Search PubMed⌕ Search

Biomedical subjects

D Le Roith

Publications and source records attributed to D Le Roith.

At least 37 records · Page 2Linked to original sources
PubMed1998

Insulin-like growth factor-I inhibits the stress-activated protein kinase/c-Jun N-terminal kinase.

The pathways involved in the cellular responses to the insulin-like growth factors (IGFs) are numerous and vary according to cell type. Following activation of the IGF-I receptor, the mitogen-activated protein kinase and phosphatidylinositide 3'-kinase (PI3'K) pathways are activated and result in cellular proliferation and inhibition of apoptosis. In this study, we analyzed the IGF-I effect on the stress-activated protein kinase/c-Jun N-terminal kinase (JNK) activity using human embryonic kidney 293 cells, 293 cells transiently expressing hemagglutinin-JNK, and 293 cells stably expressing a hemagglutinin-JNK transgene. In all cell types, endogenous or transfected JNK activity was strongly stimulated by anisomycin or tumor necrosis factor-alpha, and 10 nM IGF-I pretreatment suppressed the induced JNK activity. To determine whether the effect of IGF-I on JNK activity involves the mitogen-activated protein kinase or PI3'K pathway, we used the specific MEK1 inhibitor PD098059 and the PI3'K inhibitor LY 294002. PD098059 did not alter the IGF-I suppressive effect on stressor-induced JNK activity, but LY 294002 suppressed the IGF-I effect. Moreover, in transiently transfected parental 293 cells expressing dominant-negative Akt, anisomycin-increased JNK activity was not suppressed by pretreatment with IGF-I. Our results demonstrate that the action of IGF-I on JNK in these cells is via PI3'K and Akt.

Anisomycin↗
PubMed1997

The proto-oncogene Crk-II enhances apoptosis by a Ras-dependent, Raf-1/MAP kinase-independent pathway.

Human embryonic kidney 293 cells and 293 cells overexpressing different amounts of the adaptor protein Crk-II (ranging from 3- to 10-fold higher levels than the parental cell line) were examined for their ability to undergo apoptosis when maintained in control and serum-free (SF) medium. Parental 293 cells undergo apoptosis only when deprived of serum for prolonged periods of time (24-48 h). On the other hand, 293 cells overexpressing different levels of Crk-II present detectable levels of apoptosis as measured by DNA fragmentation when grown in control medium, with a marked increase when they are deprived of serum for 12-48 h. To determine the pathways involved in Crk-II-induced apoptosis, Crk-II overexpressing cells were transiently transfected with a dominant-negative Ras construct (N17-Ras). Compared to cells transfected with control vectors, the cells overexpressing N17-Ras presented lower levels of apoptosis when maintained in SF-medium. On the other hand, transient transfection of a dominant-negative Raf-1 construct (K375W-Raf-1) did not decrease apoptosis; slightly increasing DNA fragmentation levels were seen. Similar results were obtained when the cells were incubated in the presence of a MEK1 inhibitor. The results presented here suggest that overexpression of Crk-II induces apoptosis via a Ras-dependent, Raf-1/MEK1/ERK-independent pathway.

Apoptosis↗
PubMed1997

The insulin-like growth factor-I receptor signaling pathways are important for tumorigenesis and inhibition of apoptosis.

The biological actions of the insulin-like growth factors IGF-I and IGF-II are mediated by their activation of the IGF-IR, a transmembrane tyrosine kinase linked to the ras-raf-MAPK cascade. Functional IGF-IRs are required for the cell to progress through the cell cycle. Most importantly, cells lacking this receptor cannot be transformed by any of a number of dominant oncogenes, a finding that proves that the presence of the IGF-IR is important for the development of a malignant phenotype. Consistent with this role, the IGF-IR displays a potent antiapoptotic effect, both in vitro and in vivo. Because of its key role in the transformation process, the IGF-IR is actively studied as a potential therapeutic target in different types of neoplastic growth.

Animals↗
PubMed1996

Signaling via the insulin-like growth factor-I receptor: does it differ from insulin receptor signaling?

The insulin and insulin-like growth factor (IGF-I) receptors while similar in structure and function serve different physiological functions in vivo. In non-disease states the insulin receptor is primarily involved in metabolic functions whereas the IGF-I receptor mediates growth and differentiation. The separation of these functions is controlled by a number of factors including the tissue distribution of the respective receptors. Modulation of the binding of the ligands insulin or IGF-I and IGF-II to their respective receptors by the local environment of the cell also offers signaling specificity mediated via the receptors. Each ligand bind to its respective receptor with high affinity. This high affinity binding is dictated by the primary sequence of both the ligand and the receptor. Furthermore IGF-binding proteins are specific for IGF-I and IGF-II thereby modulating the binding of the IGFs to the IGF-I receptor. In contrast insulin circulates unbound to any proteins and interacts in the free state with the insulin receptor. It has been postulated that downstream substrates of the activated receptors differ in their specificity for the receptors, thus lending further specificity to the actions mediated by the receptors. While a number of known endogenous substrates such as IRS-1, IRS-2 and She are utilized by both receptors, the structural differences in the beta subunits of the two receptors has lead investigators to suggest that certain substrates may be unique to each receptor. Candidate substrates which show this specificity of action have been and are being described. Full eludication of the specificities of the insulin and IGF-I signaling pathways is of interest of course for a better understanding of intercellular communication. In addition, because the closely related proteins insulin and IGF-I are used clinically, a clear understanding of the pathways activated by these agents is essential if more specific therapeutic modalities are to be developed for use in disease states.

Binding Sites↗
PubMed1995

Hypoglycemia in pregnancy secondary to a non-islet cell tumor of the pleura and ectopic insulin-like growth factor II hormone production.

BACKGROUND: In nondiabetic women, pregnancy alone rarely causes clinical hypoglycemia. Non-islet cell tumors have recently been shown to be associated with the production of insulin-like growth factor II (IGF-II) and a paraneoplastic syndrome resulting in hypoglycemia. A case report and review of pathophysiologic mechanisms involved is presented. CASE: A 38-year-old multigravida presented suffering from clinical and biochemical hypoglycemia, which was found to be secondary to a mesothelioma of the pleura and ectopic IGF-II production. Tumor resection was performed during the 13th gestational week. The mother became euglycemic immediately after the surgery and remained asymptomatic. Clinical indicators of pregnancy and an ultrasound scan after the surgery were consistent with a normal viable fetus. CONCLUSION: Symptomatic hypoglycemia and other medical conditions occurring during pregnancy require immediate diagnosis and treatment. In addition to the more common causes, documented cases of medical conditions due to paraneoplastic syndromes of ectopic hormone production during pregnancy have been described. This case establishes the non-islet cell tumor with IGF-II-induced hypoglycemia as another such syndrome to be considered when evaluating hypoglycemia in pregnancy.

Adult↗
PubMed1987

Insulin receptors and insulin action in dissociated brain cells.

The present study was conducted to characterize insulin receptors and insulin action in rat brain cells. Binding of [125I]insulin to cells obtained by mechanically dissociating rat brains was 86% specific, time-dependent and reached equilibrium within 90 min. The t1/2 of association was 14 min and t1/2 of dissociation was 8 min. Scatchard analysis demonstrated the typical curvilinear plot providing high affinity (0.03 nM) and low affinity (6.6 nM) binding sites. The total number of binding sites were 0.15 pmol/mg protein. Crosslinking of [125I]insulin to its receptors on dissociated brain cells followed by SDS-PAGE and autoradiography showed that the alpha-subunit of the receptor had a molecular weight of 122,000. This was in contrast with a molecular weight of 134,000 for the liver alpha-subunit. Incubation of dissociated brain cells with insulin resulted in a concentration-dependent inhibition of total [3H]norepinephrine (NE) uptake. This inhibitory effect of insulin on [3H]NE uptake was sodium ion-dependent suggesting that 80-90% of the sodium ion-dependent uptake was insulin-sensitive. Incubation of lectin-purified insulin receptors with insulin resulted in a time- and concentration-dependent stimulation of phosphorylation of the tyrosine residue of an exogenous substrate poly (Glu, Tyr) (4:1). In addition, insulin also stimulated the autophosphorylation of the beta-subunit of the insulin receptors. These observations corroborate our contention that insulin exerts neuromodulatory effects mediated by the specific insulin receptors in the brain.

Animals↗
PubMed1983

Are messenger molecules in microbes the ancestors of the vertebrate hormones and tissue factors?

Peptides very similar to hormones and other messenger molecules of vertebrates have been detected in extracts of unicellular eukaryotes (and prokaryotes). We present arguments to suggest the possibility that these molecules 1) originated evolutionarily in unicellular microbes, 2) serve as intercellular messenger molecules in these organisms, and 3) represent the phylogenetic ancestors of the hormones and neurotransmitters as well as paracrine and other tissue factors of the vertebrates. We suggest that the biochemical elements of intercellular communication arose very early in evolution and are highly conserved; evolution largely changed the anatomy, i.e., the nature of the secretory cell, the target cell, and the fluid compartment that carries the messenger molecule from one to the other. Such an approach suggests a more rational relationship between different modes of intercellular chemical signaling in vertebrates.

Animals↗
PubMed1983

Two distinct insulins in the guinea pig: the broad relevance of these findings to evolution of peptide hormones.

In this paper we use the published data of others as well as our own recent data to question the widespread assumption that the gene for guinea pig insulin mutated rapidly after the divergence of guinea pigs from the main line of rodent evolution. We suggest that instead guinea pigs may have two pairs of alleles, one for typical guinea pig insulin, which is expressed in its pancreatic beta cells, and the other for a more typical mammalian insulin (designated rat/pork-type insulin), which is expressed in extrapancreatic cells. Further, we suggest the possibility that both pairs of genes may be evolutionarily very ancient and highly conserved. We also review evidence that the concept of nonallelic evolution may also apply to other hormones, including vasopressin, calcitonin, and growth hormone.

Alleles↗