Suppressors of cytokine signaling-1 and -6 associate with and inhibit the insulin receptor. A potential mechanism for cytokine-mediated insulin resistance

Insulin resistance contributes to a number of metabolic disorders, including type II diabetes, hypertension, and atherosclerosis. Cytokines, such as tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6, and hormones, such as growth hormone, are known to cause insulin resistance, but the mechanisms by which they inhibit the cellular response to insulin have not been elucidated. One mechanism by which these agents could cause insulin resistance is by inducing the expression of cellular proteins that inhibit insulin receptor (IR) signaling. Suppressors of cytokine signaling (SOCS) proteins are negative regulators of cytokine signaling pathways, the expression of which is regulated by certain cytokines. SOCS proteins are therefore attractive candidates as mediators of cytokine-induced insulin resistance. We have found that SOCS-1 and SOCS-6 interact with the IR when expressed in human hepatoma cells (HepG2) or in rat hepatoma cells overexpressing the human IR. In SOCS-1-expressing cells, insulin treatment increases the extent of interaction with the IR, whereas in SOCS-6-expressing cells the association with the IR appears to require insulin treatment. SOCS-1 and SOCS-6 do not inhibit insulin-dependent IR autophosphorylation, but both proteins inhibit insulin-dependent activation of ERK1/2 and protein kinase B in vivo and IR-directed phosphorylation of IRS-1 in vitro. These results suggest that SOCS proteins may be inhibitors of IR signaling and could mediate cytokine-induced insulin resistance and contribute to the pathogenesis of type II diabetes.

AIB1 enhances estrogen-dependent induction of cyclin D1 expression

AIB1 was isolated as a gene amplified in breast cancer and encodes a protein that acts as a steroid receptor coactivator. The role of steroid receptor coactivators such as AIB1 in breast cancer development is not clear. It is possible that AIB1 cooperates with estrogen receptor alpha in regulating estrogen-dependent cell proliferation. Ectopic expression of the estrogen receptor alpha in different cell lines does not confer estrogen-induced proliferation. This inability of the estrogen receptor to drive proliferation has been recently correlated with a lack of estrogen-dependent cyclin D1 expression in cells engineered to express the estrogen receptor. In this study, we evaluated whether high levels of AIB1 enable the estrogen receptor to direct the transcription of cyclin D1. We show here that AIB1 and other steroid receptor coactivators can enhance the functional interaction of the estrogen receptor with the cyclin D1 promoter. Increases of AIB1 levels in breast cancer cells by amplification and/or overexpression may represent one way to confer estrogen-dependent mitogenic stimulation to breast cancer cells.

Carotid intima-media thickness and the association with cardiovascular risk factors in the elderly

OBJECTIVE

To investigate the association of carotid arterial intima-media thickness (IMT) with principal cardiovascular risk factors in the elderly.

METHODS

Carotid arterial IMT was measured by high resolution B mode ultrasound in 94 elderly subjects (old-aged group), and compared with subjects aged < 60 (middle-aged group).

RESULTS

In comparison with the middle-aged group, the prevalence of coronary heart disease, cerebral vascular disease, hypertension and diabetes mellitus was significantly higher, and serum cholesterol and systolic blood pressure were also significantly higher in old-aged group. Although there was no obvious difference in IMT between the two groups, carotid plaque and carotid wall thickening were more frequently found in old-aged group. Age, systolic blood pressure and serum cholesterol were shown as the independent determinants for carotid IMT in the total participants, whereas no such independent relation was found in old-aged group.

CONCLUSION

Age is the major risk factor for carotid atherosclerosis in the elderly. In other words, the occurrence of carotid atherosclerosis is the result of advancing age combined with the effect of multiple cardiovascular risk factors.

Cofactor dynamics and sufficiency in estrogen receptor-regulated transcription

Many cofactors bind the hormone-activated estrogen receptor (ER), yet the specific regulators of endogenous ER-mediated gene transcription are unknown. Using chromatin immunoprecipitation (ChIP), we find that ER and a number of coactivators rapidly associate with estrogen responsive promoters following estrogen treatment in a cyclic fashion that is not predicted by current models of hormone activation. Cycles of ER complex assembly are followed by transcription. In contrast, the anti-estrogen tamoxifen (TAM) recruits corepressors but not coactivators. Using a genetic approach, we show that recruitment of the p160 class of coactivators is sufficient for gene activation and for the growth stimulatory actions of estrogen in breast cancer supporting a model in which ER cofactors play unique roles in estrogen signaling.

BRG-1 is recruited to estrogen-responsive promoters and cooperates with factors involved in histone acetylation

Several factors that mediate activation by nuclear receptors also modify the chemical and structural composition of chromatin. Prominent in this diverse group is the steroid receptor coactivator 1 (SRC-1) family, which interact with agonist-bound nuclear receptors, thereby coupling them to multifunctional transcriptional coregulators such as CREB-binding protein (CBP), p300, and PCAF, all of which have potent histone acetyltransferase activity. Additionally factors including the Brahma-related gene 1 (BRG-1) that are involved in the structural remodeling of chromatin also mediate hormone-dependent transcriptional activation by nuclear receptors. Here, we provide evidence that these two distinct mechanisms of coactivation may operate in a collaborative manner. We demonstrate that transcriptional activation by the estrogen receptor (ER) requires functional BRG-1 and that the coactivation of estrogen signaling by either SRC-1 or CBP is BRG-1 dependent. We find that in response to estrogen, ER recruits BRG-1, thereby targeting BRG-1 to the promoters of estrogen-responsive genes in a manner that occurs simultaneous to histone acetylation. Finally, we demonstrate that BRG-1-mediated coactivation of ER signaling is regulated by the state of histone acetylation within a cell. Inhibition of histone deacetylation by trichostatin A dramatically increases BRG-1-mediated coactivation of ER signaling, and this increase is reversed by overexpression of histone deacetylase 1. These studies support a critical role for BRG-1 in ER action in which estrogen stimulates an ER-BRG-1 association coupling BRG-1 to regions of chromatin at the sites of estrogen-responsive promoters and promotes the activity of other recruited factors that alter the acetylation state of chromatin.

The induction and activation of STAT1 by all-trans-retinoic acid are mediated by RAR beta signaling pathways in breast cancer cells

Retinoic acid receptor-beta (RAR beta) and signal transducer and activator of transcription 1 (STAT1) are important mediators of the antiproliferative and apoptotic actions of retinoids and cytokines/growth factors, respectively. Expression of both RAR beta and STAT1 is lost in most breast cancer cell lines but it can be induced by retinoids in estrogen receptor-positive cells. We investigated a possible functional connection between these two mediators and present evidence supporting RAR beta as a tumor suppressor. First, by using different receptor-selective retinoids, we demonstrated that RAR beta induction in MCF-7 cells by all-trans-retinoic acid (atRA) was associated with the activation of STAT1 gene transcription. The direct involvement of RAR beta in atRA-induced STAT1 gene activation was further demonstrated by showing that transfection with an anti-sense RAR beta construct blocked atRA-induced STAT1 expression in MCF-7 cells whereas introduction of a sense-RAR beta construct resulted in STAT1 induction by atRA in MDA-MB 231 cells. In addition, we showed that STAT1 was phosphorylated/activated under atRA treatment of MCF-7 cells; this process required the involvement of RAR beta and protein synthesis. STAT1 phosphorylation/activation was accompanied by increased tyrosine kinase activity that was not due to the activation of JAK1, JAK2 or Tyk 2, suggesting the possible involvement of an unidentified tyrosine kinase.

Signal relay by retinoic acid receptors alpha and beta in the retinoic acid-induced expression of insulin-like growth factor-binding protein-3 in breast cancer cells

Neither retinoic acid receptor-beta (RARbeta) nor insulin-like growth factor-binding protein-3 (IGFBP-3) is expressed in breast cancer cell line MCF-7. The expression of both proteins can be induced in response to all-trans-retinoic acid (atRA). By using an RARalpha-selective antagonist (Ro 41-5253), we demonstrated that RARbeta expression was induced by atRA through an RARalpha-dependent signaling pathway and that RARbeta induction was correlated with IGFBP-3 induction. However, MCF-7 cells transfected with sense RARbeta cDNA expressed IGFBP-3 even in the presence of the RARalpha-selective antagonist Ro 41-5253. On the other hand, antisense RARbeta cDNA transfection of MCF-7 cells blocked atRA-induced IGFBP-3 expression, indicating that RARbeta is directly involved in the mediation of IGFBP-3 induction by atRA. Induction of IGFBP-3 expression by atRA occurs at the transcriptional level, as measured by nuclear run-on assays. Finally, we showed that atRA-induced IGFBP-3 is functionally active in modulating the growth-promoting effect of IGF-I. These experiments indicate that RARalpha and RARbeta, both individually and together, are important in mammary gland homeostasis and breast cancer development. By linking IGFBP-3 to RARbeta, our experiments define the signal intersection between the retinoid and IGF systems in cell growth regulation and explain why loss of RARbeta might be critical in breast cancer carcinogenesis/progression.

Castration differentially alters [3H]nisoxetine binding to norepinephrine uptake sites in olfactory bulb and frontal cortex of male rats

In the present study, [3H]nisoxetine binding to norepinephrine (NE) uptake sites and [3H]norepinephrine uptake were investigated within olfactory bulb (OB) and frontal cortex homogenates from intact and castrated male rats. Statistically significant reductions in the number of [3H]nisoxetine binding sites (Bmax) were found in OB from the castrates, while significantly increased Bmax values were obtained in the frontal cortex. Castration also significantly altered the affinity (Kd) of [3H]nisoxetine binding in the frontal cortex, but not in the OB. Assessment of [3H]norepinephrine uptake showed that in neither brain regions were there any statistically significant differences in Km nor Vmax between the castrated and intact male rats, indicating that the basal uptake process is not changed following castration in either of these brain areas. These results demonstrate the differential effects of castration upon [3H]nisoxetine binding sites between the OB and frontal cortex. Such findings provide new evidence for one of the mechanisms by which androgens may modulate central noradrenergic activity.

c-Myc is a major mediator of the synergistic growth inhibitory effects of retinoic acid and interferon in breast cancer cells

The molecular signaling events involved in the inhibition of breast cancer cell growth by retinoic acid and interferon-alpha were investigated. All-trans-retinoic acid and interferon-alpha acted synergistically to inhibit growth of both the estrogen receptor-positive breast cancer cell line MCF-7 and the estrogen receptor-negative line BT-20. In MCF-7 cells, all-trans-retinoic acid potentiated the effects of interferon-alpha by up-regulating the expression of the RNA-dependent protein kinase (PKR). Consequently, the synergism between all-trans-retinoic acid and interferon-alpha down-regulated the expression of c-Myc, but not its functional partner, Max. Transfection of MCF-7 cells with a dominant-negative mutant of PKR relieved c-Myc down-regulation and cell growth inhibition, indicating that PKR is directly involved in c-Myc down-regulation and that c-Myc down-regulation is responsible for the inhibition of cell growth. Corresponding with c-Myc down-regulation, c-Myc.Max heterodimers bound to their consensus DNA sequence were undetectable in cells treated with all-trans-retinoic acid and interferon-alpha, indicating diminished c-Myc functionality. When c-Myc was overexpressed ectopically via a c-Myc expression vector, MCF-7 cells became resistant to growth inhibition by all-trans-retinoic acid plus interferon-alpha. These experiments define the following pathway as a major pathway in the synergistic growth inhibition of MCF-7 cells by all-trans-retinoic acid plus interferon-alpha: all-trans-retinoic acid + interferon-alpha --> upward arrow double-stranded RNA-dependent protein kinase --> downward arrow c-Myc --> cell growth inhibition.

Castration reduces olfactory bulb norepinephrine transporter function as indicated by responses to noradrenergic uptake blockers

It has been demonstrated that castration alters the functioning of the olfactory bulb (OB)-norepinephrine (NE) system. In the present experiment, we examined one of the mechanisms by which castration modulates the OB-NE system by comparing NE uptake activity between intact and castrated male rats as studied using an in vitro superfusion technique. To accomplish this goal, NE output from the OB of intact and castrated male rats in response to infusion with two different drugs which alter NE uptake functions, tomoxetine and talsupram, were tested. Overall, NE outputs in response to tomoxetine were significantly higher in the castrated than in intact rats and both groups were significantly greater than non-infused controls. For the talsupram infusion group, NE outputs from the castrated, but not intact rats, were significantly greater than controls. No statistically significant differences were detected between the castrated and intact rats. These results demonstrate that castration alters the NE uptake activities in response to these noradrenergic uptake blockers and suggest that one mechanism by which castration alters OB-NE functioning is through reducing the uptake activity of NE within the OB. Such findings have important implications for olfactory-based learning and memory/recognition processes which are believed to involve the OB-NE system and are altered following castration.

[Effect of different training time and loads on the metabolism of carbohydrate, fat and protein]

Twenty-five athletes were selected to receive three kinds of loads (endurance, strength and sprint training) at the same training time, as well as to receive the same kind of load at different time (morning, am. pm), then the tricarboxylic acid (TCA) cycle products, free fatty acids (FFA), urea nitrogen, creatinine and free amino acids contents in their serum were measured. The results showed that at the same training time, different loads led to different physiological effects, while the same kind of exercise training resulted in more protein catabolism in p.m. than in the morning or a.m. Endurance or training in the morning had considerable influence on the levels of TCA cycle products and FFA components. Training in p. m. may be favourable to improving the quality of the sports of speed and strength.

[Enzynology of infected part of red skin ginseng]

By means of polyacrylaminde gel eletrothoresis and thin layer scanning, the paper semi-quantitatively studies some relation between component and activity of isoenayme of Ginseng infecting red skin desease. The results show activity of esterase increases 100% than that of normal Ginseng; activity of polyphenol oxidase increases 60-30% and represent new isoenzyme bands in the early infection in juxtapose transolant experiment.

Approaches and reconstruction in skull base operation

OBJECTIVE

To design convenient lateronasal and infrafrontal approaches or lateronasal subvolution approach to radically resect skull base tumors involving cranial cavity.

METHODS

From 1987 through 1994, 22 patients with malignant tumors, 6 with benign tumors, one with a giant sphenoid sinus cyst and one with intranasal meningoencephalocele underwent the operation. Twenty-three cases had anterocranial fossa involved; 4, midcranial fossa; 2, anteromedial cranial fossa; and 1 case, posteromedial cranial fossa. Among the patients with malignant tumors, 11 underwent expansive maxillectomy and 10 had orbital contents resected. The intracranial approaches through lateronasal and infrafront (21 cases), nasal columella lateral subvolution (3 cases) and other approaches were used.

RESULTS

The reconstruction of bony skull base defect in excess of 3.00 cm x 3.00 cm with total front musculocutaneous flap (8 cases), galeal and pericranial flap (5 cases) or other tissues (3 cases) has effectively prevented meningoencephalocele. Twelve cases had the dura resected in a range of 2.00 cm x 2.00 cm to 7.00 cm x 6.00 cm. Reconstruction of the dura defect with autofascia lata in 9 cases and other tissues in 3 cases effectively prevented the cerebrospinal fluid leak. Eight of 22 (36.4%) patients with malignant tumors have been alive and free of disease for 3-7 years after the operation. Six patients with benign tumors, one patient with giant sphenoid sinus cyst and one with meningoencephalocele were cured with this reconstructing method.

CONCLUSIONS

Frontal musculocutaneous and pericranial flaps have advantages over free bone because of easy surviving and easy operating without occurrence of osteonecrosis and exclusive reaction.