摘要:

AbstractTransforming growth factor‐α (TGF‐α) stimulates (in a dose‐dependent manner) the incorporation of [32P]Pi into phosphatidylinositol(PI), phosphatidylinositol 4‐phosphate (PIP), phosphatidylinositol 4,5‐bisphosphate (PIP2), and phosphatidic acid (PA) in the human epidermoid carcinoma cell line (A431). The effect of TGF‐α on the incorporation was found to be similar to that of EGF. On the other hand, a striking difference in the activation of diacylglycerol (DG) kinase activity was seen between TGF‐α and EGF. At least 100 times more TGF‐α was required to achieve maximal stimulation of DG kinase activity relative to EGF. These results suggest that the activation of DG kinase by TGF‐α may involve a mechanism independent from or subsequent to activat

ISSN:0730-2312    

DOI:10.1002/jcb.240370402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractWe have studied the biosynthesis of the insulin receptor in a human hepatoma cell line, HepG2. As previously reported, these cells synthesize a disulphide–bonded α2β2tetrameric insulin receptor. Labelling of HepG2 cells with [3H]palmitate or [3H]myristate followed by immunoprecipitation with a polyclonal antireceptor antibody revealed the incorporation of palmitate, but not myristate, into the β‐subunit and αβ‐precursor of the receptor in a hydroxylamine‐sensitive linkage. The extracellular α‐subunit was not labelled, demonstrating the specificity of incorporation. Acylation of the insulin receptor was an early event as judged by fatty acid incorporation into the αβ‐precursor and prevention by protein synthesis inhibitors. Pulse‐chase studies demonstrated the expected processing of the αβ‐precursor to mature α‐ and β‐subunits, but no evidence for preferential turnover of the fatty acid moiety was found. The site of acylation appears to be in the transmembrane or cytoplasmic domain since proteolytic treatment of intact cells produced a truncated β‐subunit still containing label. Binding studies showed that HepG2 cells contain approximately half as many insulin‐like growth factor‐1 receptors as insulin receptors, raising the possibility that this receptor may also be acylated. Indeed, immunoprecipitation with the antiinsulin receptor serum of MDCK cells expressing IGF‐1 receptors, but not insulin receptors, revealed bands corresponding to the αβ‐precursor, α‐ and β‐subunits, of which the αβ‐precursor and β‐subu

ISSN:0730-2312    

DOI:10.1002/jcb.240370403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractAdenylate cyclase of aggregation phaseDictoystelium discoideumis activated by extracellular adenosine 3′, 5′‐cyclic monophosphate (cAMP), and the cAMP syn‐thesized is secreted. The distribution of the enzyme was determined in sucrose gradients loaded with whole cell lysates. Cell lysates prepared after 4.5 hr of starvation revealed membranes containing adenylate cyclase at 44% and 33% sucrose. The activity of the latter peak was detected in the presence of the detergent (CHAPS), 3‐(3‐cholamidopropyl) dimethylammonio‐3‐propanesulfonate, which inhibited the activity of the former to some extent. Adenylate cyclase activity of the 2 peaks differed with respect to solubility in CHAPS and their kinetics. The 44% sucrose region of the gradient contained the bulk of the plasma membranes, as judged by a cell surface glycoprotein marker (contact site A). The 33% peak is composed of small vesicular structures, as determined by electron microscopy. The distribution of adenylate cyclase activity detected in sucrose gradients shifted from the 33% to the 44% sucrose peak during development. In addition, the 44% peak became increasingly resistant to the inhibitory effect of CHAPS, Both changes were accelerated by extracellular cAMP, but only the latter was abolished when the production of endogeneous cAMP was inhibited by caffeine. Pulsing cells with cAMP overcame the inhibitory eff

ISSN:0730-2312    

DOI:10.1002/jcb.240370404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractIt is well established that somatotropin (GH) antagonizes insulin action in vivo and that supraphysiologic concentrations of GH frequently result in insulin resistance and glucose intolerance. However, the demonstration of an anti‐insulin activity by GH in vitro has been difficult. This study, therefore, set out to determine whether cultures of 3T3‐L1 adipocytes could be used to examine the anti‐insulin activity of GH. The ability of insulin to stimulate glucose utilization by 3T3‐L1 adipocytes increases approximately five‐fold during the first 4 days following treatment of the cells with a differentiation medium. It was found that glucose utilization in 3T3‐L1 adipocytes is regulated in a reciprocal fashion by insulin and GH. Bovine or human GH directly inhibit up to 50% of insulin‐stimulated [14C]‐glucose incorporation into lipids in a concentration‐dependent manner. The 3T3‐L1 sensitivity to GH appears to be at the maximum (50% inhibition of an insulin response) immediately following removal of the cells from the differentiation medium and remains essentially constant during the subsequent 4 days. The GH inhibition of insulin action does not appear to be due GH enhancement of cellular degradation of insulin, competitive binding of GH to the insulin receptor, or GH‐induced decrease in cell number. The 3T3‐L1 adipocyte system appears to be a sensitive and reliable in vitro model with which to study the molecular mechanisms involved in both GH antagonism of insulin action and development of hormone responsiveness during cellular differen

ISSN:0730-2312    

DOI:10.1002/jcb.240370405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe Very Late Activation Antigen (VLA) proteins are a family of five related heterodimers, which also are part of the integrin superfamily of cell adhesion molecules. Except for the identification of VLA‐5 as a fibronectin receptor structure, the functions of the VLA proteins have remained unclarified. In this paper, immuno‐precipitation experiments with both anti‐α and anti‐β subunit antibodies showed that the previously identified cell adhesion receptor for collagen, extracellular matrix receptor II (ECMRII), is equivalent to VLA‐2. At the same time a previously described multispecific cell adhesion receptor for collagen, fibroncclin, and laminin (ECMRI) has been shown to be identical to VLA‐3. Although the mAb 12F1 and P1H5 both recognized VLA‐2 (ECMRII), they appeared to define distinct epitopes on the α2subunit. On the other hand, the mAb PIB5 and J143 recognized the α3subunit of VLA‐3 (ECMRI) at or near the same site. Consistent with the collagen receptor functions of VLA‐2 (ECMRII) and VLA‐3 (ECMRI), anti‐VLA β antiserum blocked c

ISSN:0730-2312    

DOI:10.1002/jcb.240370406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe isolated brush border membrane of the tapeworm,Hymenolepis diminuta, hy‐drolyzes p‐nitrophenyl phosphate over a broad pH range. Acid phosphatasc activity (pH optimum at 4.0) is inhibited specifically by sodium dodecyl sulfate (SDS) and NaF, while the alkaline phosphatase activity (pH optimum at 8.8) is inhibited specifically by levamisole, 2‐mercaptoethanol, and ethylenediaminetetra‐acetate (EDTA). These two phosphatase activities are further differentiated in that (1) there is a rapid decrease in alkaline phosphatase activity when the membrane preparation is incubated at pH 4.0, while there is little loss of acid phosphatase activity, and (2) the alkaline phosphatase activity is solubilized with no loss of activity when the membrane is treated with Triton X‐100, while such treatment causes a significant loss of acid phosphalase activity. Both activities are nonspecific and hydrolyze a variety of phos‐phorylated compounds, but the relative activities of the two phosphatases against these substrates vary si

ISSN:0730-2312    

DOI:10.1002/jcb.240370407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240370401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY