Synergistic induction of insulin resistance by endothelin-1 and cAMP in 3T3-L1 adipocytes.

Both endothelin-1 (ET-1) and cAMP are implicated for inducing insulin resistance. Since we have shown previously that there is a crosstalk between ET-1 and cAMP signaling pathways in regulating glucose uptake in 3T3-L1 adipocytes, we extended our investigation in this study on whether they may have a synergistic effect on inducing insulin resistance. Our results showed that it was indeed the case.

The PTTG1-binding factor (PBF/PTTG1IP) regulates p53 activity in thyroid cells.

The PTTG1-binding factor (PBF/PTTG1IP) has an emerging repertoire of roles, especially in thyroid biology, and functions as a protooncogene. High PBF expression is independently associated with poor prognosis and lower disease-specific survival in human thyroid cancer. However, the precise role of PBF in thyroid tumorigenesis is unclear.

Depletion of SUMO ligase hMMS21 impairs G1 to S transition in MCF-7 breast cancer cells.

Background: hMMS21 is a human SUMO ligase required for DNA damage repair and mitotic progression in HeLa cervical cancer cells. Owing to the diversity of cancer, we further investigated the effect of hMMS21-depletion on MCF-7 breast cancer cells.

Methods: hMMS21-depletion was achieved by RNA interference.

A novel cross-talk between endothelin-1 and cyclic AMP signaling pathways in the regulation of GLUT1 transcription in 3T3-L1 adipocytes.

We showed previously that chronic exposure to both endothelin-1 (ET-1) and cAMP resulted in a synergistic increase in Glut1 transcription in 3T3-L1 adipocytes via a protein kinase C (PKC)-dependent mechanism. In the present study, we further examined the molecular mechanism involved. Employing transient transfections with Glut1 promoter/enhancer -luciferase reporter and several dominant negative or constitutively active PKC mutants, we identified PKCε as the responsible PKC.

Titanium versus autograft ossiculoplasty.

Conclusion: In this comparative series, hearing results were superior with titanium compared with autograft ossiculoplasty in the absence of a stapes superstructure. However, in the presence of a stapes superstructure, titanium ossiculoplasties gave superior results to autografts only when comparing an air-bone gap of < 10 dB.

Objective: To compare the hearing outcomes of autograft versus titanium ossiculoplasty at 1 year.

A novel mechanism of sodium iodide symporter repression in differentiated thyroid cancer.

Differentiated thyroid cancers and their metastases frequently exhibit reduced iodide uptake, impacting on the efficacy of radioiodine ablation therapy. PTTG binding factor (PBF) is a proto-oncogene implicated in the pathogenesis of thyroid cancer. We recently reported that PBF inhibits iodide uptake, and have now elucidated a mechanism by which PBF directly modulates sodium iodide symporter (NIS) activity in vitro.

Endothelin-1 stimulates interleukin-6 secretion from 3T3-L1 adipocytes.

Background: Since both endothelin-1 (ET-1) and interleukin-6 (IL-6) may induce insulin resistance and adipose tissue is a major contributor of circulating IL-6, we examined the effects of ET-1 on IL-6 secretion from 3T3-L1 adipocytes.

Methods: IL-6 release was measured by ELISA. RT-PCR and real-time PCR analyses were used to determine cellular IL-6 mRNA levels.

Endothelin-1 induces glut1 transcription through enhanced interaction between Sp1 and NF-kappaB transcription factors.

We have shown previously that endothelin-1 (ET-1) induction of Glut1 transcription is mediated by ET-1 responsive elements on enhancer 2, via both protein kinase Cepsilon (PKCepsilon)- and p42/p44 mitogen-activated protein kinase (MAPK)-dependent pathways. In the present study, we further explored the molecular mechanism involved. By using mutation constructs of luciferase reporter driven by Glut1 promoter/enhancers, chromatin immunoprecipitation and co-immunoprecipitation experiments, we were able to demonstrate that cooperative interaction between NF-kappaB and Sp1 were required to enhance Glut1 transcription in response to ET-1.

Endothelin-1 induction of Glut1 transcription in 3T3-L1 adipocytes involves distinct PKCepsilon- and p42/p44 MAPK-dependent pathways.

We have shown previously that chronic exposure to endothelin-1 (ET-1) may stimulate GLUT1-mediated glucose transport in 3T3-L1 adipocytes via both protein kinase C (PKC)- and mitogen-activated protein kinase (p42/p44 MAPK)-dependent pathways. In the present study, by using a luciferase reporter driven by Glut1 promoter and enhancers (pLuc-GT1/E1/E2) and various constitutively active and dominant negative mutants of PKC isoforms, we identified PKCepsilon as the PKC isoform involved. In addition, we provide evidence that there is no direct interaction between ET-1 activated PKCepsilon and MAPK, at least at the kinase activity level.

Pretreatment with muscarinic receptor agonist activates a calcium-inhibitable adenylate cyclase in GH3 pituitary cells.

We have demonstrated previously that pretreatment of GH3 pituitary cells with muscarinic agonists may induce a higher cAMP formation in response to vasoactive intestinal peptide (VIP) or forskolin. In the present study, we further examined the adenylate cyclase (AC) that may be involved. We found that carbachol-pretreatment enhanced both VIP- and forskolin-activated AC activities.

Synergistic effect of prostaglandin F2alpha and cyclic AMP on glucose transport in 3T3-L1 adipocytes.

The combined effect of prostaglandin F2alpha (PGF2alpha) and cAMP on glucose transport in 3T3-L1 adipocytes was examined. In cells pretreated with PGF2alpha and 8-bromo cAMP for 8 h, a synergy between these two agents on glucose uptake was found. Insulin-stimulated glucose transport, on the other hand, was only slightly affected.

Synergistic effect of endothelin-1 and cyclic AMP on glucose transport in 3T3-L1 adipocytes.

We have demonstrated previously that chronic exposure to endothlin-1 enhances glucose transport in 3T3-L1 adipocytes via augmented GLUT1 mRNA and protein accumulation. In the present study, we further examined the combined effect of endothelin-1 (ET-1) and cAMP on glucose transport. In cells pretreated with ET-1 and 8-bromo cAMP for 8 h, a synergy between these two agents on glucose uptake was found.

Thapsigargin and EGTA inhibit endothelin-1-induced glucose transport.

We have previously demonstrated that ET-1 may enhance glucose transport in 3T3-L1 adipocytes, secondarily to its stimulatory effect on GLUT1 gene expression by a mitogen-activated protein kinase (MAPK)-dependent pathway. In the present study, we further tested the involvement of Ca(2+) in glucose uptake in response to ET-1. Among a variety of Ca(2+)-related agents tested, EGTA and thapsigargin were found to suppress both the glucose uptake and intracellular Ca(2+) mobilization induced by ET-1, as determined by Fura-2 analysis.

Prostaglandin F2alpha increases glucose transport in 3T3-L1 adipocytes through enhanced GLUT1 expression by a protein kinase C-dependent pathway.

The effect of prostaglandin F2alpha (PGF2alpha) on glucose transport in differentiated 3T3-L1 adipocytes was examined. Whereas PGF2alpha had little influence on insulin-stimulated 2-deoxyglucose uptake, it increased basal glucose uptake in a time- and dose-dependent manner, reaching maximum at approximately 8 h. The long-term effect of PGF2alpha on glucose transport was inhibited by both cycloheximide and actinomycin D.

Differential effects of endothelin-1 on calcium mobility in cultured porcine pigment epithelial cells of iris and retina.

Background And Purpose: Photoreceptor function depends on an intact retina pigment epithelial (RPE) cell layer. Transplantation of iris pigment epithelial (IPE) cells to the subretinal space offers a potential alternative to RPE transplantation in patients with severe retinal diseases such as macular degeneration. Whether the functions of IPE and RPE are similar or different is not well established.

Effects of commercial antiglaucoma drugs to glutamate-induced [Ca2+)]i increase in cultured neuroblastoma cells.

Over releasing of glutamate and cellular calcium influx always results in neuronal death. In the present study, we investigated various commercial antiglaucoma drugs including timolol (0.58 microM to 58 microM), betaxolol (1.

Change of cytosolic Ca(2+) mobility in cultured bovine corneal endothelial cells by endothelin-1.

The effect of endothelin-1 (ET-1) on the intracellular free Ca(2+) ([Ca(2+)](i)) in cultured bovine corneal endothelial cells was studied after loading with fura-2-AM. In Ca(2+)-containing buffer and Ca(2+)-free buffer, ET-1 induced a significant rise in [Ca(2+)](i) at concentrations from 10(-9) to 10(-7) M. In Ca(2+)-free buffer, pretreatment of the cells with ET-1 inhibited thapsigargin-induced [Ca(2+)](i) increase and carbonylcyanide m-chlorophenylhydrazone (CCCP)-induced Ca(2+) release by 99% and 62%, respectively.

Mechanism of inhibition of insulin-stimulated glucose transport by 4-bromocrotonic acid in 3T3-L1 adipocytes.

We have demonstrated previously that 4-bromocrotonic acid (Br-C4) inhibited insulin-stimulated glucose transport by interfering with GLUT4 translocation. In the present study, we further examined the underlying mechanism involved. Since insulin-induced insulin receptor substrate-1-associated phosphatidylinositol (PI) 3-kinase activity was not altered by Br-C4, we determined and found insulin activation of protein kinase B (PKB) and protein kinase Clambda (PKClambda) were both inhibited.

Possible mechanism of endothelin-induced Ca2+ mobility in A7r5 cultured vascular smooth muscle cells.

We studied the mechanism by which endothelin-1 (ET-1) affects the mobility of intracellular free Ca2+ ([Ca2+]i) in cultured A7r5 aortic smooth muscle cells. ET-1 at 10(-9) to 10(-7) M increased [Ca2+]i in Ca2+-containing buffer and Ca2+-free buffer. Pretreatment with ET-1 inhibited thapsigargin- and carbonylcyanide m-chlorophenylhydrazone (CCCP)-induced [Ca2+]i increases in Ca2+-free buffer.

Effects of crude drugs on lipolysis in differentiated 3T3-L1 adipocytes.

In the present study, aqueous fractions extracted from Radix Ginseng, Radix Rehmanniae, Radix Puerariae, Radix Asparagi, Cortex Phellodendri and Radix Scutellariae were investigated for their effects on lipolysis measured the glycerol release in cultured 3T3-L1 differentiated adipocytes cells. Following treatment of cells with various concentrations of water-soluble extracts ranging from 0.1, 1 to 10 mg/ml for 60 mim, the basal glycerol release from 3T3-L1 cells was changed from 71 nmole/mg protein of control to 48, 46 and 31 nmole/mg protein in Radix Ginseng-treated cells.

Nigericin inhibits insulin-stimulated glucose transport in 3T3-L1 adipocytes.

We used nigericin, a K+/H+ exchanger, to test whether glucose transport in 3T3-L1 adipocytes was modulated by changes in intracellular pH. Our results showed that nigericin increased basal but decreased insulin-stimulated glucose uptake in a time- and dose-dependent manner. Whereas the basal translocation of GLUT1 was enhanced, insulin-stimulated GLUT4 translocation was inhibited by nigericin.