Insulin-like growth factors augment steroid production and expression of steroidogenic enzymes in human fetal adrenal cortical cells: implications for adrenal androgen regulation

The fetal zone is a unique adrenal cortical compartment that exists only during fetal life in humans and higher primates and produces large amounts of the adrenal androgen dehydroepiandrosterone sulfate (DHEA-S). Growth of the fetal zone is primarily regulated by ACTH, the actions of which are mediated in part by locally produced autocrine/paracrine growth factors. We previously demonstrated that one of these growth factors, insulin-like growth factor II (IGF-II), is mitogenic for cultured fetal zone cells and is produced in high abundance by these cells in response to ACTH. In the present study, we determined whether IGF-II also modulates the differentiated function of fetal zone cells. We examined the effects of recombinant human IGF-II and the closely related peptide, IGF-I, on 1) basal and agonist-stimulated [ACTH-(1-24), forskolin, or 8-bromo-cAMP] cortisol and DHEA-S production, 2) basal and ACTH-stimulated steady state abundance of messenger ribonucleic acids (mRNAs) encoding the steroidogenic enzymes cytochrome P450 side-chain cleavage (P450scc) and cytochrome P450 17alpha-hydroxylase/17,20-lyase (P450c17), and 3) basal and ACTH-stimulated steady state abundance of mRNA encoding the ACTH receptor. Basal cortisol (23.93 +/- 1.20 pmol/10(5) cells x 24 h) and DHEA-S (548.87 +/- 43.17 pmol/10(5) cells x 24 h) productions were significantly (P < 0.05) increased by IGF-I (2.3- and 1.8-fold, respectively) and IGF-II (2.8- and 1.8-fold, respectively). As expected, ACTH, forskolin, and cAMP markedly increased the production of cortisol by 26-, 10-, and 13-fold, respectively, and that of DHEA-S by 5.4-, 4.6-, and 5.5-fold, respectively, compared with basal levels. IGF-II (100 ng/mL) significantly (P < 0.001) increased ACTH-, forskolin-, and cAMP-stimulated production of cortisol by 2.4-, 4.3-, and 3.2-fold, respectively, and that of DHEA-S by 1.4, 1.6-, and 1.4-fold, respectively. IGF-I (100 ng/mL) had similar effects as IGF-II and significantly (P < 0.001) increased ACTH-, forskolin-, and cAMP-stimulated production of cortisol by 2.8-, 3.9-, and 3.1-fold, respectively, and that of DHEA-S by 1.3-, 1.6-, and 1.4-fold, respectively. The similar potencies of IGF-I and IGF-II suggest that the actions of these factors were mediated via a common receptor, most likely the type I IGF receptor. The effects of IGF-II on ACTH-stimulated steroid production were dose-dependent (EC50, 0.5-1.0 nmol/L), and IGF-II markedly increased the steroidogenic responsiveness of fetal zone cells to ACTH. With respect to cortisol production, IGF-II shifted the ACTH dose-response curve to the left by 1 log10 order of magnitude. IGF-II also increased ACTH-stimulated abundance of mRNA encoding P450scc (1.9-fold) and P450c17 (2.2-fold). Basal expression of P450scc was not affected by IGF-II. In contrast, basal expression of P450c17 was increased 2.2-fold by IGF-II and IGF-I in a dose-responsive fashion. Neither IGF-I nor IGF-II affected basal or ACTH-stimulated abundance of mRNA encoding the ACTH receptor, suggesting that the increase in ACTH responsiveness was not mediated by an increase in ACTH-binding capacity. Taken together, these data indicate that activation of the type I IGF receptor increases ACTH responsiveness in fetal zone cells by modulating ACTH signal transduction at some point distal to ACTH receptor activation. These data also indicate that locally produced IGF-II modulates fetal adrenal cortical cell function by increasing responsiveness to ACTH and possibly (based on its direct stimulation of P450c17 expression) augmenting the potential for adrenal androgen synthesis. Thus, activation of the type I IGF receptor on adrenal cortical cells may play a pivotal role in adrenal androgen production, both physiologically in utero and at adrenarche, and in pathophysiological conditions ofhyperandrogenemia, such as the polycystic ovary syndrome.

Protein-tyrosine phosphatases PTP1B and syp are modulators of insulin-stimulated translocation of GLUT4 in transfected rat adipose cells

The protein-tyrosine phosphatases PTP1B and Syp have both been implicated as modulators of the mitogenic actions of insulin. However, the roles of these protein-tyrosine phosphatases in the metabolic actions of insulin are not well characterized. In this study, we directly assessed the ability of PTP1B and Syp to modulate insulin-stimulated translocation of the insulin-responsive glucose transporter GLUT4 in a physiologically relevant insulin target cell. Primary cultures of rat adipose cells were transiently transfected with either wild-type PTP1B (PTP1B-WT), wild-type Syp (Syp-WT), or the catalytically inactive mutants PTP1B-C/S or Syp-C/S. The effects of overexpression of these constructs on insulin-stimulated translocation of a co-transfected epitope-tagged GLUT4 were studied. Cells overexpressing either PTP1B-C/S or Syp-WT had insulin dose-response curves similar to those obtained with control cells expressing only epitope-tagged GLUT4. In contrast, for cells overexpressing PTP1B-WT the level of GLUT4 on the cell surface at each insulin dose (ranging from 0 to 60 nM) was significantly lower than that observed in the control cells. Interestingly, cells overexpressing the dominant inhibitory mutant Syp-C/S also had a small but statistically significant impairment in insulin responsiveness. At a maximally stimulating concentration of insulin (60 nM), cell surface epitope-tagged GLUT4 was approximately 20% less than that of the control cells. It is possible that effects from high level overexpression of Syp and PTP1B constructs may not reflect what occurs under physiological conditions. Nevertheless, our data raise the possibility that PTP1B may be a negative regulator of insulin-stimulated glucose transport, while Syp may have a small role as a positive mediator of the metabolic actions of insulin.

Effect of influenza immunization on immunologic and virologic characteristics of pediatric patients infected with human immunodeficiency virus

OBJECTIVES

We evaluated the responses of HIV-infected children to a single dose of split-virus influenza vaccine and the relationship to viral load and other characteristics.

METHODS

Fifty-three HIV-infected children ages 1.8 to 13.2 years were given influenza vaccine for the 1994 to 1995 influenza season (Wyeth-Ayerst: A/Texas H1N1, A/Shangdong H3N2 and B/Panama). Immunologic and virologic factors were assessed at the time of and 2 to 10 weeks after immunization.

RESULTS

The differences between pre- and postimmunization CD4+ counts, CD4+:CD8+ ratios and viral load were not significant. Thirty-one of 53 children (58.4%) had a > 2-fold increase and 16 of 53 (30%) had a 4-fold rise in their postimmunization antibody titers for at least one component of the vaccine. Influenza immunization in the 1993 to 1994 flu season and administration of intravenous immunoglobulin around the time of immunization was not associated with immune response to the vaccine. Factors that were negatively associated with antibody response included increased time between samples (P = 0.004) and decreased preimmunization CD4+:CD8+ ratio (P = 0.02).

CONCLUSIONS

Influenza immunization in this population is safe, and a positive antibody response to influenza immunization is not associated with significant clinical events or change in HIV-1 plasma viral burden.

Ventilatory control in a primitive fish: signal conditioning via non-linear O2 affinity

Gas exchange in the gills of the air-breathing fish Amia calva was modelled to determine how the gills modify fluctuations in venous P O2. These fluctuations form the physiological signal for aerial ventilation in these fish. This study was performed to examine the signal conditioning role that the gills may play in the control system that regulates P O2. The model incorporated a non-linear Hb-O2 affinity relationship. Fluctuations in venous P O2 were modelled as sinusoids, covering a range of frequencies and amplitudes. Mean venous P O2 ranged from normoxic to hypoxic values. Over a broad range of parameters the gills amplify fluctuations in venous P O2 during transit to the arterial side. It was also observed that aquatic hypoxia reduces the effectiveness of the gills in maximizing arterial P O2, while increases in venous P O2 increase the effectiveness of the gills in the face of similar blood-water P O2 gradients. Each of these performance features is a consequence of the sigmoid Hb-O2 affinity relationship.

Measles immunity in HIV-infected children

In a retrospective study, sera from 84 children of human immunodeficiency virus (HIV)-seropositive mothers (35 HIV-infected and 49 uninfected children) with a known date of receipt of measles, mumps, and rubella vaccine were tested for antibody to measles vaccine by an indirect enzyme immunoassay (EIA) method and/or microneutralization (NEUT). At the time of last measurement, 21/35 (60.0%) HIV-infected children remained seropositive by either EIA or NEUT. Forty seven of forty-nine (95.9%) uninfected children had evidence of measles antibody. Six HIV-infected children had a documented loss of antibody over time. The majority of HIV-infected children had antibody to measles vaccine virus, which in some cases decreased over time.

De novo methylation of an MHC class I transgene following transformation with human adenoviruses is not correlated with its altered expression

The biological importance of class I histocompatibility antigens in a large variety of immune mechanisms is widely recognized, and their role in tumor rejection has been proven in several experimental tumor systems. Reduced expression of class I antigens, which is correlated with enhanced tumorigenicity, was shown in these systems to be mainly the result of transcriptional down-regulation. Mouse embryonal fibroblasts expressing H-2 antigens and the product of a miniature swine class I transgene, transformed by adenovirus 12, exhibit low levels of all class I antigens on the cell surface. Half of the cell lines demonstrate a suppressed level of class I mRNAs. Cell lines derived from transformation with the early region of adenovirus 5 express a high level of class I antigens. DNAs from adenovirus-transformed cells are extensively hypermethylated both in the 5' and the coding regions of the transgene compared to DNAs from immortalized cell lines and primary embryonal fibroblasts. Nevertheless, hypermethylation of these sequences is not correlated with mRNA level or cell-surface expression of the transgene product. Treatment of the transformed cells with high concentration of 5-azacytidine (5 Aza-C) induced merely a minor enhancement in the expression of class I mRNAs and class I antigens. Thus, this system is a perfect example of where viral transformation is associated with induced methylation of a class I gene, but hypermethylation does not affect its expression. The role of de novo methylation of genes in this system might be associated with transformation, or generation of mutations in CpG-rich sequences.

Prospects for childhood immunization in the next decade

Prospects for vaccine research, development, and use over the next decade are extraordinarily optimistic. Innovative investigative programs promise new vaccines with reduced numbers of injections, combinations of multiple antigens, and confinement of administration to the early weeks or months of life. Enhanced attention to the infrastructure and support of immunization programs should rapidly augment coverage to more than 90% of the US infant population in the first 2 years of life with all the recommended vaccines. Programs of the WHO and CVI should extend protection from morbidity and mortality of diseases preventable with vaccine to children of all nations. Adjustments and realignments of the Vaccine Injury Compensation Program should reduce to realistic dimensions the finances of benefits for children who suffer the rare, true adverse responses to required immunizations. In order to maintain familiarity and leadership in childhood immunization, pediatricians will need to maintain careful attention to and familiarity with all these emerging developments.