Biomedical subjects

F H Nystrom

Publications and source records attributed to F H Nystrom.

6 recordsLinked to original sources

PubMed2001

Insulin stimulates increased catalytic activity of phosphoinositide-dependent kinase-1 by a phosphorylation-dependent mechanism.

Phosphoinositide-dependent kinase-1 (PDK-1) is a serine-threonine kinase downstream from PI 3-kinase that phosphorylates and activates other important kinases such as Akt that are essential for cell survival and metabolism. Previous reports have suggested that PDK-1 has constitutive catalytic activity that is not regulated by stimulation of cells with growth factors. We now show that insulin stimulation of NIH-3T3(IR) cells or rat adipose cells may significantly increase the intrinsic catalytic activity of PDK-1. Insulin treatment of NIH-3T3(IR) fibroblasts overexpressing PDK-1 increased both phosphorylation of recombinant PDK-1 in intact cells and PDK-1 kinase activity in an immune-complex kinase assay. Insulin stimulation of rat adipose cells also increased catalytic activity of endogenous PDK-1 immunoprecipitated from the cells. Both insulin-stimulated phosphorylation and activity of PDK-1 were inhibited by wortmannin and reversed by treatment with the phosphatase PP-2A. A mutant PDK-1 with a disrupted PH domain (W538L) did not undergo phosphorylation or demonstrate increased kinase activity in response to insulin stimulation. Similarly, a PDK-1 phosphorylation site point mutant (S244A) had no increase in kinase activity in response to insulin stimulation. Thus, the insulin-stimulated increase in PDK-1 catalytic activity may involve PI 3-kinase- and phosphorylation-dependent mechanisms. We conclude that the basal constitutive catalytic activity of PDK-1 in NIH-3T3(IR) cells and rat adipose cells can be significantly increased upon insulin stimulation.

3-Phosphoinositide-Dependent Protein Kinases↗

PubMed2001

Reduction of ACE activity is insufficient to decrease microalbuminuria in normotensive patients with type 1 diabetes.

OBJECTIVE: To study whether administration of 1.25 and 5.0 mg ramipril daily, compared with placebo treatment, reduces the urinary albumin excretion rate (UAER) in normotensive patients with type 1 diabetes. RESEARCH DESIGN AND METHODS: Ramipril was administered double blind at two different doses (1.25 [n = 19] and 5.0 mg [n = 18]), and compared with placebo (n = 18) after a single-blind placebo period of 1-4 weeks. The patients (total, n = 55; women, n = 14) were followed for 2 years. To document an effect on the renin-angiotensin system, ACE activity and plasma-renin activity (PRA) were measured. In addition, 24-h ambulatory blood pressure (BP) was recorded at baseline and repeated after 1 and 2 years using a Spacelab 90207 ambulatory BP recording device (Spacelab, Redmont, CA). RESULTS: Both doses of ramipril were sufficient to reduce ACE activity and to increase PRA significantly as compared with placebo (P < 0.05 for both). On the other hand, neither ambulatory nor clinic BP was affected by either dose of ramipril compared with the placebo group. There was no progression of UAER in the placebo group during the 2 years of the study. Analysis of covariance showed no differences in UAER between the three treatment groups at year 1 (P = 0.94) or year 2 (P = 0.97), after adjusting for baseline. Furthermore, there were no statistically significant changes from baseline UAER within any of the three treatment groups. CONCLUSIONS: Treatment with ramipril did not affect microalbuminuria or clinic or ambulatory BP in this study. On the basis of the present study, we question the clinical use of ACE inhibitors in stably normotensive patients with type 1 diabetes and microalbuminuria in whom a concomitant reduction in BP is not demonstrated.

Albuminuria↗

PubMed2000

Roles for insulin receptor, PI3-kinase, and Akt in insulin-signaling pathways related to production of nitric oxide in human vascular endothelial cells.

BACKGROUND: Previously, we demonstrated that insulin stimulates production of nitric oxide (NO) in endothelial cells. However, specific insulin-signaling pathways mediating production of NO have not been elucidated. METHODS AND RESULTS: We developed methods for transfection of human umbilical vein endothelial cells (HUVECs) and direct measurement of NO to begin defining insulin-signaling pathways related to NO production. HUVECs were cotransfected with enhanced Green Fluorescent Protein (eGFP) and another gene of interest. Transfection efficiencies >95% were obtained by selecting cells expressing eGFP. Overexpression of insulin receptors in HUVECs resulted in an approximately 3-fold increase in production of NO in response to insulin. In contrast, HUVECs overexpressing a tyrosine kinase-deficient mutant insulin receptor had a dose-response curve similar to that of control cells. Overexpression of inhibitory mutants of either phosphatidylinositol 3-kinase (PI3K) or Akt resulted in nearly complete inhibition of insulin-stimulated production of NO. Overexpression of an inhibitory mutant of Ras had a much smaller effect. CONCLUSIONS: Receptor kinase activity is necessary to mediate production of NO through the insulin receptor. Both PI3K and Akt contribute importantly to this process, whereas the contribution of Ras is small.

Cells, Cultured↗

PubMed2000

The renin-angiotensin-aldosterone system is suppressed in adults with Type 1 diabetes.

Poor glycaemic control and high blood pressure are two important risk factors for the development of retinopathy and nephropathy in Type 1 diabetes. The renin-angiotensin-aldosterone system (RAAS) may be involved in this process, since treatment with angiotensin-converting enzyme (ACE) inhibitors postpones the development of these complications. We investigated whether plasma renin activity (PRA), plasma angiotensin II (Ang II) and atrial natriuretic peptide (ANP) differed in Type 1 diabetic patients compared with healthy controls. We recruited 80 patients with Type 1 diabetes of more than 10 years' duration and 75 age-matched controls. We found that PRA and Ang II concentrations were significantly lower in patients than in the controls. The levels of ANP, on the other hand, were higher in patients than in controls. PRA correlated negatively to the mean value of HbA(1c) during the previous five years. PRA and Ang II were significantly lower in patients with mean HbA(1c) >8.4% compared with those with mean HbA(1c) <7.2%. In summary, we found patients with Type 1 diabetes to have RAAS suppression and increased ANP levels, suggesting a state of fluid retention.

Adult↗

PubMed1999

Insulin signalling: metabolic pathways and mechanisms for specificity.

Biological actions of insulin are mediated by the insulin receptor, a member of a large family of receptor tyrosine kinases (RTK). Signal transduction by the insulin receptor follows a paradigm for RTK signalling. Many intracellular signalling molecules contain multiple modular domains that mediate protein-protein interactions and participate in the formation of signalling complexes. Phosphorylation cascades are also a prominent feature of RTK signalling. Distal pathways are difficult to dissect because branching paths emerge from downstream effectors and several upstream inputs converge upon single branch points. Thus, insulin action is determined by complicated signalling networks rather than simple linear pathways. Interestingly, many signalling molecules downstream from the insulin receptor are also activated by a plethora of RTKs. Therefore, mechanisms that generate specificity are required. In this review we discuss recent advances in the elucidation of specific metabolic insulin signalling pathways related to glucose transport, one of the most distinctive biological actions of insulin. We also present examples of potential mechanisms underlying specificity in insulin signalling including interactions between multiple branching pathways, subcellular compartmentalization, tissue-specific expression of key effectors and modulation of signal frequency and amplitude.

Animals↗

PubMed1999

Caveolin-1 interacts with the insulin receptor and can differentially modulate insulin signaling in transfected Cos-7 cells and rat adipose cells.

Caveolae may function as microdomains for signaling that help to determine specific biological actions mediated by the insulin receptor (IR). Caveolin-1, a major component of caveolae, contains a scaffolding domain (SD) that binds to a caveolin-1 binding motif in the kinase domain of the IR in vitro. To investigate the potential role of caveolin-1 in insulin signaling we overexpressed wild-type (Cav-WT) or mutant (Cav-Mut; F92A/V94A in SD) caveolin-1 in either Cos-7 cells cotransfected with IR or rat adipose cells (low and high levels of endogenous caveolin-1, respectively). Cav-WT coimmunoprecipitated with the IR to a much greater extent than Cav-Mut, suggesting that the SD is important for interactions between caveolin-1 and the IR in intact cells. We also constructed several IR mutants with a disrupted caveolin-1 binding motif and found that these mutants were poorly expressed and did not undergo autophosphorylation. Interestingly, overexpression of Cav-WT in Cos-7 cells significantly enhanced insulin-stimulated phosphorylation of Elk-1 (a mitogen-activated protein kinase-dependent pathway) while overexpression of Cav-Mut was without effect. In contrast, in adipose cells, overexpression of either Cav-WT or Cav-Mut did not affect insulin-stimulated phosphorylation of a cotransfected ERK2 (but did significantly inhibit basal phosphorylation of ERK2). Furthermore, we also observed a small inhibition of insulin-stimulated translocation of GLUT4 when either Cav-WT or Cav-Mut was overexpressed in adipose cells. Thus, interaction of caveolin-1 with IRs may differentially modulate insulin signaling to enhance insulin action in Cos-7 cells but inhibit insulin's effects in adipose cells.

Adipocytes↗