Effect of tyrosine mutations on the kinase activity and transforming potential of an oncogenic human insulin-like growth factor I receptor

Insulin Receptor Isoforms and Insulin Growth Factor-like Receptors: Implications in Cell Signaling, Carcinogenesis, and Chemoresistance

This comprehensive review thoroughly explores the intricate involvement of insulin receptor (IR) isoforms and insulin-like growth factor receptors (IGFRs) in the context of the insulin and insulin-like growth factor (IGF) signaling (IIS) pathway. This elaborate system encompasses ligands, receptors, and binding proteins, giving rise to a wide array of functions, including aspects such as carcinogenesis and chemoresistance. Detailed genetic analysis of IR and IGFR structures highlights their distinct isoforms, which arise from alternative splicing and exhibit diverse affinities for ligands. Notably, the overexpression of the IR-A isoform is linked to cancer stemness, tumor development, and resistance to targeted therapies. Similarly, elevated IGFR expression accelerates tumor progression and fosters chemoresistance. The review underscores the intricate interplay between IRs and IGFRs, contributing to resistance against anti-IGFR drugs. Consequently, the dual targeting of both receptors could present a more effective strategy for surmounting chemoresistance. To conclude, this review brings to light the pivotal roles played by IRs and IGFRs in cellular signaling, carcinogenesis, and therapy resistance. By precisely modulating these receptors and their complex signaling pathways, the potential emerges for developing enhanced anti-cancer interventions, ultimately leading to improved patient outcomes.

IGF1 receptor signaling pathways

Insulin-like growth factors (IGFs) bind specifically to the IGF1 receptor on the cell surface of targeted tissues. Ligand binding to the α subunit of the receptor leads to a conformational change in the β subunit, resulting in the activation of receptor tyrosine kinase activity. Activated receptor phosphorylates several substrates, including insulin receptor substrates (IRSs) and Src homology collagen (SHC). Phosphotyrosine residues in these substrates are recognized by certain Src homology 2 (SH2) domain-containing signaling molecules. These include, for example, an 85 kDa regulatory subunit (p85) of phosphatidylinositol 3-kinase (PI 3-kinase), growth factor receptor-bound 2 (GRB2) and SH2-containing protein tyrosine phosphatase 2 (SHP2/Syp). These bindings lead to the activation of downstream signaling pathways, PI 3-kinase pathway and Ras-mitogen-activated protein kinase (MAP kinase) pathway. Activation of these signaling pathways is known to be required for the induction of various bioactivities of IGFs, including cell proliferation, cell differentiation and cell survival. In this review, the well-established IGF1 receptor signaling pathways required for the induction of various bioactivities of IGFs are introduced. In addition, we will discuss how IGF signals are modulated by the other extracellular stimuli or by themselves based on our studies.

Heterogeneous Stromal Signaling within the Tumor Microenvironment Controls the Metastasis of Pancreatic Cancer

Understanding how stromal signals regulate the development of pancreatic ductal adenocarcinoma (PDAC) may suggest novel therapeutic interventions in this disease. In this study, we assessed the metastatic role of stromal signals suggested to be important in the PDAC microenvironment. Src and IGF-1R phosphorylated the prometastatic molecule Annexin A2 (AnxA2) at Y23 and Y333 in response to stromal signals HGF and IGF-1, respectively, and IGF-1 expression was regulated by the Sonic Hedgehog (Shh) pathway. Both Shh and HGF were heterogeneously expressed in PDAC stroma, and only dual inhibition of these pathways could significantly suppress AnxA2 phosphorylation, PDAC growth, and metastasis. Taken together, our results illuminate tumor-stromal interactions, which drive metastasis, and provide a mechanism-based rationale for a stroma-directed therapy for PDAC. Cancer Res; 77(1); 41-52. ©2016 AACR.

Sodium L-ascorbate enhances elastic fibers deposition by fibroblasts from normal and pathologic human skin

BACKGROUND

Vitamin C (L-ascorbic acid), a known enhancer of collagen deposition, has also been identified as an inhibitor of elastogenesis.

OBJECTIVE

Present studies explored whether and how the L-ascorbic acid derivative (+) sodium L-ascorbate (SA) would affect production of collagen and elastic fibers in cultures of fibroblasts derived from normal human skin and dermal fat, as well as in explants of normal human skin, stretch-marked skin and keloids.

METHODS

Effects of SA on the extracellular matrix production were assessed quantitatively by PCR analyses, western blots, biochemical assay of insoluble elastin and by immuno-histochemistry. We also evaluated effects of SA on production of the reactive oxygen species (ROS) and phosphorylation of IGF-I and insulin receptors.

RESULTS

SA, applied in 50-200 μM concentrations, stimulates production of both collagen and elastic fibers in all tested cultures. Moreover, combination of SA with a proline hydroxylase inhibitor induces a beneficial remodelling in explants of dermal scars, resulting in the inhibition of collagen deposition and induction of new elastogenesis. Importantly, we revealed that SA stimulates elastogenesis only after intracellular influx of non-oxidized ascorbate anions (facilitated by the sodium-dependent ascorbate transporter), that causes reduction of intracellular ROS, activation of c-Src tyrosine kinase and the enhancement of IGF-1-induced phosphorylation of the IGF-1 receptor that ultimately triggers elastogenic signalling pathway.

CONCLUSION

Our results endorse the use of this potent stimulator of collagen and elastin production in the treatment of wrinkled and stretch-marked skin. They also encourage inclusion of SA into therapeutic combinations with collagenogenesis inhibitors to prevent formation of dermal scars and keloids.

Molecular and functional characterizations of the association and interactions between nucleophosmin-anaplastic lymphoma kinase and type I insulin-like growth factor receptor

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is aberrantly expressed in a subset of T cell lymphoma that commonly affects children and young adults. NPM-ALK possesses significant oncogenic potential that was previously documented using in vitro and in vivo experimental models. The exact mechanisms by which NPM-ALK induces its effects are poorly understood. We have recently demonstrated that NPM-ALK is physically associated with type I insulin-like growth factor receptor (IGF-IR). A positive feedback loop appears to exist between NPM-ALK and IGF-IR through which these two kinases interact to potentiate their effects. We have also found that a single mutation of the Tyr(644) or Tyr(664) residue of the C terminus of NPM-ALK to phenylalanine decreases significantly, but does not completely abolish, the association between NPM-ALK and IGF-IR. The purpose of this study was to determine whether the dual mutation of Tyr(644) and Tyr(664) abrogates the association and interactions between NPM-ALK and IGF-IR. We also examined the impact of this dual mutation on the oncogenic potential of NPM-ALK. Our results show that NPM-ALK(Y644,664F) completely lacks association with IGF-IR. Importantly, we found that the dual mutation of Tyr(644) and Tyr(664) diminishes the oncogenic effects of NPM-ALK, including its ability to induce anchorage-independent colony formation and to sustain cellular transformation, proliferation, and migration. Furthermore, the association between NPM-ALK and IGF-IR through Tyr(644) and Tyr(664) appears to contribute to maintaining the stability of NPM-ALK protein. Our results provide novel insights into the mechanisms by which NPM-ALK induces its oncogenic effects through interactions with IGF-IR in this aggressive lymphoma.

Something old, something new and something borrowed: emerging paradigm of insulin-like growth factor type 1 receptor (IGF-1R) signaling regulation

The insulin-like growth factor type 1 receptor (IGF-1R) plays a key role in the development and progression of cancer; however, therapeutics targeting it have had disappointing results in the clinic. As a receptor tyrosine kinase (RTK), IGF-1R is traditionally described as an ON/OFF system, with ligand stabilizing the ON state and exclusive kinase-dependent signaling activation. Newly added to the traditional model, ubiquitin-mediated receptor downregulation and degradation was originally described as a response to ligand/receptor interaction and thus inseparable from kinase signaling activation. Yet, the classical model has proven over-simplified and insufficient to explain experimental evidence accumulated over the last decade, including kinase-independent signaling, unbalanced signaling, or dissociation between signaling and receptor downregulation. Based on the recent findings that IGF-1R “borrows” components of G-protein coupled receptor (GPCR) signaling, including β-arrestins and G-protein-related kinases, we discuss the emerging paradigm for the IGF-1R as a functional RTK/GPCR hybrid, which integrates the kinase signaling with the IGF-1R canonical GPCR characteristics. The contradictions to the classical IGF-1R signaling concept as well as the design of anti-IGF-1R therapeutics treatment are considered in the light of this paradigm shift and we advocate recognition of IGF-1R as a valid target for cancer treatment.

Three are better than one: plasminogen receptors as cancer theranostic targets

Activation of plasminogen on the cell surface initiates a cascade of protease activity with important implications for several physiological and pathological events. In particular, components of the plasminogen system participate in tumor growth, invasion and metastasis. Plasminogen receptors are in fact expressed on the cell surface of most tumors, and their expression frequently correlates with cancer diagnosis, survival and prognosis. Notably, they can trigger multiple specific immune responses in cancer patients, highlighting their role as tumor-associated antigens. In this review, three of the most characterized plasminogen receptors involved in tumorigenesis, namely Annexin 2 (ANX2), Cytokeratin 8 (CK8) and alpha-Enolase (ENOA), are analyzed to ascertain an overall view of their role in the most common cancers. This analysis emphasizes the possibility of delineating new personalized therapeutic strategies to counteract tumor growth and metastasis by targeting plasminogen receptors, as well as their potential application as cancer predictors.

Aldosterone stimulates elastogenesis in cardiac fibroblasts via mineralocorticoid receptor-independent action involving the consecutive activation of Galpha13, c-Src, the insulin-like growth factor-I receptor, and phosphatidylinositol 3-kinase/Akt

We previously demonstrated that aldosterone, which stimulates collagen production through the mineralocorticoid receptor (MR)-dependent pathway, also induces elastogenesis via a parallel MR-independent mechanism involving insulin-like growth factor-I receptor (IGF-IR) signaling. The present study provides a more detailed explanation of this signaling pathway. Our data demonstrate that small interfering RNA-driven elimination of MR in cardiac fibroblasts does not inhibit aldosterone-induced IGF-IR phosphorylation and subsequent increase in elastin production. These results exclude the involvement of the MR in aldosterone-induced increases in elastin production. Results of further experiments aimed at identifying the upstream signaling component(s) that might be activated by aldosterone also eliminate the putative involvement of pertussis toxin-sensitive Galphai proteins, which have previously been shown to be responsible for some MR-independent effects of aldosterone. Instead, we found that small interfering RNA-dependent elimination of another heterotrimeric G protein, Galpha13, eliminates aldosterone-induced elastogenesis. We further demonstrate that aldosterone first engages Galpha13 and then promotes its transient interaction with c-Src, which constitutes a prerequisite step for aldosterone-dependent activation of the IGF-IR and propagation of consecutive downstream elastogenic signaling involving phosphatidylinositol 3-kinase/Akt. In summary, the data we present reveal new details of an MR-independent cellular signaling pathway through which aldosterone stimulates elastogenesis in human cardiac fibroblasts.

Rapamycin together with herceptin significantly increased anti-tumor efficacy compared to either alone in ErbB2 over expressing breast cancer cells

The objective of this study was to assess the anti-tumor efficacy of rapamycin alone or in combination with herceptin in breast cancer. A total of 20 human breast cancer lines were examined for expression of various receptor tyrosine kinases and activation of their down stream signaling molecules, as well as for their invasion and colony forming ability. The ErbB2 and PI3 kinase pathway inhibitors were tested for the inhibition on breast cancer cell growth and tumor development. Seven of the 20 lines displayed an elevated level of ErbB2, others had varying level of EGF, IGF-1 or insulin receptor. Over 30% of the lines also had constitutive activation of Akt and MAP kinase. The lines displayed a wide range of colony forming and invasion ability. The PI3 kinase pathway inhibitors LY294002 and rapamycin inhibited the colony forming ability of all of the lines with the ErbB2 overexpressing lines having a higher sensitivity. A similar trend was observed for inhibition of invasion by LY294002. Rapamycin alone and additively together with herceptin inhibited the breast cancer cell growth especially in ErbB2 overexpressing cells. Rapamycin and herceptin synergistically inhibited tumor growth and endpoint tumor load in a xenograft model using a MCF-7 subline and in a MMTV-ErbB2 transgenic model. Rapamycin and herceptin significantly reduced the level of cyclin D1 and D3 and increased the cleavage of caspase 3 suggesting an increased apoptosis. Our results suggest that rapamycin together with herceptin has an enhanced anti-cancer effect and could be developed as an improved therapeutic regimen for breast cancer.

Role of Annexin-II in GI cancers: interaction with gastrins/progastrins

The role of the gastrin peptide hormones (G17, G34) and their precursors (progastrins, PG; gly-extended gastrin, G-gly), in gastrointestinal (GI) cancers has been extensively reviewed in recent years [W. Rengifo-Cam, P. Singh, Role of progastrins and gastrins and their receptors in GI and pancreatic cancers: targets for treatment, Curr. Pharm. Des. 10 (19) (2004) 2345-2358; M. Dufresne, C. Seva, D. Fourmy, Cholecystokinin and gastrin receptors, Physiol. Rev. 86 (3) (2006) 805-847; A. Ferrand, T.C. Wang, Gastrin and cancer: a review, Cancer Lett. 238 (1) (2006) 15-29]. A possible important role of progastrin peptides in colon carcinogenesis has become evident from experiments with transgenic mouse models [W. Rengifo-Cam, P. Singh, (2004); A. Ferrand, T.C. Wang, (2006)]. It is now known that growth stimulatory and co-carcinogenic effects of gastrin/PG peptides are mediated by both proliferative and anti-apoptotic effects of the peptides on target cells [H. Wu, G.N. Rao, B. Dai, P. Singh, Autocrine gastrins in colon cancer cells Up-regulate cytochrome c oxidase Vb and down-regulate efflux of cytochrome c and activation of caspase-3, J. Biol. Chem. 275 (42) (2000) 32491-32498; H. Wu, A. Owlia, P. Singh, Precursor peptide progastrin(1-80) reduces apoptosis of intestinal epithelial cells and upregulates cytochrome c oxidase Vb levels and synthesis of ATP, Am. J. Physiol. Gastrointest. Liver Physiol. 285 (6) (2003) G1097-G1110]. Several receptor subtypes have been described that mediate growth effects of gastrin peptides [W. Rengifo-Cam, P. Singh (2004); M. Dufresne, C. Seva, D. Fourmy, (2006)]. Recently, we identified Annexin II as a high affinity binding protein for gastrin/PG peptides [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798]. Importantly, the expression of Annexin II was required for mediating growth stimulatory effects of gastrin and PG peptides on intestinal epithelial and colon cancer cells [P. Singh, H. Wu, C. Clark, A. Owlia, Annexin II binds progastrin and gastrin-like peptides, and mediates growth factor effects of autocrine and exogenous gastrins on colon cancer and intestinal epithelial cells, Oncogene (2006), doi:10.1038/sj.onc.1209798], suggesting that Annexin-II may represent the elusive novel receptor for gastrin/PG peptides. The importance of this finding in relation to the structure and function of Annexin-II, especially in GI cancers, is described below. Since this surprising finding represents a new front in our understanding of the mechanisms involved in mediating growth effects of gastrin/PG peptides in GI cancers, our current understanding of the role of Annexin-II in proliferation and metastasis of cancer cells is additionally reviewed.

The role of the growth hormone/insulin-like growth factor axis in tumor growth and progression: Lessons from animal models

Over the past two decades it has become widely appreciated that a relationship exists between the insulin-like growth factors (IGFs) and cancer. Many cancers have been shown to overexpress the IGF-I receptor and produce the ligands (IGF-I or IGF-II) and some combinations of the six IGF-binding proteins. With the recent demonstration by epidemiological studies that an elevated serum IGF-I level is associated with an increased relative risk of developing a number of epithelial cancers, interest has been sparked in this area of research with the possibility of targeting the IGF-I receptor in cancer treatment protocols. This review highlights many of the most relevant studies in this exciting area of research, focusing in particular on lessons learned from animal models of cancer.

Caveolae-associated signalling in smooth muscle

Caveolae are flask-shaped invaginations in the membrane that depend on the contents of cholesterol and on the structural protein caveolin. The organisation of caveolae in parallel strands between dense bands in smooth muscle is arguably unique. It is increasingly recognised, bolstered in large part by recent studies in caveolae deficient animals, that caveolae sequester and regulate a variety of signalling intermediaries. The role of caveolae in smooth muscle signal transduction, as inferred from studies on transgenic animals and in vitro approaches, is the topic of the current review. Both G-protein coupled receptors and tyrosine kinase receptors are believed to cluster in caveolae, and the exciting possibility that caveolae provide a platform for interactions between the sarcoplasmic reticulum and plasmalemmal ion channels is emerging. Moreover, messengers involved in Ca2+ sensitization of myosin phosphorylation and contraction may depend on caveolae or caveolin. Caveolae thus appear to constitute an important signalling domain that plays a role not only in regulation of smooth muscle tone, but also in proliferation, such as seen in neointima formation and atherosclerosis.

Different methods of membrane domains isolation result in similar 2-D distribution patterns of membrane domain proteins

Membrane domains are highly specialized parts of the cell plasma membrane, carrying on and augmenting the incoming signals. To study their structural and functional properties, it is crucial to find the least damaging mode of their isolation. Using two different cell lines, epithelial HEK cells (clone E2M11) and S49 lymphoma cells, three methods of membrane domain isolation (i.e., detergent extraction, alkaline treatment, and "drastic" homogenization) were tested for similarity and reproducibility by 2-D electrophoresis. Our data show that the protein composition of membrane domains obtained by different isolation methods is similar and that approximately 60% of the spots are present in all membrane domain preparations. Furthermore, the same degree of similarity of 2-D profiles of the most intensively silver stained spots found in membrane domains of the two cell lines derived from different tissues suggests that the composition of a large part of membrane domains proteins is conservative. We suggest that these proteins may either be involved in the organization of membrane domain structure or represent the conservative component of signal transduction machinery.

Matrix-independent activation of phosphatidylinositol 3-kinase, Stat3, and cyclin A-associated Cdk2 Is essential for anchorage-independent growth of v-Ros-transformed chicken embryo fibroblasts

The question remains open whether the signaling pathways shown to be important for growth and transformation in adherent cultures proceed similarly and play similar roles for cells grown under anchorage-independent conditions. Chicken embryo fibroblasts (CEF) infected with the avian sarcoma virus UR2, encoding the oncogenic receptor protein-tyrosine kinase (RPTK) v-Ros, or with two of its transformation-impaired mutants were grown in nonadherent conditions in methylcellulose (MC)-containing medium, and the signaling functions essential for Ros-induced anchorage-independent growth were analyzed. We found that the overall tyrosine phosphorylation of cellular proteins in CEF transformed by v-Ros or by two oncogenic nonreceptor protein-tyrosine kinases (PTKs), v-Src and v-Yes, was dramatically reduced in nonadherent conditions compared with that in adherent conditions, indicating that cell adhesion to the extracellular matrix plays an important role in efficient substrate phosphorylation by these constitutively activated PTKs. The UR2 transformation-defective mutants were differentially impaired compared with UR2 in the activation of phosphatidylinositol 3-kinase (PI 3-kinase) and Stat3 in nonadherent conditions. Consistently, the constitutively activated mutants of PI 3-kinase and Stat3 rescued the ability of the UR2 mutants to promote anchorage-independent growth. Conversely, dominant negative mutants of PI 3-kinase and Stat3 inhibited UR2-induced anchorage-independent growth. UR2-infected CEF grown in nonadherent conditions displayed faster cell cycle progression than the control or the UR2 mutant-infected cells, and this appeared to correlate with a PI 3-kinase-dependent increase in cyclin A-associated Cdk2 activity. Treatment of UR2-infected cells with Cdk2 inhibitors led to the loss of the anchorage-independent growth-promoting activity of UR2. In conclusion, we have adopted an experimental system enabling us to study the signaling pathways in cells grown under anchorage-independent conditions and have identified matrix-independent activation of PI 3-kinase and Stat3 signaling functions, as well as the PI 3-kinase-dependent increase of cyclin A-associated Cdk2 kinase activity, to be critical for the Ros-PTK-induced anchorage-independent growth.

Secretion of Annexin II via activation of insulin receptor and insulin-like growth factor receptor

Annexin II is secreted into the extracellular environment, where, via interactions with specific proteases and extracellular matrix proteins, it participates in plasminogen activation, cell adhesion, and tumor metastasis and invasion. However, mechanisms regulating annexin II transport across the cellular membrane are unknown. In this study, we used coimmunoprecipitation to show that Annexin-II was bound to insulin and insulin-like growth factor-1 (IGF-1) receptors in PC12 cells and NIH-3T3 cells overexpressing insulin (NIH-3T3(IR)) or IGF-1 receptor (NIH-3T3(IGF-1R)). Stimulation of insulin and IGF-1 receptors by insulin caused a temporary dissociation of annexin II from these receptors, which was accompanied by an increased amount of extracellular annexin II detected in the media of PC12, NIH-3T3(IR), and NIH-3T3(IGF-1R) cells but not in that of untransfected NIH-3T3 cells. Activation of a different growth factor receptor, the platelet-derived growth factor receptor, did not produce such results. Tyrphostin AG1024, a tyrosine kinase inhibitor of insulin and IGF-1 receptor, was shown to inhibit annexin II secretion along with reduced receptor phosphorylation. Inhibitors of a few downstream signaling enzymes including phosphatidylinositol 3-kinase, pp60c-Src, and protein kinase C had no effect on insulin-induced annexin II secretion, suggesting a possible direct link between receptor activation and annexin II secretion. Immunocytochemistry revealed that insulin also induced transport of the membrane-bound form of annexin II to the outside layer of the cell membrane and appeared to promote cell aggregation. These results suggest that the insulin receptor and its signaling pathways may participate in molecular mechanisms mediating annexin II secretion.

KD, Toone EJ. Towards high affinity carbohydrate-binding proteins: Directed evolution of murine galectin-3

Towards a better understanding of the molecular basis of affinity, a directed evolution of murine galectin-3 (G3) was initiated to produce mutants with improved affinity for lactose and N-acetyllactosamine relative to the wild-type protein. A series of N-terminal truncations were developed to facilitate incorporation of the 35 kDa protein into a phage-display construct. Analysis of the various assemblies revealed that all such deletions produced protein unsuitable for use in directed evolution studies. Following fusion of the full-length galectin to p3 of filamentous phage, three libraries were constructed and biopanned for increased affinity for lactose. The first two libraries, of 1 × 105and 1 × 106members, respectively, were assembled through a combination of error-prone PCR and DNA shuffling. A third library was constructed using a modified staggered extension protocol (StEP), but contained only 10 members. Mutants were also engineered site-specifically to test the role of key residues in or near the binding pocket. Analysis of the mutants by ITC identified one mutation (R158G) that produces a twofold increase in affinity for lactose and another that results in a sixfold increase in affinity for N-acetyllactosamine. Solid-phase binding analysis of phage for nonexpressing proteins indicated that two other mutants demonstrated increased binding to beta-methyllactose relative to the wild-type protein. Together these studies validate the evolutionary approach and set the stage for the development of novel carbohydrate-binding proteins.Key words: phage display, directed evolution, galectin, thermodynamics, carbohydrates.

Zebrafish insulin-like growth factor-I receptor: molecular cloning and developmental expression

The biological actions of the insulin-like growth factors (IGFs) are mediated primarily by the IGF-I receptor (IGF-IR), and the IGF family has been highly conserved throughout vertebrate evolution. In this study we report the isolation of a 3 kb cDNA clone for the zebrafish IGF-IR that includes the complete 3' untranslated region and polyA tail and mapping of the receptor gene to zebrafish linkage group 7. The open reading frame deduced from the cDNA sequence encompasses the juxtamembrane and protein tyrosine kinase portions of the receptor, and is 70 and 67% identical to the corresponding regions of the IGF-IRs of the turbot and Xenopus, respectively. By RT-PCR, zebrafish IGF-IR expression was detected from early blastula to early larval stages of development. Using whole mount in situ hybridization, IGF-IR expression was detected after gastrulation. Expression was evident in most tissues but was particularly evident in the tail, in eye and ear primordia and in the brain.

Control of the nuclear-cytoplasmic partitioning of annexin II by a nuclear export signal and by p11 binding

This study investigated mechanisms controlling the nuclear-cytoplasmic partitioning of annexin II (AnxII). AnxII and its ligand, p11, were localized by immunofluorescence to the cytoplasmic compartment of U1242MG cells, with minimal AnxII or p11 detected within nuclei. Similarly, GFP-AnxII and GFP-p11 chimeras localized to the endogenous proteins. Likewise, GFP-AnxII(1-22) was excluded from nuclei, whereas GFP-AnxII(23-338) and GFP alone were distributed throughout the cells. Immunoprecipitation and biochemical studies showed that GFP-AnxII did not form heteromeric complexes with endogenous p11 and AnxII. Thus, the AnxII N-tail is necessary and sufficient to cause nuclear exclusion of the GFP fusion protein but this does not involve p11 binding. A nuclear export signal consensus sequence was found in the AnxII 3-12 region. The consensus mutant GFP-AnxII(L10A/L12A) confirmed that these residues are necessary for nuclear exclusion. The nuclear exclusion of GFP-AnxII(1-22) was temperature-dependent and reversible, and the nuclear export inhibitor leptomycin B (LmB) caused GFP-AnxII or overexpressed AnxII monomer to accumulate in nuclei. Therefore, AnxII monomer can enter the nucleus and is actively exported. However, LmB had little effect on the localization of AnxII/p11 complex in U1242MG cells, indicating that the complex is sequestered in the cytoplasm. By contrast, LmB treatment of v-src-transformed fibroblasts caused endogenous AnxII to accumulate in nuclei. The LmB-induced nuclear accumulation of AnxII was accelerated by pervanadate and inhibited by genistein, suggesting that phosphorylation promotes nuclear entry of AnxII. Thus, nuclear exclusion of AnxII results from nuclear export of the monomer and sequestration of AnxII/p11 complex, and may be modulated by phosphorylation.

Characterization of insulin-like growth factor I (IGF-I) receptor mutants for their effects on IGF-I- and interleukin 4-mediated DNA synthesis of 32D cells

Recently we demonstrated that overexpression of the wild type insulin-like growth factor I receptor (IGF-IRWT) in 32D myeloid progenitor cells led to cell proliferation in response to interleukin 4 (IL-4) as well as insulin-like growth factor I (IGF-I) in the absence of insulin receptor substrate expression (Soon, L., Flechner, L., Gutkind, J. S., Wang, L. H., Baserga, R., Pierce, J. H., and Li, W. (1999) Mol. Cell. Biol. 19, 3816-3828). To understand the structural importance of insulin-like growth factor I receptor (IGF-IR) in mediating IL-4- and IGF-I-induced DNA synthesis, we transfected various mutants of IGF-IR to 32D cells. Our results show that most mutants, including Y1250F, Y1251F, Y1250F/Y1251F, S1280A/S1281A/S1282A/S1283A, Y1316F, and 1245d, still retained mitogenic response toward IGF-I or IL-4. However, the Y950F, Y1131F, and Y1135F mutants were not able to respond to either ligand. The H1293F/K1294R and 1293d mutants reduced response toward IGF-I but not to IL-4. Phosphorylation of Shc was greatly reduced in those three mutants that lost mitogenic response. The MAPK activity was much lower in Y1131F and Y1135F mutants, indicating the importance of the Shc/MAPK pathway in IGF-I-induced mitogenesis. Importantly, the synergistic effect of these two factors on DNA synthesis was not affected in cells expressing most of the mutants, even in those three that had lower mitogenic response toward a single ligand. These results suggest that an unidentified pathway(s) may be induced upon co-addition of IGF-I and IL-4 that sustains the intact mitogenesis.

Differential requirements of the MAP kinase and PI3 kinase signaling pathways in Src- versus insulin and IGF-1 receptors-induced growth and transformation of rat intestinal epithelial cells

There have been few studies on the specific signaling pathways involved in the transformation of epithelial cells by oncogenic protein tyrosine kinases. Here we investigate the requirement of MAP (MAPK) and phosphatidylinositol 3- (PI3K) kinases in the transformation of rat intestinal epithelial (RIE) cells by oncogenic forms of insulin receptor (gag-IR), insulin-like growth factor-1 receptor (gag-IGFR), and v-Src. MAPK is not significantly activated in cells transformed by gag-IR and gag-IGFR but is activated in v-Src transformed cells. Treatment with PD98059, a MEK inhibitor, at concentrations where MAPK activity was reduced below the basal level showed that MAPK is partially required for the monolayer growth of parental and transformed RIE cells. However, MAPK is not essential for the focus forming ability of the three oncogene-transformed cells. It is also not necessary for the colony forming ability of gag-IR- and gag-IGFR-, but is partially required for v-Src-transformed cells. PI3K is significantly activated in all three oncogene transformed RIE cells. LY294002, a PI3K inhibitor, potently inhibited monolayer growth of all three oncogene-transformed cells. However, at concentrations of LY294002 where activated forms of Akt, a downstream component of the PI3K pathway, were undetectable, colony and focus forming abilities of the v-Src-RIE cells were only slightly affected whereas those of gag-IR/IGFR-RIE cells were greatly inhibited. These results were confirmed using a different pharmacological inhibitor, wortmannin, and a dominant negative form of PI3K, Ap85. Similarly, rapamycin, known to inhibit p70S6 kinase, a downstream component of the PI3K-Akt pathway, also inhibited gag-IR/IGFR-induced, but not v-Src-induced, focus and colony formation. We conclude that the MAPK and PI3K signaling pathways are differentially required for transformation of RIE cells by oncogenic IR and IGFR versus Src and the pattern of requirements is different from that of fibroblast transformation.

Mechanism of action in thalidomide teratogenesis

In this commentary, we describe a model to explain the mechanism of the embryopathy of thalidomide. We propose that thalidomide affects the following pathway during development: insulin-like growth factor I (IGF-I) and fibroblast growth factor 2 (FGF-2) stimulation of the transcription of alphav and beta3 integrin subunit genes. The resulting alphavbeta3 integrin dimer stimulates angiogenesis in the developing limb bud, which promotes outgrowth of the bud. The promoters of the IGF-I and FGF-2 genes, the genes for their binding proteins and receptors, as well as the alphav and beta3 genes, lack typical TATA boxes, but instead contain multiple GC boxes (GGGCGG). Thalidomide, or a breakdown product of thalidomide, specifically binds to these GC promoter sites, decreasing transcription efficiency of the associated genes. A cumulative decrease interferes with normal angiogenesis, which results in truncation of the limb. Intercalation into G-rich promoter regions of DNA may explain why certain thalidomide analogs are not teratogenic while retaining their anti-tumor necrosis factor-alpha (TNF-alpha) activity, and suggests that we look elsewhere to explain the action of thalidomide on TNF-alpha. On the other hand, the anti-cancer action of thalidomide may be based on its antiangiogenic action, resulting from specific DNA intercalation. The tissue specificity of thalidomide and its effect against only certain neoplasias may be explained by the fact that various developing tissues and neoplasias depend on different angiogenesis or vasculogenesis pathways, only some of which are thalidomide-sensitive.

Role of ERK and JNK pathways in regulating cell motility and matrix metalloproteinase 9 production in growth factor-stimulated human epidermal keratinocytes

Invasion is an essential cellular response that plays an important role in a number of physiological and pathological processes. Matrix metalloproteinase (MMP) production and cell movement are diverse cellular responses integral to the process of invasion. The complexity of the invasive process suggests the necessity of coordinate activation of more than one signaling pathway in order to activate specific factors responsible for regulating these cellular responses. In this report, we demonstrate that cell movement and MMP-9 production are both directly dependent on the activation of endogenous ERK signaling in hepatocyte growth factor (HGF)-or epidermal growth factor (EGF)-stimulated human epidermal keratinocytes. The kinetic profiles of endogenous MEK and ERK activity suggest that prolonged activation of these signal transducers is an underlying mechanism involved in stimulating cell motility and MMP-9 production. In support of this finding, a transient MEK/ERK signal elicited by keratinocyte growth factor (KGF) or insulin-like growth factor-1 (IGF-1) fails to stimulate these invasion-related responses. Specific inhibition of MEK leads to suppression of ERK activation, marked reduction in steady-state levels of c-Fos, and inhibition of cell movement and MMP-9 production. This occurs despite continued activation of JNK and c-Jun signaling in the presence of MEK-specific inhibition. In contrast, when JNK activity is specifically inhibited in HGF-stimulated cells, AP-1 activity is suppressed but cell motility is not affected. This evidence suggests that while ERK and JNK activity are necessary for AP-1 activation, ERK but not JNK is sufficient in stimulating cell motility.

Insulin-like growth factor I synergizes with interleukin 4 for hematopoietic cell proliferation independent of insulin receptor substrate expression

In the present study, we investigated the potential role of insulin-like growth factor I (IGF-I) receptor (IGF-IR) in cell proliferation by overexpressing it in 32D myeloid progenitor cells. The overexpression of IGF-IR caused the transfectants to proliferate in response to IGF-I in the absence of insulin receptor substrate (IRS) expression. The activation of overexpressed wild-type IGF-IR, but not that of an ATP-binding mutant of IGF-IR, resulted in the increased tyrosine phosphorylation of several intracellular proteins, including SHC, Src homology 2-containing inositol-5-phosphatase, protein kinase C-delta, and Erk2. Grb2 association with SHC and mitogen-activated protein kinase (MAPK) activity was also enhanced in response to IGF-I stimulation. Interestingly, the stimulation of the IGF-IR transfectants with interleukin 4 (IL-4) also resulted in strong mitogenesis independent of IRS expression. Moreover, IGF-I and/or IL-4 induced long-term cell growth of the IGF-IR transfectants. IL-4 was able to synergize with IGF-I for DNA synthesis, even in the parental 32D cells and a pro-B-cell line, Baf3, indicating the physiological importance of the two growth factors in hematopoietic cell proliferation. IL-4 stimulation of the IGF-IR transfectants resulted in enhanced tyrosine phosphorylation of SHC, Erk2, and signal transducer and activator of transcription 6 (STAT6) proteins. Both IL-4 and IGF-I were able to induce c-myc early response gene expression, and this expression was maximal in the presence of both factors. Finally, we demonstrated that a MAPK kinase inhibitor was able to suppress mitogenesis of the IGF-IR transfectants in response to IGF-I and/or IL-4. Together, our results suggest that IL-4 synergizes with IGF-I for hematopoietic cell proliferation, likely through cross talk between SHC/Grb2/MAPK and STAT6 pathways and through c-myc gene up-regulation.

Protein kinase C-delta is an important signaling molecule in insulin-like growth factor I receptor-mediated cell transformation

To investigate the potential role of protein kinase C-delta (PKC-delta) in insulin-like growth factor I receptor (IGF-IR)-mediated cell transformation, an oncogenic gag-IGF-IR beta-fusion receptor lacking the entire extracellular domain, which was designated NM1, and a full-length IGF-IR were coexpressed with either wild-type PKC-delta (PKC-deltaWT) or an ATP-binding mutant of PKC-delta (PKC-deltaK376R) in NIH 3T3 fibroblasts. While overexpression of PKC-deltaWT did not affect NM1- and IGF-IR-induced focus and colony formation of NIH 3T3 cells, expression of PKC-deltaK376R severely impaired these events. In contrast, NM1-mediated cell growth in monolayer was not affected by coexpressing PKC-deltaK376R. PKC-deltaWT and PKC-deltaK376R were constitutively phosphorylated on a tyrosine residue(s) in the NM1- and IGF-IR-expressing cells and were associated with them in an IGF-I-independent manner. Activated IGF-IR was able to phosphorylate purified PKC-delta in vitro and stimulated its kinase activity. Furthermore, the level of endogenous PKC-delta protein was up-regulated through transcriptional activation in response to long-term IGF-IR activation. Taken together, our results demonstrate that PKC-delta plays an important role in IGF-IR-mediated cell transformation, probably via association of the receptor with PKC-delta and its activation through protein up-regulation and tyrosine phosphorylation. Competition with endogenous PKC-delta for NM1 and IGF-IR association by PKC-deltaK376R is probably an important mechanism underlying the PKC-deltaK376R-mediated inhibition of cell transformation by NM1 and IGF-IR.

Structure and function of the insulin-like growth factor I receptor

Insulin-like growth factors I and II (IGF-I, IGF-II) were originally identified as potent mitogens and as the mediators of growth hormone action. Besides being mitogenic, however, these polypeptide growth factors play a crucial role in cell survival, and contribute to transformation and to maintenance of the malignant phenotype. Here we will discuss signaling by the IGFs, focusing specifically on the structure and function of the IGF-I receptor and the domains of this receptor responsible for distinct IGF functions: mitogenesis, transformation, and protection from apoptosis. We will also compare the structural domains of the related but functionally distinct receptor for insulin.

Mutations of Ros differentially effecting signal transduction pathways leading to cell growth versus transformation

The signaling functions of the oncogenic protein-tyrosine kinase v-Ros were studied by systematically mutating the tyrosine residues in its cytoplasmic domain. The carboxyl mutation of Tyr-564 produces the most pronounced inhibitory effect on v-Ros autophosphorylation and interaction with phospholipase Cgamma. A cluster of 3 tyrosine residues, Tyr-414, Tyr-418, and Tyr-419, within the PTK domain of v-Ros plays an important role in modulating its kinase activity. The mutant F419 and the mutant DI, deleting 6-amino acids near the catalytic loop, retain wild type protein tyrosine kinase and mitogenic activities, but have dramatically reduced oncogenicity. Both mutant proteins are able to phosphorylate or activate components in the Ras/microtubule-associated protein kinase signaling pathway. However, F419 mutant protein is unable to phosphorylate insulin receptor substrate 1 (IRS-1) or promote association of IRS-1 with phosphatidylinositol 3-kinase. This tyrosine residue in the context of the NDYY motif may define a novel recognition site for IRS-1. Both F419 and DI mutants display impaired ability to induce tyrosine phosphorylation of a series of cytoskeletal and cell-cell interacting proteins. Thus the F419 and DI mutations define v-Ros sequences important for cytoskeleton signaling, the impairment of which correlates with the reduced cell transforming ability.

Effect of dimerization on signal transduction and biological function of oncogenic Ros, insulin, and insulin-like growth factor I receptors

The avian sarcoma virus UR2 codes for an oncogenic Gag-Ros fusion protein-tyrosine kinase (PTK). We have previously derived two retroviruses, T6 and NM1, coding for oncogenic Gag-insulin receptor and Gag-insulin-like growth factor I receptor (IGFR) fusion proteins, respectively. The Gag-IGFR fusion protein dimerizes, whereas Gag-Ros does not. To identify sequences affecting dimerization and the effect of dimerization on signaling and biological functions, we generated recombinants exchanging the extracellular and transmembrane sequences among the three fusion receptors. The presence of multiple cysteines in the Gag sequence appears to preclude dimerization, since deletion of the 3' cysteine residue allows for dimerization. Most of the chimeric receptors retain high PTK activity and induce transformation regardless of their configuration on the cell surface. UT, a UR2/T6 chimera, retained mitogenic activity but has a markedly reduced transforming ability, while UN7, a UR2/NM1 recombinant, which also harbors Y950F and F951S mutations in IGFR, exhibits dramatic reductions in both activities. All of the fusion receptors can phosphorylate insulin receptor substrate 1 and activate PI 3-kinase. UT protein induces Shc phosphorylation, whereas UN7 protein does not, but both are unable to activate mitogen-activated protein kinase. Our results show that overexpressed oncogenic Gag-fusion receptors do not require dimerization for their signaling and transforming functions and that the extracellular and transmembrane sequences of a receptor PTK can affect its specific substrate interactions.