Differentiation and malignant transformation: two roads diverged in a wood

Long noncoding RNA CCAT2 reduces chemosensitivity to 5-fluorouracil in breast cancer cells by activating the mTOR axis

Breast cancer (BC) is the most prevalent cancer in women and the second leading cause for cancer‐related death in women. LncRNA CCAT2 is involved in BC cell drug sensitivity. Drug resistance of BC cells after chemotherapy is the main obstacle to therapeutic effects. This study explored whether BC cell drug sensitivity to 5‐Fu was related to lncRNA CCAT2‐regulated mTOR pathway. Normal breast tissues and BC tissues before/after neoadjuvant chemotherapy were collected, and CCAT2 expression was detected by RT‐qPCR. Correlation between CCATA2 expression and neoadjuvant chemotherapy efficacy was analysed using the Kendall's tau‐b correlation analysis. Normal breast epithelial cells and BC cell lines were cultured. BC cell lines were treated with 5‐Fu, and CCAT2 mRNA level in cells was detected. The 5‐Fu‐resistant MCF‐7/5‐Fu and MDA‐MB‐231/5‐Fu cells were treated with CCAT2 overexpression/knockdown or CCI‐779 (the mTOR pathway inhibitor). The mTOR pathway levels were detected. Expression of apoptosis‐related factors was identified. A subcutaneous xenograft model was carried out. High CCAT2 expression was detected in BC tissues and BC drug‐resistant cells after neoadjuvant chemotherapy, and a negative link was revealed between CCAT2 expression and efficacy of neoadjuvant chemotherapy. p‐mTOR/mTOR in 5‐Fu‐resistant BC cells with inhibited CCAT2 was decreased, while CCAT2 overexpression activated the mTOR pathway. IC50 value, proliferation, cells in S phase increased and apoptosis reduced after CCAT2 overexpression. After si‐CCAT2 or CCI‐779 treatment, the growth rate of transplanted tumours was inhibited, while promoted after CCAT2 overexpression. CCAT2 may reduce BC cell chemosensitivity to 5‐Fu by activating the mTOR pathway.

Knockdown of lncRNA CCAT2 inhibits endometrial cancer cells growth and metastasis via sponging miR-216b

OBJECTIVE

Colon cancer-associated transcript 2 (CCAT2), a novel lncRNA has been reported as an oncogene in several cancers. This study was aimed to explore whether CCAT2 also exerted oncogenic roles in endometrial cancer cells.

MATERIALS AND METHODS

The expression of CCAT2 in 30 pairs of endometrial cancer and matched non-cancerous tissues were detected by qRT-PCR. Two endometrial cancer cell lines HEC-1-A and RL95-2 were used throughout this study. CCAT2 in cells was silenced by transfection with shRNA targeted CCAT2, then cell growth and metastasis were assessed by performing trypan blue staining, Transwell assay, and flow cytometry. Dual-luciferase reporter assay was used to detect the combination of miR-216b and CCAT2. Besides, the expression of miR-216b and Bcl-2 in cells were overexpressed or suppressed by transfection with their correspondingly mimic/vector or inhibitor/shRNA. qRT-PCR and western blot analysis were performed to detect the expression of Bcl-2 and main factors in PTEN/PI3K/AKT and mTOR signaling pathways.

RESULTS

CCAT2 was highly expressed in endometrial cancer tissues when compared to non-cancerous endometrial tissues. Knockdown of CCAT2 inhibited HEC-1-A and RL95-2 cells viability, migration, invasion, but induced apoptosis. CCAT2 was an endogenous sponge by competing for miR-216b, and miR-216b suppression alleviated CCAT2 silence-diminished cell growth and metastasis. miR-216b negatively regulated Bcl-2 and Bcl-2 could further active PTEN/PI3K/AKT and mTOR signaling pathways.

CONCLUSIONS

To conclude, these results demonstrated lncRNA CCAT2 was highly expressed in endometrial cancer tissues. Knockdown of CCAT2 inhibited cell growth and metastasis of endometrial cancer cells by sponging miR-216b.

Characterization of DNA variants in the human kinome in breast cancer

Kinases play a key role in cancer biology, and serve as potential clinically useful targets for designing cancer therapies. We examined nucleic acid variations in the human kinome and several known cancer-related genes in breast cancer. DNA was extracted from fine needle biopsies of 73 primary breast cancers and 19 metastatic lesions. Targeted sequencing of 518 kinases and 68 additional cancer related genes was performed using the SOLiD sequencing platform. We detected 1561 unique, non-synonymous variants in kinase genes in the 92 cases, and 74 unique variants in 43 kinases that were predicted to have major functional impact on the protein. Three kinase groups—CMGC, STE and TKL—showed greater mutational load in metastatic compared to primary cancer samples, however, after correction for multiple testing the difference was significant only for the TKL group (P = 0.04). We also observed that a higher proportion of histologic grade 1 and 2 cases had high functional impact variants in the SCYL2 gene compared with grade 3 cases. Our findings indicate that individual breast cancers harbor a substantial number of potentially functionally important nucleotide variations in kinase genes, most of which are present in unique combinations and include both somatic and germline functional variants.

Ligand-mediated endocytosis and trafficking of the insulin-like growth factor receptor I and insulin receptor modulate receptor function

The insulin-like growth factor system and its two major receptors, the IGF receptor I (IGF-IR) and IR, plays a central role in a variety of physiological cellular processes including growth, differentiation, motility, and glucose homeostasis. The IGF-IR is also essential for tumorigenesis through its capacity to protect cancer cells from apoptosis. The IR is expressed in two isoforms: the IR isoform A (IR-A) and isoform B (IR-B). While the role of the IR-B in the regulation of metabolic effects has been known for several years, more recent evidence suggests that the IR, and in particular the IR-A, may be involved in the pathogenesis of cancer. Ligand-mediated endocytosis of tyrosine-kinases receptors plays a critical role in modulating the duration and intensity of receptors action but while the signaling pathways induced by the IGF-IR and IR are quite characterized, very little is still known about the mechanisms and proteins that regulate ligand-induced IGF-IR and IR endocytosis and trafficking. In addition, how these processes affect receptor downstream signaling has not been fully characterized. Here, we discuss the current understanding of the mechanisms and proteins regulating IGF-IR and IR endocytosis and sorting and their implications in modulating ligand-induced biological responses.

BRCA1 is expressed in uterine serous carcinoma (USC) and controls insulin-like growth factor I receptor (IGF-IR) gene expression in USC cell lines

OBJECTIVE

The insulin-like growth factor I receptor (IGF-IR) and BRCA1 affect cell growth and apoptosis. Little information is available about BRCA1 activity on the IGF signaling pathway. This study evaluated the effect of BRCA1 on IGF-IR expression.

METHODS

BRCA1 and IGF-IR immunohistochemistry on archival tissues (35 uterine serous carcinomas [USCs] and 17 metastases) were performed. USPC1 and USPC2 cell lines were transiently cotransfected with an IGF-IR promoter construct driving a luciferase reporter gene and a BRCA1 expression plasmid. Endogenous IGF-IR levels were evaluated by Western immunoblotting.

RESULTS

We found high BRCA1 and IGF-IR protein expression in primary and metastatic USC tumors. All samples were immunostained for BRCA1-71% strongly stained; and 33/35 (94%) were stained positive for IGF-IR-2 (6%) strongly stained. No difference in BRCA1 and IGF-IR staining intensity was noted between BRCA1/2 mutation carriers and noncarriers. Metastatic tumors stained more intensely for BRCA1 than did the primary tumor site (P = 0.041) and with borderline significance for IGF-IR (P = 0.069). BRCA1 and IGF-IR staining did not correlate to survival. BRCA1 expression led to 35% and 54% reduction in IGF-IR promoter activity in the USPC1 and USCP2 cell lines, respectively. Western immunoblotting showed a decline in phosphorylated IGF-IR and phosphorylated AKT in both transiently and stably transfected cells.

CONCLUSIONS

BRCA1 and IGF-IR are highly expressed in USC tumors. BRCA1 suppresses IGF-IR gene expression and activity. These findings suggest a possible biological link between the BRCA1 and the IGF-I signaling pathways in USC. The clinical implications of this association need to be explored.

Gefitinib resistance in HCC mahlavu cells: upregulation of CD133 expression, activation of IGF-1R signaling pathway, and enhancement of IGF-1R nuclear translocation

Hepatocellular carcinoma (HCC) is the major form of primary liver cancer which accounts for more than half million deaths annually worldwide. While the incidence of HCC is still on the rise, options of treatment are limited and the overall survival rate is poor. The acquisition of cancer drug resistance remains one of the key hurdles to successful treatment. Clearly, a thorough understanding of the underlying mechanisms is needed for new strategies to design novel treatments and/or to improve the current therapies. In the present study, we examined the expression of cancer stem cell (CSC) marker CD133, the activation of insulin-like growth factor 1 receptor (IGF-1R) signaling, and the nuclear translocation of IGF-1R in HCC Mahlavu cells under the treatment of gefitinib, a cancer drug that inhibits epidermal growth factor receptor (EGFR) pathway. Our results demonstrated that Mahlavu cells exhibited strong gefitinib resistance and the CD133 expression level was dramatically increased (from 3.88% to 32%) after drug treatment. In addition, the gefitinib treated cells displayed increased levels of phosphorylation in IGF-1R and Akt, indicating the intensified activation of this cancer-associated signaling pathway. Moreover, we revealed that IGF-1R underwent nuclear translocation in gefitinib treated cells using confocal microscopy. The IGF-1R nuclear translocation was enhanced under gefitinib treatment and appeared in a dose-dependent manner. Our findings suggest that increased IGF-1R nuclear translocation after gefitinib treatment may contribute to the drug resistance and IGF1-R activation, which might also associate with the upregulation of CD133 expression.

Proline-rich tyrosine kinase 2 (Pyk2) regulates IGF-I-induced cell motility and invasion of urothelial carcinoma cells

The insulin-like growth factor receptor I (IGF-IR) plays an essential role in transformation by promoting cell growth and protecting cancer cells from apoptosis. We have recently demonstrated that the IGF-IR is overexpressed in invasive bladder cancer tissues and promotes motility and invasion of urothelial carcinoma cells. These effects require IGF-I-induced Akt- and MAPK-dependent activation of paxillin. The latter co-localizes with focal adhesion kinases (FAK) at dynamic focal adhesions and is critical for promoting motility of urothelial cancer cells. FAK and its homolog Proline-rich tyrosine kinase 2 (Pyk2) modulate paxillin activation; however, their role in regulating IGF-IR-dependent signaling and motility in bladder cancer has not been established. In this study we demonstrate that FAK was not required for IGF-IR-dependent signaling and motility of invasive urothelial carcinoma cells. On the contrary, Pyk2, which was strongly activated by IGF-I, was critical for IGF-IR-dependent motility and invasion and regulated IGF-I-dependent activation of the Akt and MAPK pathways. Using immunofluorescence and AQUA analysis we further discovered that Pyk2 was overexpressed in bladder cancer tissues as compared to normal tissue controls. Significantly, in urothelial carcinoma tissues there was increased Pyk2 localization in the nuclei as compared to normal tissue controls. These results provide the first evidence of a specific Pyk2 activity in regulating IGF-IR-dependent motility and invasion of bladder cancer cells suggesting that Pyk2 and the IGF-IR may play a critical role in the invasive phenotype in urothelial neoplasia. In addition, Pyk2 and the IGF-IR may serve as novel biomarkers with diagnostic and prognostic significance in bladder cancer.

Decorin antagonizes IGF receptor I (IGF-IR) function by interfering with IGF-IR activity and attenuating downstream signaling

We have recently discovered that the insulin-like growth factor receptor I (IGF-IR) is up-regulated in human invasive bladder cancer and promotes migration and invasion of transformed urothelial cells. The proteoglycan decorin, a key component of the tumor stroma, can positively regulate the IGF-IR system in normal cells. However, there are no available data on the role of decorin in modulating IGF-IR activity in transformed cells or in tumor models. Here we show that the expression of decorin inversely correlated with IGF-IR expression in low and high grade bladder cancers (n = 20 each). Decorin bound with high affinity IGF-IR and IGF-I at distinct sites and negatively regulated IGF-IR activity in urothelial cancer cells. Nanomolar concentrations of decorin promoted down-regulation of IRS-1, one of the critical proteins of the IGF-IR pathway, and attenuated IGF-I-dependent activation of Akt and MAPK. This led to decorin-evoked inhibition of migration and invasion upon IGF-I stimulation. Notably, decorin did not cause down-regulation of the IGF-IR in bladder, breast, and squamous carcinoma cells. This indicates that decorin action on the IGF-IR differs from its known activity on other receptor tyrosine kinases such as the EGF receptor and Met. Our results provide a novel mechanism for decorin in negatively modulating both IGF-I and its receptor. Thus, decorin loss may contribute to increased IGF-IR activity in the progression of bladder cancer and perhaps other forms of cancer where IGF-IR plays a role.

The insulin-like growth factor receptor I promotes motility and invasion of bladder cancer cells through Akt- and mitogen-activated protein kinase-dependent activation of paxillin

The insulin-like growth factor receptor I (IGF-IR) plays an essential role in transformation by promoting cell growth and protecting cancer cells from apoptosis. Aberrant IGF-IR signaling is implicated in several types of tumors, including carcinomas of the lung, breast, prostate, pancreas, liver, and colon. However, the contribution of the IGF-IR to the development of the transformed phenotype in urothelial cells has not been clearly established. In this study we demonstrated that the IGF-IR is overexpressed in invasive bladder cancer tissues compared with nonmalignant controls. We have investigated the role of the IGF-IR in bladder cancer by using urothelial carcinoma-derived 5637 and T24 cells. Although activation of the IGF-IR did not appreciably affect their growth, it did promote migration and stimulate in vitro wound closure and invasion. These effects required the activation of the Akt and Mitogen-activated protein kinase (MAPK) pathways as well as IGF-I-induced Akt- and MAPK-dependent phosphorylation of paxillin, which relocated at dynamic focal adhesions and was necessary for promoting motility in bladder cancer cells. Our results provide the first evidence for a role of the IGF-IR in motility and invasion of bladder cancer cells and support the hypothesis that the IGF-IR may play a critical role in the establishment of the invasive phenotype in urothelial neoplasia. Thus, the IGF-IR may also serve as a novel biomarker for bladder cancer.

Nordihydroguaiaretic acid (NDGA), an inhibitor of the HER2 and IGF-1 receptor tyrosine kinases, blocks the growth of HER2-overexpressing human breast cancer cells

We have reported that nordihydroguaiaretic acid (NDGA) inhibits the tyrosine kinase activities of the IGF-1 receptor (IGF-1R) and the HER2 receptor in breast cancer cells. Herein, we studied the effects of NDGA on the growth of estrogen receptor (ER) positive MCF-7 cells engineered to overexpress HER2 (MCF-7/HER2-18). These cells are an in vitro model of HER2-driven, ER positive, tamoxifen resistant breast cancer. NDGA was equally effective at inhibiting the growth of both parental MCF-7 and MCF-7/HER2-18 cells. Half maximal effects for both cell lines were in the 10-15 microM range. The growth inhibitory effects of NDGA were associated with an S phase arrest in the cell cycle and the induction of apoptosis. NDGA inhibited both IGF-1R and HER2 kinase activities in these breast cancer cells. In contrast, Gefitinib, an epidermal growth factor receptor inhibitor but not an IGF-1R inhibitor, was more effective in MCF-7/HER2-18 cells than in the parental MCF-7 cells and IGF binding protein-3 (IGFBP-3) was more effective against MCF-7 cells compared to MCF-7/HER2-18. MCF-7/HER2-18 cells are known to be resistant to the effects of the estrogen receptor inhibitor, tamoxifen. Interestingly, NDGA not only inhibited the growth of MCF-7/HER2-18 on its own, but it also demonstrated additive growth inhibitory effects when combined with tamoxifen. These studies suggest that NDGA may have therapeutic benefits in HER2-positive, tamoxifen resistant, breast cancers in humans.

Growth-inhibitory effects of human anti-insulin-like growth factor-I receptor antibody (A12) in an orthotopic nude mouse model of anaplastic thyroid carcinoma

PURPOSE

The insulin-like growth factor-I receptor (IGF-IR) and its ligands have been implicated in the pathogenesis and progression of various cancers, including those arising in the thyroid gland. We therefore evaluated whether the IGF-IR could serve as a potential target for therapy of anaplastic thyroid carcinoma (ATC).

EXPERIMENTAL DESIGN

The expression and activation of the IGF-IR and some of its downstream signaling pathway components were evaluated in both human thyroid cancer specimens and thyroid cancer cell lines. The therapeutic potential of a humanized monoclonal antibody (A12) directed against IGF-IR was assessed in vitro and in vivo in an orthotopic model of ATC. Tumor volume and overall survival time were analyzed to evaluate the efficacy of A12 in vivo.

RESULTS

IGF-IR was overexpressed in 94% of the thyroid cancers. Blockade of IGF-IR with A12 was effective in attenuating IGF-IR signaling both in vitro and in vivo. However, the inhibitory effects of A12 on cell proliferation were cell line dependent, as those ATC cell lines that had detectable levels of pIGF-IR were more sensitive to A12 treatment. A12 was equally effective in vivo, where it brought approximately 57% (P = 0.041) inhibition in tumor volume. The concomitant use of A12 and irinotecan produced additive effects and resulted in a 93% (P < 0.001) reduction in tumor volume. Blocking IGF-IR blocked Akt phosphorylation and decreased proliferation and microvessel density but increased apoptosis within the tumor xenografts. Our results also highlighted a previously undefined IGF-IR-mediated antiangiogenic effect on tumor-associated endothelium in thyroid cancers.

CONCLUSION

Blocking the IGF-IR with A12 seems to be a potential avenue for treating patients with ATC by its direct antitumor effects and its effects on the tumor vasculature.

The insulin-like growth factor 1 receptor in cancer: old focus, new future

The importance of insulin-like growth factor 1 receptor (IGF-1R) signalling in malignant behaviour of tumour cells is well established. Currently, development of drugs targeting the IGF-1R as anticancer treatment is emerging. Several IGF-1R targeting strategies are being investigated in phases I and II clinical trials. Interactions of IGF-1R with insulin receptor, however, might complicate efficiency and tolerability of such drugs. This review describes mechanisms, recent developments and potential limitations of IGF-1R antibodies and tyrosine kinase inhibitors.

Functions and regulation of transforming growth factor-beta (TGF-β) in the prostate

The prostate is a highly androgen-dependent tissue that in humans exhibits marked susceptibility to carcinogenesis. The malignant epithelium generated from this tissue ultimately loses dependence on androgens despite retention or amplification of the androgen receptor. Accumulating evidence support that transforming growth factor-beta (TGF-beta) plays key roles in the control of androgen dependence and acquisition of resistance to such hormonal control. Although TGF-beta functions as a key tumour suppressor of the prostate, it can also promote malignant progression and metastasis of the advanced disease, through undefined mechanisms. In addition to giving an overview of the TGF-beta field as related to its function in prostate cancer, this Review focuses on novel findings that support the tumour suppressor function of TGF-beta is lost or altered by changes in the activity of the androgen receptor, insulin-like growth factor-I, Akt, and mTOR during malignant progression. Understanding the mechanisms of cross-talk between TGF-beta and such growth modulators has important implications for the rational therapeutics of prostate cancer.

JAK/STAT, Raf/MEK/ERK, PI3K/Akt and BCR-ABL in cell cycle progression and leukemogenesis

The roles of the JAK/STAT, Raf/MEK/ERK and PI3K/Akt signal transduction pathways and the BCR-ABL oncoprotein in leukemogenesis and their importance in the regulation of cell cycle progression and apoptosis are discussed in this review. These pathways have evolved regulatory proteins, which serve to limit their proliferative and antiapoptotic effects. Small molecular weight cell membrane-permeable drugs that target these pathways have been developed for leukemia therapy. One such example is imatinib mesylate, which targets the BCR-ABL kinase as well as a few structurally related kinases. This drug has proven to be effective in the treatment of CML patients. However, leukemic cells have evolved mechanisms to become resistant to this drug. A means to combat drug resistance is to target other prominent signaling components involved in the pathway or to inhibit BCR-ABL by other mechanisms. Treatment of imatinib-resistant leukemia cells with drugs that target Ras (farnysyl transferase inhibitors) or with the protein destabilizer geldanamycin has proven to be a means to inhibit the growth of resistant cells. This review will tie together three important signal transduction pathways involved in the regulation of hematopoietic cell growth and indicate how their expression is dysregulated by the BCR-ABL oncoprotein.

Insulin-like growth factor-I inhibits transcriptional responses of transforming growth factor-beta by phosphatidylinositol 3-kinase/Akt-dependent suppression of the activation of Smad3 but not Smad2

Insulin-like growth factor-I (IGF-I) and transforming growth factor-beta (TGF-beta) have been shown to be oncogenic and tumor suppressive, respectively, on prostate epithelial cells. Here we show that IGF-I inhibits the ability of TGF-beta to regulate expression of several genes in the non-tumorigenic rat prostatic epithelial line, NRP-152. In these cells, IGF-I also inhibits TGF-beta-induced transcriptional responses, as shown by several promoter reporter constructs, suggesting that IGF-I intercepts an early step in TGF-beta signaling. We show that IGF-I does not down-regulate TGF-beta receptor levels, as determined by both receptor cross-linking and Western blot analyses. However, Western blot analysis reveals that IGF-I selectively inhibits the TGF-beta-triggered activation Smad3 but not Smad2, while not altering expression of total Smads 2, 3, or 4. The phosphatidylinositol 3-kinase (PI3K) inhibitor, LY29004 reverses the ability of IGF-I to inhibit TGF-beta-induced transcriptional responses and the activation of Smad3, suggesting that the suppression of TGF-beta signaling by IGF-I is mediated through activation of PI3K. Moreover, we show that enforced expression of dominant-negative PI3K (DN-p85alpha) or phosphatidylinositol 3-phosphate-phosphatase, PTEN, also reverse the suppressive effect of IGF-I on TGF-beta-induced 3TP-luciferase reporter activity, whereas constitutively active PI3K (p110alphaCAAX) completely blocks TGF-beta-induced 3TP-luciferase reporter activity. Further transfection experiments including expression of constitutively active and dominant-negative Akt and rapamycin treatment suggest that suppression of TGF-beta signaling/Smad3 activation by IGF-I occurs downstream of Akt and through mammalian target of rapamycin activation. In summary, our data suggest that IGF-I inhibits TGF-beta transcriptional responses through selective suppression of Smad3 activation via a PI3K/Akt-dependent pathway.

Involvement of PI3K/Akt pathway in cell cycle progression, apoptosis, and neoplastic transformation: a target for cancer chemotherapy

The PI3K/Akt signal transduction cascade has been investigated extensively for its roles in oncogenic transformation. Initial studies implicated both PI3K and Akt in prevention of apoptosis. However, more recent evidence has also associated this pathway with regulation of cell cycle progression. Uncovering the signaling network spanning from extracellular environment to the nucleus should illuminate biochemical events contributing to malignant transformation. Here, we discuss PI3K/Akt-mediated signal transduction including its mechanisms of activation, signal transducing molecules, and effects on gene expression that contribute to tumorigenesis. Effects of PI3K/Akt signaling on important proteins controlling cellular proliferation are emphasized. These targets include cyclins, cyclin-dependent kinases, and cyclin-dependent kinase inhibitors. Furthermore, strategies used to inhibit the PI3K/Akt pathway are presented. The potential for cancer treatment with agents inhibiting this pathway is also addressed.

The IGF pathway regulates head formation by inhibiting Wnt signaling in Xenopus

The insulin-like growth factors (IGFs) are well known mitogens, both in vivo and in vitro, while functions in cellular differentiation have also been indicated. Here, we demonstrate a new role for the IGF pathway in regulating head formation in Xenopus embryos. Both IGF-1 and IGF-2, along with their receptor IGF-1R, are expressed early during embryogenesis, and the IGF-1R is present particularly in anterior and dorsal structures. Overexpression of IGF-1 leads to anterior expansion of head neural tissue as well as formation of ectopic eyes and cement gland, while IGF-1 receptor depletion using antisense morpholino oligonucleotides drastically reduces head structures. Furthermore, we demonstrate that IGF signaling exerts this effect by antagonizing the activity of the Wnt signal transduction pathway in the early embryo, at the level of beta-catenin. Thus, the IGF pathway is required for head formation during embryogenesis.

Regulation of insulin-like growth factor type I (IGF-I) receptor kinase activity by protein tyrosine phosphatase 1B (PTP-1B) and enhanced IGF-I-mediated suppression of apoptosis and motility in PTP-1B-deficient fibroblasts

The insulin-like growth factor type I (IGF-I) receptor (IGF-IR), activated by its ligands IGF-I and IGF-II, can initiate several signal transduction pathways that mediate suppression of apoptosis, proliferation, differentiation, and transformation. Here we investigated the regulation of IGF-IR activation and function by protein tyrosine phosphatase 1B (PTP-1B). Coexpression of PTP-1B with a beta-chain construct of the IGF-IR (betaWT) inhibited IGF-IR kinase activity in fission yeast Schizosaccharomyces pombe, in COS cells, and in IGF-IR-deficient fibroblasts. In both spontaneously immortalized and simian virus 40 T antigen-transformed embryonic fibroblast cell lines derived from PTP-1B knockout mice, IGF-I induced higher levels of IGF-IR autophosphorylation and kinase activity than were induced in PTP-1B-expressing control cells. PTP-1B-deficient cells exhibited enhanced IGF-I-mediated protection from apoptosis in response to serum withdrawal or etoposide killing, as well as enhanced plating efficiency and IGF-I-mediated motility. Reexpression of PTP-1B in spontaneously immortalized fibroblasts resulted in decreased IGF-IR and AKT activation, as well as decreased protection from apoptosis and decreased motility. These findings demonstrate that PTP-1B can regulate IGF-IR kinase activity and function and that loss of PTP-1B can enhance IGF-I-mediated cell survival, growth, and motility in transformed cells.

IGF-II induces rapid beta-catenin relocation to the nucleus during epithelium to mesenchyme transition

The epithelium to mesenchyme transition is thought to play a fundamental role during embryonic development and tumor progression. Loss of cell-cell adhesion and modification of both cell morphology and gene expression are the main events associated with this transition. There is a large amount of evidence suggesting that growth factors can initiate these events. Yet, the connection from growth factor induction to changes in cell adhesion and morphology is largely unknown. To elucidate this connection, we have investigated the action of IGF-II on E-cadherin/beta-catenin complex-mediated cell-cell adhesion and on beta-catenin/TCF-3 mediated gene expression. We can show that (1) IGF-II induces a rapid epithelium to mesenchymal transition; (2) IGF1R, the receptor for IGF-II, belongs to the same membrane complex as E-cadherin and beta-catenin; (3) IGF-II induces a redistribution of beta-catenin from the plasma membrane to the nucleus and an intracellular sequestration and degradation of E-cadherin; (4) IGF-II induces the transcription of beta-catenin/TCF-3 target genes. Based on the given case of IGF-II and E-cadherin/beta-catenin complex, this study reveals the backbone of a cascade connecting growth factor signaling with cell-cell adhesion during EMT.

The role of the insulin receptor substrate-1 in the differentiation of rat hippocampal neuronal cells

H19-7/IGF-IR cells are rat hippocampal cells expressing a human IGF-I receptor, which differentiate to a neuronal phenotype when stimulated by IGF-I at 39 degrees C. H19-7/IGF-IR cells have low levels of expression of insulin receptor substrate-l (IRS-1), a major substrate of the IGF-IR. IGF-I induces serine-phosphorylation and down-regulation of the endogenous IRS-1 upon differentiation of H19-7/IGF-IR cells. The profound influence of IRS-1 on differentiation of H19-7/IGF-IR cells was confirmed by transfecting these cells with a plasmid expressing mouse IRS-1. Over-expression of wild type IRS-1 in H19-7/IGF-IR cells abolishes IGF-I-induced differentiation at 39 degrees C. A mutant of IRS-1 lacking the PTB domain loses the ability to inhibit the differentiation program. H19-7/IGF-IR/IRS-1 cells at 39 degrees C show a stronger and prolonged activation of Akt, when compared to H19-7/IGF-IR cells. The role of Akt in the inhibition of the differentiation program was confirmed by using the inhibitor of Class I PI3 kinases LY29400, which restores IGF-I-induced differentiation of H19-7/IGF-IR/IRS-1 cells. H19-7/IGF-IR/IRS-1 cells show a strong reduction in MAP kinases signaling, which is related to the superactivation of Akt. This was confirmed by expressing in H19-7/IGF-IR cells a constitutively active Akt, which inhibited MAP kinases activation in these cells. These experiments confirm the importance of MAPK in the mechanism of IGF-I-mediated differentiation of H19-7/IGF-IR cells

Regulation of Id gene expression by type I insulin-like growth factor: roles of Stat3 and the tyrosine 950 residue of the receptor

Id proteins are known to play important roles in the proliferation and differentiation of many cell types. The type 1 insulin-like growth factor receptor (IGF-IR), activated by its ligand, induces the differentiation of 32D IGF-IR cells, a murine hematopoietic cell line, expressing a human IGF-IR. Expression in 32D IGF-IR cells of a dominant negative mutant of Stat3 (DNStat3) inhibits IGF-I-mediated differentiation. DNStat3 causes a dramatic increase in Id2 gene expression. This increase, however, is IGF-I dependent and is abrogated by a mutation at tyrosine 950 of the IGF-IR. These results indicate that in 32D cells, the IGF-IR regulates the expression of the Id2 gene and that this regulation is modulated by both positive and negative signals. Our results also suggest that in this model, Id2 proteins influence the differentiation program of cells but are not sufficient for the full stimulation of their proliferation program.

IGF-I receptor signalling in transformation and differentiation

The type 1 insulin-like growth factor receptor (IGF-IR) sends several signals, some of which are contradictory. When the concentrations of insulin receptor substrate 1 (IRS-1), a major substrate of the IGF-IR, are high, the signal is mitogenic, anti-apoptotic, and can even cause malignant transformation. However, in the absence of IRS-1, the IGF-IR sends a differentiation signal, which leads to granulocytic differentiation in haemopoietic cells. The mitogenic signal of the IGF-IR/IRS-1 combination depends largely, but not exclusively, on the activation of the phosphatidylinositol-3 kinase (PI3K).

Regulation of Id2 gene expression by the insulin-like growth factor I receptor requires signaling by phosphatidylinositol 3-kinase

The Id proteins play an important role in proliferation, differentiation, and tumor development. We report here that Id gene expression can be regulated by the insulin-like growth factor I receptor (IGF-IR), a receptor that also participates in the regulation of cellular proliferation and differentiation. Specifically, we found that the IGF-IR activated by its ligand was a strong inducer of Id2 gene expression in 32D murine hemopoietic cells. This activation was not simply the result of cellular proliferation, as Id2 gene expression was higher in 32D cells stimulated by IGF-I than in cells exponentially growing in interleukin-3. The up-regulation of Id2 gene expression was largely dependent on the presence of insulin receptor substrate-1, a major substrate of the IGF-IR and a potent activator of the phosphatidylinositol 3-kinase (PI3K) pathway. The role of PI3K activity in the up-regulation of Id2 gene expression by the IGF-IR was confirmed by different methods and in different cell types. In 32D cells, the up-regulation of Id2 gene expression by the PI3K pathway correlated with interleukin-3 independence and inhibition of differentiation.