IGF-I Receptor Gene Expression Research Articles

FRI293 Phoenixin As A Novel Autocrine/Paracrine Factor Mediating Prolactin Regulation By Functional Interaction Of LH And IGF-I/-II In Carp Pituitary Cells

Abstract Disclosure: C. Ye: None. X. Qin: None. M. He: None. A.O. Wong: None. Phoenixin (PNX), a novel peptide identified by bioinformatics, is known to have pleiotropic functions mediated by its receptor GPR173. At present, very little is known for PNX regulation and the intracellular signaling for PNX expression is still unclear. Recently, PNX and GPR173 were cloned in grass carp and found to be co-expressed in carp lactotrophs. In carp pituitary cells, PNX was also confirmed to be a novel autocrine/paracrine factor maintaining/stimulating prolactin (PRL) synthesis & secretion. To unveil the functional role of PNX in PRL regulation, a systematic screening of >40 neuroendocrine factors/local growth factors was conducted in the same cell model to look for regulators with modulatory functions for both PNX and PRL in carp pituitary. Based on our study, IGF-I & -II were shown to elevate PNX mRNA level with parallel rise in PRL gene expression in carp pituitary cells whereas the opposite was true for the functional agonist of LH, namely hCG. In parallel experiment, PRL mRNA expression induced by IGF-I was negated by removing endogenous PNX using immunoneutralization with PNX antiserum. Besides, hCG inhibition on PNX & PRL gene expression could be mimicked by parallel treatment of LH but not FSH, whereas removal of endogenous LH by LH antiserum immunoneutralization could lead to the opposite effects. Of note, hCG co-treatment not only attenuated the PNX and PRL responses induced by IGF-I but also triggered notable suppression of IGF-I receptor (IGF1R) gene expression at pituitary cell level. In our study, IGF1R & insulin receptor (InsR) expressed in carp pituitary cells were both activated by IGF-I treatment, but IGF-I induced PNX and PRL mRNA expression could be blocked only by the inactivators for IGF1R but not InsR. Using a pharmacological approach, the gene expression of PNX and PRL induced by IGF-I was confirmed to be mediated through the PI3K/Akt and MEK1/2/ERK1/2 but not P38MAPK pathways. Our findings, as a whole, suggest that (i) IGF signals can induce PRL gene expression in carp pituitary via IGF1R coupled to PI3K/Akt & MAPK cascades and this stimulatory effect is mediated via local production of PNX, and (ii) LH released in the pituitary can act locally to inhibit both basal & IGF-induced PRL expression and these inhibitory actions are mediated by blocking pituitary expression of PNX & IGF1R. Presentation: Friday, June 16, 2023

Mutant KRAS promotes liver metastasis of colorectal cancer, in part, by upregulating the MEK-Sp1-DNMT1-miR-137-YB-1-IGF-IR signaling pathway

Although the role of insulin-like growth factor-I receptor (IGF-IR) in promoting colorectal liver metastasis is known, the mechanism by which IGF-IR is upregulated in colorectal cancer (CRC) is not defined. In this study, we obtained evidence that mutant KRAS transcriptionally activates IGF-IR gene expression through Y-box-binding protein (YB)-1 upregulation via a novel MEK-Sp1-DNMT1-miR-137 pathway in CRC cells. The mechanistic link between the tumor suppressive miR-137 and the translational regulation of YB-1 is intriguing because epigenetic silencing of miR-137 represents an early event in colorectal carcinogenesis due to promoter hypermethylation. This proposed signaling axis was further verified by the immunohistochemical evaluations of liver metastases from a cohort of 46 KRAS mutant CRC patients, which showed a significant correlation in the expression levels among Sp1, miR-137, YB-1, and IGF-1R. Moreover, suppression of the expression of YB-1 and IGF-IR via genetic knockdown or the pharmacological inhibition of MEK hampers KRAS-driven colorectal liver metastasis in our animal model studies. From a translational perspective, the identification of this KRAS-driven pathway might provide a mechanistic rationale for the use of a MEK inhibitor as an adjuvant, in combination with standard of care, to prevent the recurrence of colorectal liver metastasis in KRAS mutant CRC patients after receiving liver resection, which warrants further investigation.

BRCA1 is Expressed in Uterine Serous Carcinoma (USC) and Controls Insulin-Like Growth Factor I Receptor (IGF-IR) Gene Expression in USC Cell Lines

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. 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. 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. 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.

Insulin-like Growth Factor-I Receptor (IGF-IR) Translocates to Nucleus and Autoregulates IGF-IR Gene Expression in Breast Cancer Cells

The insulin-like growth factor (IGF) system plays an important role in mammary gland biology as well as in the etiology of breast cancer. The IGF-I receptor (IGF-IR), which mediates the biological actions of IGF-I and IGF-II, has emerged in recent years as a promising therapeutic target. The IGF and estrogen signaling pathways act in a synergistic manner in breast epithelial cells. The present study was aimed at investigating 1) the putative translocation of IGF-IR and the related insulin receptor (IR) to the nucleus in breast cancer cells, 2) the impact of IGF-IR and IR levels on IGF-IR biosynthesis in estrogen receptor (ER)-positive and ER-depleted breast cancer cells, and 3) the potential transcription factor role of IGF-IR in the specific context of IGF-IR gene regulation. We describe here a novel mechanism of autoregulation of IGF-IR gene expression by cellular IGF-IR, which is seemingly dependent on ER status. Regulation of the IGF-IR gene by IGF-IR protein is mediated at the level of transcription, as demonstrated by 1) binding assays (DNA affinity chromatography and ChIP) showing specific IGF-IR binding to IGF-IR promoter DNA and 2) transient transfection assays showing transactivation of the IGF-IR promoter by exogenous IGF-IR. The IR is also capable of translocating to the nucleus and binding the IGF-IR promoter in ER-depleted, but not in ER-positive, cells. However, transcription factors IGF-IR and IR display diametrically opposite activities in the context of IGF-IR gene regulation. Thus, whereas IGF-IR stimulated IGF-IR gene expression, IR inhibited IGF-IR promoter activity. In summary, we have identified a novel mechanism of IGF-IR gene autoregulation in breast cancer cells. The clinical implications of these findings and, in particular, the impact of IGF-IR/IR nuclear localization on targeted therapy require further investigation.

P53 Regulates insulin-like growth factor-I receptor gene expression in uterine serous carcinoma and predicts responsiveness to an insulin-like growth factor-I receptor-directed targeted therapy

The role of the insulin-like growth factors (IGF) in endometrial cancer has been well established. The IGF-I receptor (IGF-IR), which mediates the biological actions of IGF-I, is usually overexpressed in endometrial tumours. Uterine serous carcinoma (USC) constitutes a defined histological category among endometrial cancers. Mutation of the p53 gene appears early in the course of the disease and is considered a key event in the initiation of USC. The aim of the present study was to evaluate the potential interactions between p53 and the IGF-IR in USC. In addition, we investigated the role of p53 as a biomarker in IGF-IR targeted therapies. Immunohistochemical analysis in a collection of 35 USC specimens revealed that IGF-IR is highly expressed in primary and metastatic USC. Likewise, p53 was expressed in 85.7% of primary tumours and 100% of metastases. A significant negative correlation between p53 expression and survival was noticed. In addition, using USC-derived cell lines we provide evidence that p53 regulates IGF-IR gene expression via a mechanism that involves repression of the IGF-IR promoter. We show that the mechanism of action of p53 involves interaction with zinc finger protein Sp1, a potent transactivator of the IGF-IR gene. Finally, we demonstrate that USC tumours overexpressing p53 are more likely to benefit from anti-IGF-IR therapies. In summary, we provide evidence that p53 regulates IGF-IR gene expression in USC cells via a mechanism that involves repression of the IGF-IR promoter. The interplay between the p53 and IGF-I signalling pathways is of major basic and translational relevance.

Does metformin influence the insulin-, IGF I- and IGF II-receptor gene expression and Akt phosphorylation in human decidualized endometrial stromal cells?

Objective To assess the effects of metformin on insulin-, IGF I-, and IGF II-receptor gene expression and Akt phosphorylation in decidualized human endometrial stromal cells (ESC) after stimulation with insulin, IGF I and II. Study design ESC were isolated from healthy, regularly cycling women and after two passages decidualized with estrogen/progesterone ± metformin. Cells were incubated with insulin, IGF I or IGF II for 1, 5, and 10 min to assess Akt phosphorylation by Western blot. To investigate the insulin-, IGF I- and IGF II-receptor gene expression ESC were incubated with insulin, IGF I or IGF II for 6 and 24 h. Results Insulin- and IGF I-receptor gene expression in ESC changed significantly after incubation with insulin, IGF I or IGF II. This was further augmented in metformin pretreated cells, while IGF II-receptor gene expression changed particularly after pretreatment with metformin. Akt phosphorylation peaked after 5 min insulin, IGF I and IGF II stimulation in ESC in both control (control 0.08 ± 0.03 vs. insulin 0.74 ± 0.19, IGF I 0.68 ± 0.22, IGF II 0.53 ± 0.13, p < 0.05) and metformin pretreated cells (control 0.03 ± 0.01 vs. insulin 0.75 ± 0.11, IGF I 0.74 ± 0.15, IGF II 0.67 ± 0.09, p < 0.005). However, there was no significant difference between the control and metformin pretreated group. Conclusion Insulin, IGF I and IGF II lead to changes in their receptor gene expression and induced Akt phosphorylation in ESC. These effects were further highlighted in the presence of metformin.

GLUT4 in murine bone growth: from uptake and translocation to proliferation and differentiation

Skeletal growth, taking place in the cartilaginous growth plates of long bones, consumes high levels of glucose for both metabolic and anabolic purposes. We previously showed that Glut4 is present in growing bone and is decreased in diabetes. In the present study, we examined the hypothesis that in bone, GLUT4 gene expression and function are regulated via the IGF-I receptor (IGF-IR) and that Glut4 plays an important role in bone growth. Insulin and IGF-I actions on skeletal growth and glucose uptake were determined using mandibular condyle (MC) organ cultures and MC-derived primary cell cultures (MCDC). Chondrogenesis was determined by following proliferation and differentiation activities using immunohistochemical (IHC) analysis of proliferating cell nuclear antigen and type II collagen expression, respectively. Overall condylar growth was assessed morphometrically. GLUT4 mRNA and protein levels were determined using in situ hybridization and IHC, respectively. Glut4 translocation to the cell membrane was assessed using confocal microscopy analysis of GFP-Glut4 fusion-transfected cells and immunogold and electron microscopy on MC sections; glucose uptake was assayed by 2-deoxyglucose (2-DOG) uptake. Both IGF-I and insulin-stimulated glucose uptake in MCDC, with IGF-I being tenfold more potent than insulin. Blockage of IGF-IR abrogated both IGF-I- and insulin-induced chondrogenesis and glucose metabolism. IGF-I, but not insulin, induced Glut4 translocation to the plasma membrane. Additionally, insulin induced both GLUT4 and IGF-IR gene expression and improved condylar growth in insulin receptor knockout mice-derived MC. Moreover, silencing of GLUT4 gene in MCDC culture abolished both IGF-I-induced glucose uptake and chondrocytic proliferation and differentiation. In growing bone, the IGF-IR pathway stimulates Glut4 translocation and enhances glucose uptake. Moreover, intact Glut4 cellular levels and translocation machinery are essential for early skeletal growth.

Inhibitory Effect of Small Interfering RNA Targeting Insulin-Like Growth Factor-I Receptor in Ovarian Cancer OVCAR3 Cells

Insulin-like growth factor-I receptor (IGF-IR) is widely overexpressed in a variety of human cancers including ovarian cancer. It plays an important role in cancer cell proliferation and tumor growth. In this study, small interfering RNA (siRNA) was used to silence IGF-IR gene expression in the human ovarian cancer cell line OVCAR3 and then its effects on proliferation, apoptosis, angiogenesis, and the growth of tumor cells in vitro and in nude mice were evaluated. Three siRNA sequences for the IGF-IR gene were cloned into expression plasmids and transfected into OVCAR3 cells. The downregulation of IGF-IR expression at both mRNA and protein levels were detected by real-time polymerase chain reaction and western blot analysis. Cell proliferation inhibition rates were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Nude mice (n = 6 per group) were subcutaneously xenografted with 2 × 10(6) OVCAR3 cancer cells. Tumor growth, cellular proliferation (Ki-67 immunohistochemistry), apoptosis, and angiogenesis (CD31 immunohistochemistry) were compared for mice administered either IGF-IR-specific or negative control siRNA over 5 weeks. The mRNA and protein expression of IGF-IR was significantly decreased at 48 hours after transfection, leading to a potent suppression of tumor cell proliferation in vitro. The IGF-IR-specific siRNA dramatically suppressed tumor growth and cellular proliferation, as well as promoted tumor cellular apoptosis and inhibited angiogenesis in an OVCAR3 s.c. xenograft model. The siRNA targeting of IGF-IR can effectively inhibit the growth of ovarian cancer cells and may be used as a potent therapy.

Differential regulation of insulin-like growth factor-I receptor gene expression by wild type and mutant androgen receptor in prostate cancer cells

The progression of prostate cancer from an organ-confined, androgen-sensitive disease to a metastatic one is associated with dysregulation of androgen receptor (AR)-regulated target genes and with a decrease in insulin-like growth factor-I receptor (IGF-IR) expression. To investigate the differential effects of wild type (wt) and mutant AR on IGF-IR levels we employed a series of isogenic prostate-derived cell lines and human xenografts. We show that basal and phosphorylated IGF-IR levels progressively decreased as prostate cancer cells became more tumorigenic and metastatic. In addition, we show that wt, but not mutant, AR along with dihydrotestosterone treatment increased IGF-IR promoter activity and endogenous IGF-IR levels. ChIP analysis show enhanced AR binding to the IGF-IR promoter in AR-overexpressing cells. Finally, wt AR-overexpressing cells display an enhanced proliferation rate. In summary, we provide evidence that activated wt AR enhances IGF-IR transcription in prostate cancer cells via a mechanism that involves AR binding to the IGF-IR promoter. AR mutations alter the ability of the mutated protein to regulate IGF-IR expression. Our results suggest that prostate cancer progression is associated with a decrease in IGF-IR expression that could be the result of impaired ability of AR to stimulate IGF-IR gene expression.

Transcription factor E2F1 is a potent transactivator of the insulin-like growth factor-I receptor (IGF-IR) gene

Objectives The insulin-like growth factor-I receptor (IGF-IR) plays an important role in cancer development. The E2F1 transcription factor activates S-phase promoting genes and mediates apoptosis. Microarray analyses of E2F1-induced genes revealed that genes associated with proliferation as well as apoptosis are upregulated by E2F1. Among other candidate genes, DNA microarrays identified the IGF-IR gene as a putative E2F1 target. The aim of this study was to investigate the involvement of E2F1 in regulation of IGF-IR gene transcription. Methods To examine the potential regulation of IGF-IR gene expression by E2F1, an E2F1 expression vector was transfected into P69 and M12 prostate cancer cell lines, after which IGF-IR levels were measured by Western blots. Transient transfections were used to evaluate IGF-IR promoter activity and chromatin immunoprecipitation (ChIP) assays were employed to assess E2F1-binding to the IGF-IR promoter. Results Results obtained showed that E2F1 expression induced a significant increment in endogenous IGF-IR levels. ChIP assays showed enhanced E2F1-binding to the IGF-IR promoter in E2F1-expressing cells. Transient coexpression of an E2F1 vector along with an IGF-IR promoter-luciferase reporter resulted in a ∼140-fold increase in IGF-IR promoter activity. Furthermore, deletion and bioinformatic analyses indicate that the ability of E2F1 to stimulate IGF-IR promoter activity was correlated with the number of E2F1 sites in the promoter region. Conclusions In summary, we provide evidence that E2F1 regulates IGF-IR gene transcription in prostate cancer cells via a mechanism that involves direct binding to specific elements in the proximal IGF-IR promoter.

P-09 Interactions between androgen receptor and BRCA1 in regulation of IGF-I receptor gene expression in prostate cancer cells

P-09 Interactions between androgen receptor and BRCA1 in regulation of IGF-I receptor gene expression in prostate cancer cells

The effects of resistance exercise on fiber‐type specific GLUT4 and insulin‐like growth factor‐I receptor expression in human skeletal muscle

There has been little research on the effects of resistance exercise on fiber‐type specific gene expression of glucose transporter 4 (GLUT4) and insulin‐like growth factor‐I receptor (IGFIR) expression. Thus, the purpose of this investigation was to measure the effects of an acute bout of resistance exercise (RE) on GLUT4 and IGFIR expression in human skeletal muscle. Six college‐aged males performed a bout of knee‐extensor RE. Individual fibers were isolated from muscle biopsy samples obtained from the vastus lateralis muscle prior to and 4‐hours following RE. Myosin heavy chain analysis was performed on 1/3 of each fiber and 2/3 of the fiber was directly placed in individual tubes containing buffer for the reverse transcription (RT) step of a two‐step RT‐PCR kit (Invitrogen). After RT, the cDNA of all slow‐ (MHC I, N=20 per subject) and fast‐ (MHC IIa and IIa/x, N=30 per subject) twitch fibers were combined for each subject. PCR reactions for GLUT4, IGFIR, and GAPDH (housekeeping gene) were then performed on the samples. ΔΔCT analysis revealed that there were no differences in GLUT4 (slow‐twitch = 0.81, fast‐twitch = 0.72) or IGFIR (slow‐twitch = 0.49, fast‐twitch = −0.11) expression between the pre‐RE and 4‐hour post RE time‐points. These data show that GLUT4 and IGFIR gene expression are not elevated four hours after resistance exercise; however, these genes may be elevated at other times post‐exercise.

Elevated insulin-like growth factor-I receptor (IGF-IR) levels in primary breast tumors associated with BRCA1 mutations

The insulin-like growth factors (IGFs) play a pivotal role in breast cancer. Inherited predisposition to breast and ovarian cancer is associated with germline BRCA1/ BRCA2 mutations. To evaluate the impact of BRCA1 mutations on IGF-IR gene expression, we performed an immunohistochemical analysis of IGF-IR in primary breast tumors from BRCA1 mutation carriers and non-carriers. Results obtained revealed a significant elevation in IGF-IR levels in tumors from BRCA1 mutation carriers compared with non-carriers. To assess the potential inhibitory role of BRCA1 on IGF-IR levels, we infected the BRCA1-deficient HCC1937 cell line with a BRCA1-encoding adenoviral vector. Results of Western blots showed that BRCA1 induced a large reduction in endogenous IGF-IR levels. Furthermore, results of chromatin immunoprecipitation assays indicated that the mechanism of action of BRCA1 involves interaction with Sp1, a potent transactivator of the IGF-IR gene. In conclusion, our data suggests that the IGF-IR gene is a physiologically relevant downstream target for BRCA1 action.

Insulin-like growth factor system gene expression in cervical scrapes from women with squamous intraepithelial lesions and cervical cancer

Background There is ample evidence that the insulin-like growth factors (IGF) system is involved in the development of several types of cancer. The aim of this study was to evaluate the expression levels of IGF-I, IGF-II, IGF binding protein 3 (IGFBP-3) and IGF-I receptor (IGF-IR) in exfoliated cervical cells in cervical carcinogenesis. Methods mRNA levels of IGF-I, IGF-II, IGFBP-3 and IGF-IR were assessed by real-time PCR in 105 cervical scrapes obtained from 16 patients diagnosed with low-grade squamous intraepithelial lesions (LSIL), 24 with high-grade SIL (HSIL), 23 with cervical cancer, and 42 from controls with normal Papanicolau (Pap) test. Results IGF-I mRNA levels were very low and no significant differences were seen between control and other groups. IGF-II mRNA levels were significantly lower in LSIL than in control group (median [arbitrary units]: 0.38 vs. 2.42, P = 0.006) but its expression in HSIL and cervical cancer was similar to the one observed in controls. IGFBP-3 mRNA levels were significantly lower in cancer than in controls (median [arbitrary units]: 0.43 vs. 0.73, P = 0.03). We observed a decrease in IGF-IR gene expression as the SIL degree increased (median for controls, LSIL, HSIL, and cervical carcinoma [arbitrary units]: 31.24, 9.08, 8.95, and 3.56, respectively). IGF-IR mRNA levels were significantly lower in HSIL and cervical cancer in comparison with controls ( P = 0.043 and P < 0.001, respectively). Conclusions The present observations suggest that a reduced expression of IGFBP-3 and IGF-IR can be associated with progression to cervical cancer; the specific role played by the IGF-IR in this process remains unclear.

CLA differently regulates adipogenesis in stromal vascular cells from porcine subcutaneous adipose and skeletal muscle

Conjugated linoleic acid (CLA), a mixture of isomers of linoleic acid, has previously been shown to be able to decrease porcine subcutaneous (SC) adipose tissue levels while increasing the count of intramuscular (IM) adipose tissue in vivo. However, the underlying mechanisms through which it acts are poorly understood. The objective of this study was to investigate the different effects of CLA on adipogenesis in cultured SC adipose tissue and IM stromal vascular cells obtained from neonatal pigs. As shown here, trans-10, cis-12 CLA decreased the expression of adipocyte-specific genes as well as adipose precursor cell numbers and the accumulation of lipid in cultured SC adipose tissue stromal vascular cells. However, the cis-9, trans-11 CLA did not alter adipogenesis in SC cultures. On the other hand, both CLA isomers increased the expression of adipocyte-specific genes in IM cultures, together with the increasing accumulation of lipid and Oil Red O-stained cells. Collectively, these data show that CLA decreases SC adipose tissue but increases IM adipose tissue by different regulation of adipocyte-specific gene expression. These results suggest that adipogenesis in IM adipocytes differs from that in SC adipocytes.

Identification of two isoforms of Atlantic halibut insulin-like growth factor-I receptor genes and quantitative gene expression during metamorphosis

Insulin-like growth factor-I (IGF-I) is an important regulator of growth and development in vertebrates. Both the endocrine and paracrine actions of IGF-I are mediated through ligand-binding to a membrane-bound IGF-I receptor (IGF-IR). The characterization of this receptor and subsequent expression studies thus help elucidate the endocrine regulation of developmental processes. As other flatfish species, the Atlantic halibut ( Hippoglossus hippoglossus) undergoes a dramatic larval metamorphosis. This process is largely under endocrine control, and data indicate that IGF-I could be a key regulator. IGF-I content increases up to late pre-metamorphosis and decreases during metamorphosis. The IGF-IR has, however, not been studied during flatfish metamorphosis. To examine IGF-IR gene expression, two IGF-IR mRNA were cloned and sequenced. These partial sequences share high identity (≥ 95%) and similarity (≥ 97%) with other fish IGF-IR and lower identity (≥ 77%) and similarity (≥ 83.5%) with Japanese flounder insulin receptors. The expression of mRNA for both IGF-IR was analyzed by quantitative real-time RT-PCR during six larval developmental stages from pre- to post-metamorphosis. IGF-IR1 and IGF-IR2 mRNA are differentially expressed during metamorphosis, but if this indicates an isoform-specific regulation of developmental processes by circulating and/or locally-secreted IGF-I is unclear. Both IGF-IR genes are down-regulated in halibut larvae experiencing arrested metamorphosis, suggesting the IGF-I system is critical for metamorphic success in halibut.

Down regulation of IGF-I and IGF-IR gene expression in right atria tissue of ventricular septal defect infants with right atria hypoxemia

Background Our previous studies showed serum insulin-like growth factor-I (IGF-I) concentrations significantly decreased in infants with congenital ventricular septal defect (VSD) and that they were associated with increased concentrations of growth hormone. In order to confirm the relationship between IGF-I axis and VSD, we further compared the IGF-I and insulin-like growth factor-I receptor(IGF-IR) gene expressions in the cardiac tissue of VSD infants. Methods Right atrium biopsies of 27 infants were studied. Five infants not having VSD were classified as controls (Group I). Twenty VSD patients were then divided into 2 groups according to their shunting magnitude index (level of pulmonary vascular resistance compared with systemic vascular resistance, Qp/Qs). VSD patients with minor shunts (Qp/Qs < 1.7) were classified as Group II; VSD patients with larger shunts (Qp/Qs ≥ 2) as Group III. Besides, seven tetralogy of fallot (TOF) with shunt (Qp/Qs > 4) infants were classified as the Group IV. A non-radioactive DIG-RNA probe detection system, western blotting and immunohistochemistry were used to detect the gene expression levels and protein products of IGF-I and IGF-IR in the right atrium samples of VSD infants. Results The relative protein levels of IGF-I were 0.96 ± 0.05, 0.43 ± 0.03, 0.15 ± 0.04, 0.12 ± 0.03 and IGF-IR were 0.80 ± 0.08, 0.57 ± 0.03, 0.38 ± 0.02, 0.24 ± 0.04 in the right atrium of 4 group patients. The relative mRNA levels of IGF-I were 0.95 ± 0.01, 0.41 ± 0.03, 0.29 ± 0.05, 0.15 ± 0.01 and IGF-IR were 0.85 ± 0.05, 0.56 ± 0.03, 0.17 ± 0.01, 0.18 ± 0.01, respectively. There was a significantly greater but more gradual decrease in protein levels and in mRNA levels of IGF-I and IGF-IR in Group II ( p < 0.05), Group III and IV ( p < 0.01) than in Group I. The results of immunohistochemistry also demonstrated a similar decrease in VSD patients. In addition, the decrease of mRNA and protein levels in IGF-I/ IGF-IR of VSD patients show related to the saturation of oxygen in the right atrium and the ratio of systolic right ventricular pressure to left ventricular pressure. Conclusion We further confirmed the down regulation of IGF-I/IGF-IR in cardiac tissue of VSD infants and the decrease to be associated with shunt magnitude and the severity of hypoxemia in the cardiac chamber of VSD.

Estrogen receptor regulates insulin-like growth factor-I receptor gene expression in breast tumor cells: involvement of transcription factor Sp1

The insulin-like growth factors, IGF-I and IGF-II are a family of mitogenic polypeptides with important roles in growth and differentiation. The biological actions of the IGFs are mediated by the IGF-I receptor (IGF-IR), a cell-surface tyrosine kinase, whose activation by serum IGF-I seems to be a key step in breast cancer initiation. Evidence accumulated indicates that estrogens stimulate the expression and activity of IGF axis components. The aim of our study was to examine the transcriptional mechanisms involved in regulation of IGF-IR gene expression by the estrogen receptor (ER). For this purpose, transient transfections using an IGF-IR promoter-luciferase reporter plasmid were performed in breast cancer-c derived ER-positive MCF-7 cells and isogenic ER-negative C4 cells. To examine the potential involvement of zinc-finger nuclear proteins in the transactivating effect of estrogens, chromatin immunoprecipitation (ChIP) experiments were performed using an Sp1 antibody, along with the Sp1-family-binding inhibitor Mithramycin A. The results obtained indicate that basal IGF-IR promoter activity was 5.8-fold higher in MCF-7 than in C4 cells. Estradiol treatment significantly activated the IGF-IR promoter in MCF-7, but not in C4 cells. Furthermore, the estrogen responsive region in the IGF-IR promoter was mapped to a GC-rich sequence located between nucleotides -40 and -188 in the 5' flanking region. ChIP experiments revealed that at least part of the estrogen effect on IGF-IR expression was mediated through activation of the Sp1 transcription factor. In summary, our studies demonstrate that IGF-IR gene transcription in breast cancer cells is controlled by interactions between ERalpha and Sp1. Dysregulated expression of the IGF-IR gene may have pathologic consequences with relevance in breast cancer etiology.

Caveolin-1 up-regulates IGF-I receptor gene transcription in breast cancer cells via Sp1- and p53-dependent pathways

The insulin-like growth factor (IGF) system plays an important role in the biology of breast cancer. Most of the biological actions of IGF-I and IGF-II are mediated by the IGF-I receptor (IGF-IR), a membrane-bound heterotetramer with potent antiapoptotic and cell survival activities. Caveolin-1 (Cav-1) is one of the main components of caveolae, and it has been shown to interact with multiple signaling molecules. In view of the important roles of IGF-IR and Cav-1 in oncogenically transformed mammary gland cells, in the present study we addressed the potential regulation of IGF-IR gene expression by Cav-1. The results obtained showed that MCF7/Cav-1 cells, expressing the Cav-1 gene in a stable manner, contain significantly higher levels of IGF-IR protein and mRNA than native MCF7 cells. These elevated levels of expression are mediated at the level of transcription, as shown by the results of experiments showing that the activity of the proximal IGF-IR promoter was higher in Cav-1-expressing MCF7 cells than in untransfected MCF7 cells. Furthermore, in subcellular localization studies, intensive IGF-IR staining in membrane ruffles and projections in MCF7/Cav-1 cells were noted, in contrast to typical membrane staining in MCF7 cells. In addition, we demonstrated that transcriptional activation of the IGF-IR gene by Cav-1 requires an intact p53 signaling pathway, since Cav-1 was unable to elevate IGF-IR levels in p53-null cells. Finally, the effect of Cav-1 was associated with an elevation in the levels of Sp1, a zinc-finger protein with important roles in IGF-IR gene transactivation. In summary, we identified the IGF-IR gene as a downstream target for Cav-1 action in breast cancer cells.

Dietary Supplementation with Zinc Oxide Increases IGF-I and IGF-I Receptor Gene Expression in the Small Intestine of Weanling Piglets

This study was conducted to investigate the mechanism for the effect of elevated levels of dietary zinc oxide (ZnO) in enhancing the intestinal growth of weanling piglets. In Experiment 1, 4-wk-old (8.1 +/- 0.6 kg) crossbred barrows (n = 36) were assigned randomly to 1 of the 2 dietary groups, with 6 pens/group (3 pigs/pen). One group was fed the basal diet containing 100 mg Zn/kg diet. The other group was fed the basal diet supplemented with ZnO to provide 3000 mg Zn/kg diet. Pigs consumed their feed ad libitum for 14 d. In Experiment 2, 4-wk-old (7.6 +/- 0.16 kg) crossbred barrows (n = 16) were housed individually and assigned to 1 of the 2 dietary groups (8 pigs/group) as in Experiment 1, except that the 2 groups were pair-fed the same amount of feed. At the end of a 14-d treatment period, all of the pigs in both Experiments 1 and 2 were weighed, feed consumption was measured, and blood samples were collected for assays of insulin-like growth factor-I (IGF-I). In addition, 1 pig from each pen in Experiments 1 and 2 was selected randomly to obtain the small-intestinal mucosa for analyzing IGF-I and IGF-I receptor (IGF-IR) gene expression and to determine the small-intestinal morphology. In Experiment 1, dietary supplementation of ZnO increased (P < 0.05) the daily body weight gain and daily feed intake. In Experiment 2, dietary supplementation of ZnO increased (P < 0.05) the daily body weight gain and feed conversion efficiency. In both experiments, the villous height of the small-intestinal mucosa and both the mRNA and protein levels for IGF-I and IGF-IR in the small intestine were markedly enhanced (P < 0.05) by feeding elevated levels of Zn. Serum IGF-I levels did not differ between the control and Zn-supplemental groups in either experiment. Collectively, these results suggest that dietary Zn supplementation exerts its beneficial effects on the intestinal growth of weanling piglets through increasing IGF-I and IGF-IR expression in the small-intestinal mucosa.