Insulin-receptor substrate proteins

Yenush L, Fernandez R, Myers MG Jr et al 1996 The Drosophila insulin receptor activates multiple signaling pathways but requires insulin receptor substrate proteins for DNA... 

Miyakawa, Y. Rojnuckarin, P. Habib, T. Kaushansky, K. Thrombopoietin induces phosphoinositol 3-kinase activation through SHP2, Gab, and insulin receptor substrate proteins in BAF3 cells and primary murine megakaryocytes. J. Biol. Chem., 276, 2494-2502 (2001)... 

Clancy, D., Gems, D., Harshman, L. G., Oldham, S., Stocker, H., Hafen, E., Leevers, S. J. and Partridge, L. Extension of lifespan by loss of CHICO, a Drosophila insulin receptor substrate protein. Science 292 104-106 2001. 

David J. Clancy, David Gems, Lawrence G. Harshman, Sean Oldham, Hugo Stocker, Ernst Hafen, Sally J. Leevers, Linda Partridge, Extension of Life-Span by Loss of CHICO, a Drosophila Insulin Receptor Substrate Protein, Science, 292 (2001), 104-106. 

How insulin receptor substrate proteins regulate the metabolic capacity of the liver—implications for health and disease. 2008. CurrMed Chem, 15, 1316—1329. 

Insulin Receptor. Figure 1 Structure and function of the insulin receptor. Binding of insulin to the a-subunits (yellow) leads to activation of the intracellular tyrosine kinase ((3-subunit) by autophosphorylation. The insulin receptor substrates (IRS) bind via a phospho-tyrosine binding domain to phosphorylated tyrosine residues in the juxtamembrane domain of the (3-subunit. The receptor tyrosine kinase then phosphorylates specific tyrosine motifs (YMxM) within the IRS. These tyrosine phosphorylated motifs serve as docking sites for some adaptor proteins with SRC homology 2 (SH2) domains like the regulatory subunit of PI 3-kinase. 

The catalytic pi 10 subunit has four isoforms, all of which contain a kinase domain and a Ras interaction site. In addition, the a, (3, and y isoforms possess an interaction site for the p85 subunit. The class I enzymes can be further subdivided class IA enzymes interact through their SH2 domains with phosphotyrosines present on either protein tyrosine kinases or to docking proteins such as insulin-receptor substrates (IRSs GAB-1) or linkers for activation of T cells (LATs in the case of T cells). 

Once autophosphorylation begins, a complex of other events ensues. An insulin receptor substrate (IRS-1) binds the receptor and is phosphorylated on tyrosine residues, allowing proteins with SH2 (src homology) domains to bind to the. phosphotyrosine residues on IRS-1 and become active. In this way, the receptor activates several enzyme cascades, which involve ... 

Answen Q Proteins with SH2 domains might bind to the insulin receptor substrate-1 (IRS-1) to transmit signals from the insulin receptor, a tyrosine kinase type of receptor. PI-3 kinase is an example of an SH2 domain protein. SH2 domains are not involved in DNA binding (choices A and D). Examples of protein domains that bind DNA include zinc fingers (steroid receptors), leudne zippers (CREB protein), and helix-turn-helbc proteins (homeodomain proteins),... 

The effects of insulin on transcription are shown on the left of the illustration. Adaptor proteins Crb-2 and SOS ( son of sevenless ) bind to the phosphorylated IRS (insulin-receptor substrate) and activate the G protein Ras (named after its gene, the oncogene ras see p.398). Ras activates the protein kinase Raf (another oncogene product). Raf sets in motion a phosphorylation cascade that leads via the kinases MEK and ERK (also known as MARK, mitogen-activated protein kinase ) to the phosphorylation of transcription factors in the nucleus. 

Activation of the enzyme PIS kinase (PI3K) constitutes a third pathway of Trk receptor signaling. The precise mechanism by which PI3K activation occurs has not yet been completely elucidated, but appears to involve Trk activation of intermediate proteins, such as insulin receptor substrate (IRS)-1,2 and the IRS-like protein Gabl. Downstream of PI3K activation is stimulation of the kinase Akt, which is largely responsible for the survival effects mediated by this pathway. 

The insulin receptor is composed of two heterodimers each heterodimer is composed of an a unit and a P unit. The a unit is extracellular and contains the insulin recognition and binding sites the p unit spans the cellular membrane and contains a tyrosine kinase. Although insulin can bind to a single ap dimer, it binds with higher affinity to the aPaP tetrameric complex. When insulin binds to an a unit, the tyrosine kinase associated with the corresponding p unit is stimulated. Following this, intracellular proteins such as IRS-1 and IRS-2 (IRS=insulin receptor substrate) are phosphorylated by the P subunit tyrosine kinase, and they in turn activate a network of phosphorylations within the receptor cell. 

Fig. 8.20. Modular composition of adaptor proteins. Adaptor proteins do not show any enzyme activity of their own, but rather they contain protein modules which help to bind signal proteins into signal pathways. IRS-1 insulin receptor substrate 1 PTB phosphotyrosine binding domain PH pleckstrin homology domain P phosphotyrosine-containing binding site for SH2 or PTB domains HLH helrx-loop-hehx DNA binding motif...

The insulin receptor substrate IRS couples the insulin receptor to sequential effector molecules (review Ogawa et al., 1998). On binding of insulin to the insulin receptor, the tyrosine kinase activity of the receptor is stimulated. The IRS protein is phosphory-lated at several Tyr residues, which then serve as attachment points for sequential effector molecules as e.g. the Grb2-mSos complex, the P13-kinase and the protein tyrosine phosphatase SHP-2. The IRS protein also has a phosphotyrosine binding domain and a PH domain. Both modules are required for signal transduction in vivo. It is assumed that the PTB domain binds to autophosphorylation sites of the insulin receptor and that the PH domain is involved in membrane association of IRS. 

Schematic diagram of the insulin receptor heterodimer in the activated state. IRS, insulin receptor substrate MAP, mitogen-activated protein P, phosphate tyr, tyrosine.

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