O-244 Androgen levels and their predictive value in women with different ovarian responses

Study question

Do androgen levels impact oocyte yield during ovarian stimulation and how predictive are they for distinct ovarian response?

Summary answer

Testosterone positively correlates with the number of oocytes retrieved in all patients. DHEA-S appears more specific by only correlating significantly in poor responding women.

What is known already

Androgens are involved in the initiation of primordial follicle recruitment and early development. Testosterone and DHEA-S increase the number of growing follicles by reducing follicular atresia. A reduction in androgen levels can be observed with diminished ovarian reserve and advanced age. To standardize the definition of POR Bologna criteria have been elaborated including age, laboratory or sonographic ovarian reserve and low ovarian response in previous stimulations. The mentioned markers have been reviewed concerning its predictive power for POR by the POSEIDON analysis and divided into four subgroups. To date androgen levels are not raised to stratify POR in these classifications.

Study design, size, duration

All women were recruited in the division for reproductive medicine at the University Hospital Heidelberg. The patients’ files were retrospectively analyzed for androgen levels before ovarian stimulation and outcome. A classification between poor and normal response was performed according to Bologna criteria.

Participants/materials, setting, methods

All patients provided written informed consent. Blood samples were analyzed from serum drawn on day 2 to 5 of the menstrual cycle before ovarian stimulation. Statistical analysis was performed with SPSS; statistical significance was set to p < = 0.05.

Main results and the role of chance

Valid data for analysis was available in 335 cycles, 238 were scaled in normal (NOR), 97 in poor ovarian response (POR). Statistics in both subgroups were performed concerning age, AMH, count of retrieved oocytes, DHEA-S and testosterone with significant lower AMH as well as androgen levels, oocyte yields and a higher median age in the POR group. An expected significant positive correlation between AMH and retrieved oocytes was confirmed in both subgroups (p=.000 and .004). Increasing age negatively correlates with the number of retrieved oocytes after ovarian stimulation in NOR (p=.003), but not in POR (p=.441) patients suggesting age as less powerful predictive marker for oocyte yield in those patients.

In addition, a positive correlation for testosterone and retrieved oocytes merely reached significance in all analyzed cycles independently of different ovarian responses. On the contrary DHEA-S levels and oocyte counts cohered with a marginal significance (p=.05) only in POR patient cycles. Serum levels for DHEA-S positively correlated with the variable “oocyte count ≥ 3” in the POR group (OR 1.006, 95% CI, 0.999- 1.014

Limitations, reasons for caution

The results are based on a limited sample size. Therefore, results need to be proven in further studies including further aspects affecting ovarian response.

Wider implications of the findings

The significant correlation between pre-stimulatory DHEA-S levels in POR for oocyte yield on the contrary to NOR, supports the experimental supplementation with DHEA in this subgroup, aiming to improve outcomes during ovarian stimulation. Testosterone is less specific for estimating ovarian response in both subgroups.

Trial registration number

n.A.

O-080 Activated AKT/mTOR signalling in peripheral blood of women with premature ovarian insufficiency and its correlation with variable FMR1 expression profiles

Study question

How predictive are gene expression levels of AKT/mTOR-signalling-pathway genes in peripheral blood of patients with premature ovary insufficiency (POI) and is there a link to FMR1-expression?

Summary answer

AKT1, TSC2, mTOR, S6K and FOXO3-expression-levels are significantly upregulated in POI-patients and demonstrate a positive correlation with FMR1-expression-level in case of mTOR-, S6K and FOXO3.

What is known already

The AKT/mTOR-signalling-pathway is involved in a range of cellular functions. In female germline it regulates early follicular-activation and follicular-pool-maintenance. Over the past few years AKT-activation has been experimentally applied to induce follicular maturation in POI-patients. Additionally, first evidence of a linked FMR1 – AKT/mTOR signaling in female germline have been reported.

FMR1 is a major control gene in folliculogenesis. Due to increased (CGG)-triplet-numbers (54 < n < 200) in its 5′-untranslated-region, named premutation, increased FMR1-expression-levels and reduced FMRP-production have been described, associated with POI in 20% of cases. A former study found premutation independent, large transcript-level-variances of FMR1 in leukocyte RNA-samples of POI-patients.

Study design, size, duration

74 POI patients and 56 fertile controls were prospectively enrolled in this study. Accordingly, expression levels of genes associated with the AKT/mTOR-signaling pathway and FMR1 were analyzed and correlated on the mRNA level of their leukocytes.

Participants/materials, setting, methods

All patients provided written informed consent. mRNA was extracted from EDTA blood after lysis; quantitative expression analyses of FMR1, AKT, mTOR, S6K, FOXO3, FOXO1 genes were performed with specific TaqMan-Assays. Statistical analyses was performed with SPSS; statistical significance was set to P < 0.05.

Main results and the role of chance

Gene expression levels of AKT1, TSC2, mTOR, S6K, FOXO3 are significant higher in POI patients compared to controls (P < 0.009 or less).

The rate of FMR1-expression is highly correlated with mTOR-, S6K and FOXO3-expression levels (P < 0.001) in all patients, in addition. When grouped according to ovarian reserve this effect is more pronounced in POI than in control patients. Additionally, the correlation of FMR1 with FOXO3 remained significant only in the POI subgroup.

The upregulation of AKT/mTOR-signaling in POI may reflect a compensative mechanism in POI aiming the activation of the last remaining follicles.

The linkage of FMR1 with AKT/mTOR-signalling in peripheral blood comparable to prior results from germline, support its putative impact on the pathogenesis of POI and other folliculogenesis related disorders, such as poor ovarian response.

Limitations, reasons for caution

Results are based on limited patient numbers. More patients, stratified for age and other risks factors, are needed to further elucidate this mechanism.

Wider implications of the findings

This is the first evidence that FMR1 is linked to an AKT/mTOR activation in POI potentially involved in its pathogenesis. Such a marker in peripheral blood offers a perspective towards its usability as a predictive tool in the diagnostics and prognosis of POI, if results are consistent in further studies.

Trial registration number

not applicable

Influence of leptin, androgens and insulin sensitivity on increased GH response to clonidine in lean patients with polycystic ovary syndrome

Our aim was to investigate whether insulin sensitivity, leptin, androgen or estradiol levels are associated with disturbed GH response to clonidine in lean patients with polycystic ovary syndrome. Fourteen lean polycystic ovary syndrome patients, 11 ovulatory patients presenting idiopathic hirsutism and 10 non-hirsute, normal women with regular cycles paired for age and BMI were included in a cross-sectional study. Baseline hormonal and metabolic variables were assessed and analyzed in association with GH response to oral administration of 0.3 mg of clonidine. Delta GH was significantly higher in the PCOS group than in the IH and control groups (p = 0.014). The groups were similar in terms of body mass index, insulin, glucose, total and HDL cholesterol, triglycerides and estradiol levels. Free androgen index (r = 0. 454, p = 0.015) and leptin (r = 0.419, p = 0.023) were positively correlated with the homeostasis model assessment. The homeostasis model assessment was the only variable that significantly correlated with GH response to clonidine (r = 0.375, p = 0.029) (vs. estradiol, free androgen index, leptin and LH). Nonetheless, when the analysis was adjusted for leptin levels and free androgen index, the statistical significance of this correlation was lost. The increased GH secretion observed in our lean PCOS patients may be associated with slight changes in insulin sensitivity, even in the absence of clinical evidence of insulin resistance. This association seems to be modulated by leptin and androgen levels.

Insulin-Like Growth Factor 1 Receptor mRNA Expression and Autophosphorylation in Human Myometrium and Leiomyoma

Uterine leiomyomas are the most common tumors of the genital tract. Growth factors seem to be implicated in the development of leiomyoma. The aim of this study was to determine insulin-like growth factor 1 receptor (IGF-1-R) mRNA levels and IGF-1-R tyrosine kinase activity in normal myometrium and leiomyoma. Plasma membranes of myometrium and leiomyoma of 14 women subjected to hysterectomy were prepared, and samples were incubated in the absence or presence of recombinant human IGF-1 to assess the tyrosine kinase activity (Western blot). Reverse-transcriptase polymerase chain reaction with specific primers for IGF-1-R was used to determine IGF-1-R mRNA levels. IGF-1-R mRNA levels in myometrium (0.8216 +/- 0.096) and in leiomyoma (0.7905 +/- 0.136) were not statistically significantly different (p = 0.648). The degree of IGF-1-R autophosphorylation stimulated by recombinant IGF-1 was not different in myometrium (1.020 +/- 0.120) and leiomyoma (1.620 +/- 0.656) either (p = 0.075). There was no difference in IGF-1-R expression and IGF-1-R autophosphorylation between normal myometrium and leiomyoma.

Clinical, metabolic and endocrine parameters in response to metformin in obese women with polycystic ovary syndrome: a randomized, double-blind and placebo-controlled trial

There is still some controversy concerning the effects of metformin in the treatment of Polycystic Ovary Syndrome (PCOS). The aim of this study was to asses the effect of metformin on clinical, metabolic and hormone parameters in obese women with PCOS. Thirty obese, non-diabetic women with PCOS received 500 mg of metformin or placebo, TID, over 90 days. Assessed parameters included body mass index, waist-to-hip ratio, blood pressure, FSH, LH, total testosterone, SHBG, fasting insulinemia, insulin-to-glucose ratio, total, HDL and LDL cholesterol, triglycerides, and menstrual cycles before and after the use of the drugs. Before treatment, patients did not differ in the two groups. After 90 days of metformin use, PCOS women presented significantly lower levels of total testosterone (p = 0.030) and total cholesterol (p = 0.023) compared to the women that used placebo. The other parameters did not differ between the groups. In conclusion, obese women with PCOS may benefit from the use of metformin through the reduction of hyperandrogenemia, total cholesterol, and possibly by restoration of regular menstrual cycles. Further studies with longer follow-ups are necessary to determine cardiovascular and endometrial metformin benefits and insulin-resistance decrease in women with polycystic ovary syndrome.

Vaginal adenosis in a non-diethylstilbestrol-exposed 6-year-old patient

Vaginal adenosis is rare, and it is defined as the presence of metaplastic cervical or endometrial epithelium within the vaginal wall. It is associated with in utero exposition to diethylstilbestrol and a high risk of vaginal carcinomas. A case of vaginal adenosis arising in a non-diethylstilbestrol-exposed 6-year-old patient is presented. Few cases have been described in children and adolescents, and since the withdrawal of diethylstilbestrol from the market, this condition is rarely described in the medical literature. However, it should be considered as a possible diagnosis in girls with persistent vaginal discharge.

Leptin concentrations in hirsute women with polycystic ovary syndrome or idiopathic hirsutism: influence on LH and relationship with hormonal, metabolic, and anthropometric measurements

BACKGROUND

The known association between leptin, obesity and insulin action suggests that leptin may have a role in polycystic ovarian syndrome (PCOS) but this has only been addressed peripherally.

METHODS

We assessed the influence of leptin on LH and investigated the relationship between leptin and body mass index (BMI), waist:hip ratio (WHR), androgen concentrations, fasting insulin and insulin:glucose ratio (IGR) in 27 women with PCOS and in 20 age- and weight-matched women with regular, ovulatory menstrual cycles and idiopathic hirsutism (IH).

RESULTS

Leptin concentrations were significantly higher in obese PCOS women than in normal weight women with either PCOS or IH (P = 0.0028), but did not differ between obese women with PCOS and IH. WHR, insulin concentrations and IGR were significantly higher in obese PCOS patients in comparison with the three other groups. In IH patients, the association between leptin concentrations and WHR was lost after adjustment for BMI. In PCOS patients, a significant correlation was observed between leptin and fasting insulin concentrations, IGR, WHR and LH. After adjustment for BMI, only the correlation with LH remained significant. A stepwise regression model was set up with LH as the dependent variable to test the hypothesis that the concentrations of leptin might be modulating the concentrations of LH in PCOS patients. The relationship of LH concentrations with IGR was found to be BMI dependent. In contrast, leptin concentrations contributed negatively and significantly to LH concentrations, independently of either BMI or IGR.

CONCLUSIONS

We speculate that the known attenuation in basal or stimulated response of LH in obese PCOS patients might be related to leptin resistance, which could influence LH hypersecretion. In IH ovulatory patients, normal LH concentrations suggest the presence of preserved regulatory mechanisms of GnRH pulsatility. Further studies are needed to specifically investigate the proposed correlation between leptin and GnRH modulation in PCOS.

Expression of glucose transporter 1 in human endometrial and decidual tissue

Regulation of endometrial glucose transport is important for the decidualization process. Therefore, we have examined the expression of the glucose transporter protein isoform 1 (GLUT1) in endometrial samples during the menstrual cycle and in decidual tissue by immunohistochemistry, and GLUT1 mRNA by RNase protection assays. GLUT1 protein was not detected in proliferative endometrial samples, but was highly expressed in decidual tissue. Placental tissue was highly positive. GLUT1 mRNA could be detected in endometrial samples with an increase in endometria of the late secretory phase (day 25-28) and maximum concentration in the decidua of the 9th-10th week of gestation. Our results show that GLUT1 is differentially expressed in the different phases of the human endometrium with a maximum in the human decidua. Therefore, GLUT1 may be an important marker for endometrial differentiation.

Cycle modulation of insulin-like growth factor-binding protein 1 in human endometrium

Endometrium is one of the fastest growing human tissues. Sex hormones, estrogen and progesterone, in interaction with several growth factors, control its growth and differentiation. Insulin-like growth factor 1 (IGF-1) interacts with cell surface receptors and also with specific soluble binding proteins. IGF-binding proteins (IGF-BP) have been shown to modulate IGF-1 action. Of six known isoforms, IGF-BP-1 has been characterized as a marker produced by endometrial stromal cells in the late secretory phase and in the decidua. In the current study, IGF-1-BP concentration and affinity in the proliferative and secretory phase of the menstrual cycle were measured. Endometrial samples were from patients of reproductive age with regular menstrual cycles and taking no steroid hormones. Cytosolic fractions were prepared and binding of (125)I-labeled IGF-1 performed. Cross-linking reaction products were analyzed by SDS-polyacrylamide gel electrophoresis (7.5%) followed by autoradiography. (125)I-IGF-1 affinity to cytosolic proteins was not statistically different between the proliferative and secretory endometrium. An approximately 35-kDa binding protein was identified when (125)I-IGF-1 was cross-linked to cytosol proteins. Secretory endometrium had significantly more IGF-1-BP when compared to proliferative endometrium. The specificity of the cross-linking process was evaluated by the addition of 100 nM unlabeled IGF-1 or insulin. Unlabeled IGF-1 totally abolished the radioactivity from the band, indicating specific binding. Insulin had no apparent effect on the intensity of the labeled band. These results suggest that IGF-BP could modulate the action of IGF-1 throughout the menstrual cycle. It would be interesting to study this binding protein in other pathologic conditions of the endometrium such as adenocarcinomas and hyperplasia.

Increase in serum leptin concentrations in women undergoing controlled ovarian hyperstimulation for assisted reproduction

The ob gene product might influence the hypothalamo-pituitary axis and ovarian function directly via specific ovarian receptors. Premenopausal women have higher leptin concentrations compared to postmenopausal controls. In this study, we determined changes in leptin serum concentrations under the influence of supraphysiological estradiol levels during controlled ovarian hyperstimulation. In a prospective study of 20 patients undergoing in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI), morning blood samples were collected to determine leptin and estradiol concentrations on day 3 and day 9 of the stimulation cycle and on alternate days until ovulation induction. There was a significant increase in serum leptin concentrations from day 3 to day 9 (9.87 +/- 1.5 ng/ml on day 3 and 13.8 +/- 2.1 ng/ml on day 9 respectively). No further increase in leptin was observed until the day of ovulation induction. These data further underline the role of leptin as a hormone of reproduction.

Leptin activates PI-3 kinase in C2C12 myotubes via janus kinase-2 (JAK-2) and insulin receptor substrate-2 (IRS-2) dependent pathways

We have recently shown that leptin mimicks insulin effects on glucose transport and glycogen synthesis through a phosphatidylinositol-3 (PI) kinase dependent pathway in C2C12 myotubes. The aim of the present study was to identify the signalling path from the leptin receptor to the PI-3 kinase. We stimulated C2C12 myotubes with insulin (100 nmol/l, 5 min) or leptin (0.62 nmol/l, 10 min) and determined PI-3 kinase activity in immunoprecipitates with specific non-crossreacting antibodies against insulin-receptor substrate (IRS 1/IRS 2) and against janus kinase (JAK 1 and JAK 2). While insulin-stimulated PI-3 kinase activity is detected in IRS-1 and IRS-2 immunoprecipitates, leptin-stimulated PI-3 kinase activity is found only in IRS-2 immunoprecipitates, suggesting that the leptin signal to PI-3 kinase occurs via IRS-2 and not IRS-1. Leptin-, but not insulin-stimulated PI-3 kinase activity is also detected in immunoprecipitates with antibodies against JAK-2, but not JAK-1. The data suggest that JAK-2 and IRS-2 couple the leptin signalling pathway to the insulin signalling chain. Since we have also detected leptin-stimulated tyrosine phosphorylation of JAK-2 and IRS-2 in C2C12 myotubes it can be assumed that leptin activates JAK-2 which induces tyrosine phosphorylation of IRS-2 leading to activation of PI-3 kinase. As we could not detect the long leptin receptor isoform in C2C12 myotubes we conclude that this signalling pathway is activated by a short leptin receptor isoform.

Leptin stimulates glucose transport and glycogen synthesis in C2C12 myotubes: evidence for a P13-kinase mediated effect

It was recently shown that leptin impairs insulin signalling, i.e. insulin receptor autophosphorylation and insulin-receptor substrate (IRS)-1 phosphorylation in rat-1 fibroblasts, NIH3T3 cells and HepG2 cells. To evaluate whether leptin might impair the effects of insulin in muscle tissue we studied the interaction of insulin and leptin in a muscle cell system, i.e. C2C12 myotubes. Preincubation of C2C12 cells with leptin (1-500 ng/ml) did not significantly affect insulin stimulated glucose transport and glycogen synthesis (1.8 to 2 fold stimulation); however, leptin by itself (1 ng/ml) was able to mimic approximately 80-90% of the insulin effect on glucose transport and glycogen synthesis. Both glucose transport as well as glycogen synthesis were inhibited by the phosphatidylinositol-3 (PI3)-kinase inhibitor wortmannin and the protein kinase C inhibitor H7 while no effect was observed with the S6-kinase inhibitor rapamycin. We determined whether the effect of leptin occurs through activation of IRS-1 and PI3-kinase. Leptin did not stimulate PI3-kinase activity in IRS-1 immunoprecipitates; however, PI3-kinase activation could be demonstrated in p85 alpha immunoprecipitates (3.04 +/- 1.5 fold of basal). In summary the data provide the first evidence for a positive crosstalk between the signalling chain of the insulin receptor and the leptin receptor. Leptin mimics in C2C12 myotubes insulin effects on glucose transport and glycogen synthesis most likely through activation of PI3-kinase. This effect of leptin occurs independently of IRS-1 activation in C2C12 cells.

Insulin receptor tyrosine kinase activity in colon carcinoma

Colon carcinoma is the most common tumor of the gastrointestinal tract. According to some investigators, insulin, epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) man be involved in the neoplastic proliferation. Insulin-binding and receptor tyrosine kinase activity were investigated in colon carcinomas and in normal colons. The insulin receptor concentration, as shown by binding assays, was 17.4 +/- 4.3 fmol/micrograms in normal colon and 29.69 +/- 9.4 fmol/micrograms in colon carcinoma. Nevertheless, the insulin affinity of the receptor was similar in both groups (Kd identical to 1 nM). Both normal and neoplastic colon showed phosphorylation of the insulin receptor. The electrophoretic migration of the beta-subunit of the insulin receptors purified from colon carcinomas was similar to that of normal colon and both tissues demonstrated an insulin-dependent autophosphorylation. The receptor tyrosine kinase activity was measured by the incorporation of [gamma 32P]ATP into the beta-subunit. The basal and the insulin-stimulated tyrosine kinase activities were significantly higher in colon carcinomas compared to normal colon tissues (2.2 and 1.6 times, respectively). Understanding the metabolism of neoplastic cells may contribute to the development of prevention strategies as well as new therapies. It is now necessary to study other steps of the insulin signal transduction pathway, such as insulin receptor substrate 1 phosphorylation.

Characterization of receptors for insulin-like growth factor type I on cultured human endometrial stromal cells: downregulation by progesterone

Because insulin-like growth factor type I (IGF-I) is reputed to be involved in the endometrial decidualization, we analyzed the expression of IGF-I receptors in an in vitro system of human endometrial stromal cells. Competitive binding studies of both intact stromal cells and membrane preparation indicated the presence of specific components with high affinity for binding IGF-I. Half-maximum displacement was obtained with 2.3 nmol/l native IGF-I, whereas insulin was unable to achieve half-maximum displacement even at higher concentrations. This IGF-I binding component was found to be a saturable protein in respect of the radioligand [125I]IGF-I, with a dissociation constant of 0.16 nmol/l. Affinity cross-linking studies revealed a labelled band of approximate relative molecular mass 135000, corresponding to the known alpha-subunit of IGF-I receptor. This band was significantly inhibited dose-dependently by the IGF-I receptor monoclonal antibody alpha-IR3 or native IGF-I, suggesting that the IGF-I binding component in the membrane of stromal cells has the identity of the alpha-subunit of IGF-I receptor. Cell proliferation in vitro was stimulated by progesterone. Furthermore, progesterone downregulated the [125I]IGF-I binding activity by downregulation of the IGF-I membrane receptor of human endometrial stromal cells. These data show that the IGF-I receptor is a functionally integral component of the stromal cell membrane structure, and its expression might be directly modulated by progesterone and, therefore, might play an important role in the preparation of the stroma for successful embryo implantation.

Tumor necrosis factor-alpha- and hyperglycemia-induced insulin resistance. Evidence for different mechanisms and different effects on insulin signaling

Inhibition of insulin receptor signaling by high glucose levels and by TNF-alpha was recently observed in different cell systems. The aim of the present study was to characterize the mechanism of TNF-alpha-induced insulin receptor inhibition and to compare the consequences of TNF-alpha- and hyperglycemia-induced insulin receptor inhibition for signal transduction downstream from the IR. TNF-alpha (0.5-10 nM) and high glucose (25 mM) showed similar rapid kinetics of inhibition (5-10 min, > 50%) of insulin receptor autophosphorylation in NIH3T3 cells overexpressing the human insulin receptor. TNF-alpha effects were completely prevented by the phosphotyrosine phosphatase (PTPase) inhibitors orthovanadate (40 microM) and phenylarsenoxide (35 microM), but they were unaffected by the protein kinase C (PKC) inhibitor H7 (0.1 mM), the phosphatidylinositol-3 kinase inhibitor wortmannin (5 microM), and the thiazolidindione troglitazone (CS045) (2 microgram/ml). In contrast, glucose effects were prevented by PKC inhibitors and CS045 but unaffected by PTPase inhibitors and wortmannin. To assess effects on downstream signaling, tyrosine phosphorylation of the following substrate proteins of the insulin receptor was determined: insulin receptor substrate-1, the coupling protein Shc, focal adhesion kinase (FAK125), and unidentified proteins of 130 kD, 60 kD. Hyperglycemia (25 mM glucose) and TNF-alpha showed analogous (> 50% inhibition) effects on tyrosine phosphorylation of insulin receptor substrate-1, Shc, p60, and p44, whereas opposite effects were observed for tyrosine phosphorylation of FAK125, which is dephosphorylated after insulin stimulation. Whereas TNF-alpha did not prevent insulin-induced dephosphorylation of FAK125, 25 mM glucose blocked this insulin effect completely. In summary, the data suggest that TNF-alpha and high glucose modulate insulin receptor-signaling through different mechanisms: (a) TNF-alpha modulates insulin receptor signals by PTPase activation, whereas glucose acts through activation of PKC. (b) Differences in modulation of the insulin receptor signaling cascade are found with TNF-alpha and high glucose: Hyperglycemia-induced insulin receptor inhibition blocks both insulin receptor-dependent tyrosine phosphorylation and dephosphorylation of insulin receptor substrate proteins. In contrast, TNF-alpha blocks only substrate phosphorylation, and it does not block insulin-induced substrate dephosphorylation. The different effects on FAK125 regulation allow the speculation that long-term cell effects related to FAK125 activity might develop in a different way in hyperglycemia- and TNF-alpha-dependent insulin resistance.

Insulin- and insulin-like growth-factor-I receptor tyrosine-kinase activities in human renal carcinoma

We studied expression and functional characteristics of the insulin- and insulin-like-growth-factor-I (IGF-I) receptors in human renal carcinoma. Ligand-binding properties and tyrosine-kinase activity of both receptors, as well as the expression of the 2 isoforms of the human insulin receptor (HIR-A and -B) were analyzed in renal carcinoma and normal adjacent kidney tissue of 8 adult patients. Partially purified insulin- and IGF-I receptors from normal and renal cell carcinoma tissue possessed identical affinities for their ligands. Renal cell carcinoma, however, contained 3- to 4-fold more specific insulin-binding sites and 2-fold more IGF-I binding sites than adjacent normal kidney tissue. In addition, we determined the relative content of insulin/IGF-I receptor hybrids in both tissues. Renal cell carcinoma and adjacent normal tissue revealed similar amounts of insulin/IGF-I receptor hybrids, i.e., 44 +/- 8.2% of tracer IGF-I binding in normal tissue and 46 +/- 12.0% in renal cell carcinoma. When equal amounts of insulin- and IGF-I receptor protein were studied, we found significantly increased receptor autophosphorylation and elevated substrate phosphorylation in carcinoma tissue. To assess whether the differences in insulin-receptor tyrosine-kinase activity were caused by an altered pattern of insulin receptor isoform expression, we determined mRNA levels for HIR-A and -B. The 2 insulin receptor isoforms were, however, expressed in highly variable ratios in both normal and tumor tissue. Our experiments show that renal carcinoma expresses an elevated amount of insulin- and IGF-I receptor protein with increased specific autophosphorylation and tyrosine-kinase activity each. The increase of insulin-receptor tyrosine-kinase activity in renal carcinoma cannot be explained by an altered expression pattern of insulin receptor isoforms.

Mechanism of insulin receptor kinase inhibition in non-insulin-dependent diabetes mellitus patients. Phosphorylation of serine 1327 or threonine 1348 is unaltered

The tyrosine kinase activity of insulin receptor isolated from the skeletal muscle of NIDDM patients has previously been found to be decreased compared with the activity of receptor from nondiabetic subjects but the mechanism underlying this defect is unknown. Phosphorylation of receptor serine/threonine residues has been proposed to exert an inhibitory influence on receptor tyrosine kinase activity and Ser 1327 and Thr 1348 have been identified as specific sites of phosphorylation in the insulin receptor COOH terminal domain. To address the potential negative regulatory role of phosphorylation of these residues in vivo, we assessed the extent of phosphorylation of each site in insulin receptor isolated from the skeletal muscle of 12 NIDDM patients and 13 nondiabetic, control subjects. Phosphorylation of Ser 1327 and Thr 1348 was determined using antibodies that specifically recognize insulin receptor phosphorylated at these sites. In addition, a phosphotyrosine-specific antibody was used to monitor receptor tyrosine phosphorylation. The extent of insulin-induced tyrosine autophosphorylation was decreased in receptor isolated from diabetic versus nondiabetic muscle, thus confirming earlier reports. In contrast, there was no significant difference in the extent of phosphorylation of either Ser 1327 or Thr 1348 in receptor isolated from diabetic or nondiabetic muscle as assessed by immunoprecipitation (Ser 1327: 5.6 +/- 1.6% diabetics vs. 4.7 +/- 2.0% control; Thr 1348: 3.8 +/- 1.0% diabetics vs. 3.2 +/- 1.2% control). Moreover, within each group there was no correlation between the level of tyrosine kinase activity and the extent of serine/threonine phosphorylation. It is concluded that the stoichiometry of serine/threonine phosphorylation of insulin receptor in vivo is low, and that increased phosphorylation of Ser 1327 or Thr 1348 is not responsible for the decreased insulin receptor tyrosine kinase activity observed in the skeletal muscle of NIDDM patients.