Peroxisome proliferator-activated receptor (PPAR)-gamma plays an important role in adipogenesis. However, the functions of PPAR-gamma in differentiated adipocytes have remained unclear. The role of ...PPAR-gamma in mature 3T3-L1 adipocytes was therefore investigated by overexpression of a dominant negative mutant of this protein (PPAR-gamma-DeltaC) that lacks the 16 COOH-terminal amino acids and that has been shown to prevent the thiazolidinedione-induced differentiation of 3T3-L1 cells into adipocytes. Overexpression of PPAR-gamma-DeltaC in mature 3T3-L1 adipocytes by adenovirus gene transfer resulted in a decrease in both cell size and intracellular triglyceride content, an increase in the extent of lipolysis, and a reduction in the rate of free fatty acid uptake. Furthermore, overexpression of this mutant reduced the abundance of mRNAs for several key enzymes that contribute to triglyceride and free fatty acid metabolism as well as the amounts of GLUT4, insulin receptor, insulin receptor substrate (IRS), and C/EBPalpha mRNAs. It also reduced both the concentration of IRS2 and the insulin-stimulated glucose uptake. These results suggest that PPAR-gamma plays an important role in mature 3T3-L1 adipocytes at least in part by maintaining the expression of genes that confer the characteristics of mature adipocytes.
SNARE proteins have been implicated in the insulin-induced translocation of vesicles containing the GLUT4 glucose transporter to the plasma membrane of adipocytes. The role of the target SNARE ...SNAP-25 or its homologs in this process was investigated by screening a mouse adipocyte cDNA library with rat SNAP-25 and human SNAP-23 cDNA probes. Both positive clones isolated encoded a protein with 87% sequence identity to human SNAP-23, and which was therefore designated mouse SNAP-23. Immunoblot and immunofluorescence analyses revealed that SNAP-23 is located predominantly in the plasma membrane of 3T3-L1 adipocytes incubated in the absence or presence of insulin. Of syntaxins 1 to 5, SNAP-23 bound with the highest affinity to syntaxins 1 and 4 in the yeast two-hybrid system. Expression of SNAP-23, syntaxin 4, and the syntaxin-binding protein Munc18c in COS cells revealed that Munc18c reduced the amount of SNAP-23 bound to syntaxin 4 in a concentration-dependent manner. These results suggest that the binding of SNAP-23 to syntaxin 4 is inhibited by Munc18c in adipocytes.
Peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the nuclear hormone receptor superfamily of transcription factors and appears to be a key regulator of adipogenesis. Members of the ...thiazolidinedione class of insulin-sensitizing agents act as high-affinity ligands for PPARγ, indicating that PPARγ is also important in systemic insulin action. To determine whether Pro12 → Ala (P12A) mutation in PPARγ gene contributes to the development of obesity or insulin sensitivity, we examined the effects of the P12A mutation on the function of PPARγ by expression of the mutant protein in COS or 3T3-L1 cells. The abilities of the P12A mutant of PPARγ to mediate both transcriptional activation of a luciferase reporter gene construct containing the peroxisome proliferator response element and adipogenesis induced by a thiazolidinedione drug were reduced compared with those of the wild-type protein. These results suggest that the P12A substitution in PPARγ gene may be associated with abnormalities of adipose tissue formation and insulin sensitivity.
Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor that is thought to be an important regulator of adipocyte differentiation. This ligand-dependent transcription factor is ...also activated by thiazolidinediones, a new class of synthetic antidiabetic drugs, resulting in a marked adipogenic response in cultured cells and enhanced insulin sensitivity in vivo. The importance of the COOH-terminal region of PPARγ2 in thiazolidinedione-induced adipogenesis has now been investigated by expression of a mutant protein (PPARγ2-ΔC) that lacks the COOH-terminal 16 amino acids of full-length PPARγ2. The mutant protein failed to bind a thiazolidinedione ligand, but its ability to bind the peroxisome proliferator response element was similar to that of the wild-type protein. Expression of PPARγ2-ΔC inhibited the thiazolidinedione-induced increase in trans-activation activity of endogenous PPARγ in CV-1 cells. Furthermore, the mutant protein prevented thiazolidinedione-induced adipogenesis in 3T3-L1 cells, whereas expression of recombinant wild-type PPARγ2 promoted adipogenesis. These data show not only that the COOH-terminal region of PPARγ2 is indispensable for thiazolidinedione-induced adipogenesis mediated by this protein in 3T3-L1 cells, but also that the PPARγ2-ΔC mutant acts in a dominant negative manner by interfering with the access of endogenous PPARγ to the peroxisome proliferator response element of target genes.
Treatment with a combination chemotherapeutic regimen consisting of cyclophosphamide, vincristine, and dacarbazine for malignant paraganglioma with hepatic metastasis is reported. A 51-year-old male ...presented with tumors in the retroperitoneal space and liver. The patient was diagnosed as having paraganglioma based on elevated levels of serum neuron-specific enolase, urinary catecholamine and vanillylmandelic acid, and on histological findings of the liver specimen. The patient was treated with this combination chemotherapy in repeated 21-day cycles. Temporary improvement in laboratory findings and a 20% reduction in the size of the hepatic masses were observed without severe adverse effects. (Internal Medicine 36: 35-39, 1997)
Ascorbic acid, reported in 1988 to be effective for idiopathic thrombocytopenic purpura (ITP), is an attractive drug because of its lack of toxicity. Further studies are necessary in order to improve ...its effectiveness without increasing secondary effects. We present a chronic ITP patient treated with a combination of ascorbic acid and methylprednisolone pulse (MP) therapy who was previously treated with MP therapy alone. The effect of this combination therapy seems to be better than MP therapy alone. This therapy is worth further examination as another therapeutic choice due to its fewer secondary effects than the usual regimen of corticosteroids, splenectomy, and other immunosuppressive drugs. (Internal Medicine 33: 165-166, 1994)
A patient with pigmentary retinopathy, nephrotic syndrome, Ménétrier's disease, and diabetes mellitus is presented. Other complications were congestive heart failure, hypothyroidism, hypertension, ...and hypertriglyceridemia. Hypogenitalism was also suspected. Pigmentary retinopathy is known to associate with many systemic diseases, which are classified into several syndromes. This case superficially resembles Alström's disease due to the common characteristics of pigmentary retinopathy, diabetes mellitus, renal disease, and hypogenitalism. But clinically and histologically, there are distinct differences. To our knowledge, this association has never been reported. (Internal Medicine 33: 644-648, 1994)
The mouse obese (ob) gene has recently been isolated through the positional cloning technique and has been proved to result in the obese and NIDDM phenotype in mice when mutated (Nature 372:425-432, ...1994). More recently, it has been demonstrated, by experiments with recombinant ob protein, that ob gene product can cause mice, including ob/ob mice, diet-induced obesity mice, and normal mice, to lower their food intake and body weight (Science 269:540-549, 1995). To investigate the genetic and/or environmental influences underlying the development of NIDDM associated with obesity, we isolated and partially sequenced the human obese (OB) gene. The human OB gene isolated in this study encoded 167 amino acids and its open reading frame was revealed to be divided into two parts with an intermediate intron of approximately 2.4 kb. Using the single-strand conformation polymorphism (SSCP) technique, we screened Japanese and Asian Indian subjects for mutations in the protein coding regions of the OB gene. A total of 75 NIDDM patients with obesity (54 Japanese and 21 Asian Indians), 40 NIDDM patients without obesity (34 Japanese and 6 Asian Indians), and 34 Japanese patients with simple obesity showed no abnormal SSCP patterns in either component of the coding sequences. These results suggested that mutations in the coding regions of the OB gene are not likely to be commonly identifiable and that there would likely be a kind of obesity-associated NIDDM not caused by mutations of the OB gene.
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