Interleukin-13 signal transduction in lymphohemopoietic cells. Similarities and differences in signal transduction with interleukin-4 and insulin

Insulin stimulates the serine phosphorylation of the signal transducer and activator of transcription (STAT3) isoform

Insulin stimulation of Chinese hamster ovary cells expressing the human insulin receptor and differentiated 3T3L1 adipocytes resulted in a time-dependent reduction in the SDS-polyacrylamide gel electrophoretic mobility of STAT3. The decreased STAT3 mobility initially occurred by 2 min and was quantitative by 5 min. In addition, the change in STAT3 mobility was concentration-dependent and was detectable at 0.3 nm insulin with maximal effect between 1 and 3 nm. Although both these cell types also express the STAT1 alpha, STAT1 beta, STAT5, and STAT6 isoforms, only STAT3 was observed to undergo an insulin-dependent reduction in mobility. Immuno-precipitation of STAT1 and STAT3 from 32P-labeled cells demonstrated that only STAT3 was phosphorylated in response to insulin whereas phosphoamino acid analysis indicated that this phosphorylation event occurred exclusively on serine residues. Furthermore, treatment of cell extracts with alkaline phosphatase reversed the insulin-stimulated decrease in STAT3 mobility. Together, these data demonstrate that insulin is a specific activator of STAT3 serine phosphorylation without affecting the other STAT isoforms.

The Fyn tyrosine kinase binds Irs-1 and forms a distinct signaling complex during insulin stimulation

Irs-proteins link the receptors for insulin/IGF-1, growth hormones, and several interleukins and interferons to signaling proteins that contain Src homology-2 (SH2). To identify new Irs-1-binding proteins, we screened a mouse embryo expression library with recombinant [32P]Irs-1, which revealed a specific association between p59fyn and Irs-1. The SH2 domain in p59fyn bound to phosphorylated Tyr895 and Tyr1172, which are located in YXX(L/I) motifs. Mutation of p59fyn at the COOH-terminal tyrosine phosphorylation site (Tyr531) enhanced its binding to Irs-1 during insulin stimulation. Binding experiments with various SH2 protein revealed that Grb-2 was largely excluded from Irs-1 complexes containing p59fyn, whereas Grb-2 and p85 occurred in the same Irs-1 complex. By comparison with the insulin receptor, p59fyn kinase phosphorylated a unique cohort of tyrosine residues in Irs-1. These results outline a role for p59fyn or other related Src-kinases during insulin and cytokine signaling.

Growth inhibition signalled through the interleukin-4/interleukin-13 receptor complex is associated with tyrosine phosphorylation of insulin receptor substrate-1

Induction of growth inhibition in human colorectal carcinoma cell lines by interleukin (IL)-4 and IL-13 was associated with the neophosphorylation of a 170 kDa cellular protein, identified as insulin receptor substrate-1 (IRS-1) by immunoprecipitation. Tyrosine phosphorylation of IRS-I was also induced by insulin and insulin-like growth factor I. Sublines of colorectal carcinoma cells unresponsive to growth modulation by IL-4, IL-13 or insulin-like growth factor I-induced growth did not phosphorylate IRS-1. A functional, multimeric IL-4 receptor complex was present on all carcinoma cell lines with a subunit composition of 65 kDa, 75 kDa and the previously characterized 130 kDa band as demonstrated by affinity cross-link with 126I labelled IL-4. The 65 kDa subunit is novel whereas the 75 kDa band represents the common IL-2 receptor gama-chain the novel 65 kDa receptor was present as a double band and bound primarily 125I-labelled IL-13. The present study demonstrates the involvement of a novel chain other than the gama-chain in the receptor complexes of IL-4 and IL-13 and and post-receptor tyrosine phosphorylation of IRS-1. The association of IRS-1 with growth inhibitory signals in carcinoma cells suggests a novel mechanism of tumour growth control.

Insulin receptor substrate-2 binds to the insulin receptor through its phosphotyrosine-binding domain and through a newly identified domain comprising amino acids 591-786

We compared the interaction between the insulin receptor (IR) and the IR substrate (IRS) proteins IRS-1 and IRS-2) using the yeast two-hybrid system. Both IRS proteins interact specifically with the cytoplasmic portion of the IR and the related insulin-like growth factor-I receptor, and these interactions require receptor tyrosine kinase activity. Alignment of IRS-1 and IRS-2 revealed two conserved domains at the NH2 terminus, called IH1PH and IH2PTB, which resemble a pleckstrin homology (PH) domain and a phosphotyrosine binding (PTB) domain, respectively. The IH2PTB binds to the phosphorylated NPXY motif (Tyr-960) in the activated insulin receptor, providing a specific mechanism for the interaction between the receptor and IRS-1. Although the IH2PTB of IRS-2 also interacts with the NPEY motif of the insulin receptor, it is not essential for the interaction between the insulin receptor and IRS-2 in the yeast two-hybrid system. IRS-2 contains another interaction domain between residues 591 and 786, which is absent in IRS-1. This IRS-2-specific domain is independent of the IH2PTB and does not require the NPEY motif; however, it requires a functional insulin receptor kinase and the presence of three tyrosine phosphorylation sites in the regulatory loop (Tyr-1146, Tyr-1150, and Tyr-1151). Importantly, this novel domain mediates the association between IRS-2 and insulin receptor lacking the NPXY motif and may provide a mechanism by which the stoichiometry of regulatory loop autophosphorylation enhances IRS-2 phosphorylation.

IL-4 and IL-13 receptors: are they one and the same?

Interleukin 4 (IL-4) and IL-13 share several biological properties, suggesting that they also share a common receptor or receptor component. Indeed, as discussed here by Robin Callard and colleagues, the IL-13 receptor appears to be a functional receptor for IL-4.

Characterization and cloning of a 58/53-kDa substrate of the insulin receptor tyrosine kinase

A monoclonal antibody has been produced which immunoprecipitates 58- and 53-kDa proteins which are rapidly tyrosine phosphorylated in insulin-treated cells. These proteins can also be tyrosine phosphorylated in vitro by the isolated human insulin receptor. Increased tyrosine phosphorylation of these proteins is also observed in cells expressing a transforming chicken c-Src (mutant Phe-527) and in cells with the activated tyrosine kinase domains of the Drosophila insulin receptor, human insulin-like growth factor I receptor, and human insulin receptor-related receptor. P58/53 did not appear to associate with either the GTPase activating protein of Ras (called GAP) or the phosphatidylinositol 3-kinase by either co-immunoprecipitation experiments or in Far Westerns with the SH2 domains of these two proteins. Since p58/53 did not appear, by immunoblotting, to be related to any previously described tyrosine kinase substrate such as the SH2 containing proteins SHC and the tyrosine phosphatase Syp, the protein was purified in sufficient amounts to obtain peptide sequence. This sequence was utilized to isolate a cDNA clone that encodes a previously uncharacterized 53-kDa protein which, when expressed in mammalian cells, is tyrosine phosphorylated by the insulin receptor.

Signal transduction pathway of interleukin-4 and interleukin-13 in human B cells derived from X-linked severe combined immunodeficiency patients

Interleukin-4 (IL-4) and IL-13 are functionally similar cytokines. The functional IL-4 receptor (IL-4R) consists of the IL-4R alpha chain (IL-4R alpha) and the IL-2R gamma chain (gamma c), which is shared by the IL-2, IL-7, IL-9, and IL-15 receptors. The functional IL-13R is thought to involve the IL-4R alpha but not gamma c. In this study, we have analyzed activation of members of the Janus tyrosine kinase (Jak) family and signal transducers and activators of transcription (STAT) 6 induced by IL-4 and IL-13 in Epstein-Barr virus-transformed B cells derived from two patients of X-linked severe combined immunodeficiency, who have mutations of the gamma c gene in the extracellular and intracellular domains. In these B cells, IL-4 failed to induce tyrosine phosphorylation of Jak3 and activation of STAT6, or activation of these molecules was significantly decreased compared with Epstein-Barr virus-transformed normal B cells. In contrast, IL-13 activated STAT6 in these cells as well as normal B cells. However, Jak3 was not activated by IL-13, even in normal B cells. These results clearly indicated that gamma c is essential for activation of Jak3 and STAT6 in the signal transduction pathway of IL-4 in human B cells and that IL-13 does not utilize gamma c but activates STAT6 through an alternative pathway, which is not impaired in B cells of X-linked severe combined immunodeficiency patients.

Role of IRS-2 in insulin and cytokine signalling

The protein IRS-1 acts as an interface between signalling proteins with Src-homology-2 domains (SH2 proteins) and the receptors for insulin, IGF-1, growth hormone, several interleukins (IL-4, IL-9, IL-13) and other cytokines. It regulates gene expression and stimulates mitogenesis, and appears to mediate insulin/IGF-1-stimulated glucose transport. Thus, survival of the IRS-1-/- mouse with only mild resistance to insulin was surprising. This dilemma is provisionally resolved with our discovery of a second IRS-signalling protein. We purified and cloned a likely candidate called 4PS from myeloid progenitor cells and, because of its resemblance to IRS-1, we designate it IRS-2. Alignment of the sequences of IRS-2 and IRS-1 revealed a highly conserved amino terminus containing a pleckstrin-homology domain and a phosphotyrosine-binding domain, and a poorly conserved carboxy terminus containing several tyrosine phosphorylation motifs. IRS-2 is expressed in many cells, including tissues from IRS-1-/- mice, and may be essential for signalling by several receptor systems.