, which we have called the oncogene platform. ABSTRACT: The IRS (insulin receptor substrate) family of scaffold proteins includes insulin receptor substrate-4 (IRS4), which is expressed only in a few cell lines, including human kidney, brain, liver, and thymus and some cell lines. Its N-terminus carries a phosphotyrosine-binding (PTB) domain and a pleckstrin homology domain (PH), which distinguishes it as a member of this family. In this paper, we collected data about the molecular mechanisms that explain the relevance of IRS4 in the development of cancer and identify IRS4 differences that distinguish it from IRS1 and IRS2. Search engines and different databases, such as PubMed, UniProt, ENSEMBL and SCANSITE 4.0, were used. We used the name of the protein that it encodes “(IRS-4 or IRS4)”, or the combination of these terms with the word “(cancer)” or “(human)”, for searches. Terms related to specific tumor pathologies (“breast”, “ovary”, “colon”, “lung”, “lymphoma”, etc.) were also used. Despite the lack of knowledge on IRS4, it has been reported that some cancers and benign tumors are characterized by high levels of IRS-4 expression. Specifically, the role of IRS-4 in different types of digestive tract neoplasms, gynecological tumors, lung cancers, melanomas, hematological tumors, and other less common types of cancers has been shown. IRS4 differs from IRS1 and IRS2 in that can activate several oncogenes that regulate the PI3K/Akt cascade, such as BRK and FER, which are characterized by tyrosine kinase-like activity without regulation via extracellular ligands. In addition, IRS4 can activate the CRKL oncogene, which is an adapter protein that regulates the MAP kinase cascade. Knowledge of the role played by IRS4 in cancers at the molecular level, specifically as a platform for oncogenes, may enable the identification and validation of new therapeutic targets.