To characterize tissue-specific differences in insulin signaling, we compared the mechanisms of mitogen-activated protein (MAP) kinase activation by insulin in the mitogenically active 3T3-L1 fibroblasts with the metabolically active 3T3-L1 adipocytes. In both cell lines, insulin significantly increased p21 ras ⅐GTP loading (1.5-2-fold) and MAP kinase activity (5-8-fold). Inhibition of Ras farnesylation with lovastatin blocked activation of p21 ras and Raf-1 kinase in both 3T3-L1 fibroblasts and 3T3-L1 adipocytes. In 3T3-L1 fibroblasts, this was accompanied by an inhibition of the stimulatory effect of insulin on MAP kinase. In contrast, in 3T3-L1 adipocytes, despite an inhibition of activation of p21 ras and Raf-1 by lovastatin, insulin continued to stimulate MAP kinase activity. Fractionation of the cell lysates on the FPLC Mono-Q column revealed that lovastatin inhibited insulin stimulation of ERK2 (and, to a lesser extent, ERK1) in 3T3-L1 fibroblasts and had no effect on the insulin-stimulated ERK2 in 3T3-L1 adipocytes. These results demonstrate an important distinction between the mechanism of insulin signaling in the metabolically and mitogenically active cells. Insulin activates MAP kinase by the Ras-dependent pathway in the 3T3-L1 fibroblasts and by the Ras-independent pathway in the 3T3-L1 adipocytes.Insulin's interaction with its cell surface receptor triggers both metabolic and mitogenic cellular responses. Insulin binding activates the tyrosine kinase of the ␤-subunit of the insulin receptor, which immediately phosphorylates insulin receptor substrate-1 and Shc. Phosphorylated sites of insulin receptor substrate-1 and Shc bind Src homology-2 domain-containing intermediates such as phosphatidylinositol 3-kinase (PI 3-kinase) 1 and Grb-2, which, in turn, propagate insulin signaling downstream. PI 3-kinase appears to be involved in regulation of glucose transport and protein synthesis, while Grb-2 association with Sos appears to be an important step in activating the Ras-Raf-MEK-MAP kinase pathway (reviewed in Ref. 1).Although many intermediates of the insulin signaling have been identified, numerous questions remain unanswered. In particular, most of the signaling molecules activated by insulin are also significantly stimulated by other growth factors, such as platelet-derived growth factor and EGF (2). However, in contrast to these growth factors, only insulin elicits defined metabolic responses, suggesting that additional steps must be involved in the mechanism of insulin action.Recent studies from our laboratory have identified significant differences between the regulation of certain aspects of insulin signaling in metabolically responsive 3T3-L1 adipocytes and mitogenically responsive 3T3-L1 fibroblasts (3, 4). For example, in 3T3-L1 adipocytes, PI 3-kinase and PKC exert a constitutively inhibitory influence on GTPase-activating protein (GAP), allowing insulin signaling to proceed through Sos and p21ras . Removal of this inhibitory influence results in activation of GAP and inhibition of the p21 r...

In this study, we investigated the influence of the protein kinase C (PKC)-dependent system upon the ability of insulin to stimulate p21(ras).GTP loading in 3T3-L1 adipocytes. Activation of PKC by 12-0-tetradecanoylphorbol-13-acetate (TPA) did not affect the basal amount of p21(ras).GTP but significantly reduced insulin-induced increases in p21(ras).GTP. This reduction was due to inhibition of the insulin's ability to stimulate guanine nucleotide exchange activity of Sos in cells incubated with 100 nM TPA for either 30 min or 3 h. TPA had no effect on basal activity of Sos. Depletion of PKC by an 18-h incubation with TPA or inhibition by bisindolylmaleimide resulted in profound inhibition of the insulin-induced p21(ras).GTP loading. In contrast to PKC activation, removal of PKC did not influence Sos activity but resulted in a 2-fold stimulation of GTPase activating protein (GAP). This effect of PKC depletion is unique to 3T3-L1 adipocytes and was not observed in either 3T3-L1 fibroblasts or Rat-1 fibroblasts. Thus, it appears that in 3T3-L1 adipocytes, PKC has a constitutive inhibitory effect on GAP that permits insulin to activate Sos and p21(ras). Removal of this inhibitory influence activates GAP and reduces insulin-stimulated p21(ras).GTP loading.

Sirolimus is an immunosuppressive agent approved for prophylaxis of acute rejection in renal transplant patients aged 13 years or older. A retrospective review of pericardial effusion coincident with sirolimus therapy was conducted from key clinical trials and spontaneous reporting sources. A significantly higher rate of pericardial effusion occurred with sirolimus versus azathioprine treatment in a cardiac transplantation trial (28.6% versus 9.3%, respectively). Cases of pericardial effusion were also observed in the sirolimus treatment arms of three de novo renal transplant studies (rates 0.5 to 1.9%). Although most of the pericardial effusions occurred in cardiac transplantation, sirolimus is not approved for this use. As of January 31, 2007, the Wyeth safety database (which includes clinical trial data and spontaneous reports) contained reports of pericardial effusion in 56 sirolimus-treated patients, 31 of whom required pericardial drainage. These data suggest that pericardial effusion should be considered in the differential diagnosis of a clinical deterioration in posttransplant patients treated with sirolimus. The adverse reaction of pericardial effusion has been added to product labeling.

An enzyme immunoassay for the diagnosis of syphilis (ELISA-SY) was developed with solid-phase extracts of Treponema pallidum, specimen diluent containing Reiter treponeme absorbent, and three 30-min incubations. The ELISA-SY results were determined in comparison with a standardized positive control and reported as a percentage of strong positive control. In tests with 1,005 serum samples from a venereal disease clinic and other sources, 98.2% agreement was found with fluorescent treponemal antibody-absorption (FTA-ABS) results, and 98.3% agreement was found with T. pallidum passive hemagglutination (PHA) findings. Only 1 of 29 sera originally considered to be biologically false-positive was positive by ELISA-SY; the latter specimen was also positive by PHA and FTA-ABS tests performed in our laboratories. Serum samples from clinically diagnosed syphilitics (16 primary-stage isolates, 7 secondary-stage isolates, and 3 latent-stage isolates) were all positive by ELISA-SY, FTA-ABS, and PHA. Serum samples from 51 newborns suspected of having syphilis on the basis of positive cardiolipin flocculation tests showed 98% agreement of ELISA-SY results with FTA-ABS and PHA findings. Sera from all 61 patients with a variety of autoimmune and other diseases known to be associated with biologically false-positive reactions for syphilis were negative by this ELISA-SY. The specificity of the ELISA procedure for T. pallidum antibody was also confirmed immunologically by blocking experiments.

The fluorescent treponemal antibody-absorption double-staining step-by-step procedure and proposed reference reagents for the test are described. The test and reagents were evaluated in two separate laboratories on 265 fresh sera, and test results were compared with the reference fluorescent treponemal antibody-absorption test results performed in a third laboratory. The data indicate that the tests are comparable in the areas where the test is recommended for use. Problems with inadequate light filtration occurred, but these could be resolved. This test is recommended for use with microscopes equipped with incident illumination.