摘要:

AbstractMicrovilli were isolated from cultured human JEG‐3 choriocarcinoma cells using a gentle shearing method. The protein components of the isolated microvilli were examined by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and immunoblotting. The major Mr42,000 and Mr100,000 polypeptide bands reacted with anti‐actin and anti‐α‐actinin antisera, respectively. Extraction of the isolated JEG‐3 microvilli with Triton X‐100 left an insoluble cytoskeletal residue containing mainly actin, α‐acinin, and polypeptides of Mr200,000, 55,000 and 35,000. The Mr35,000 polypeptide remained insoluble only at high concentrations of free Ca2+. Immunoblotting analysis of the JEG‐3 microvilli indicated that they were devoid of tropomyosin, although the total JEG‐3 protein lysates gave a strong positive reaction with anti‐tropomyosin, antiserum. The different subcellular localization of cytovillin and tropomyosin was also shown by indirect immunofluorescence microscopy. Cytovillin, an Mr75,000 microvillus‐specific membrane protein of JEG‐3 cells, existed in an oligomeric form (dimer or trimer) as shown by gel filtration of Triton X‐100 solubilized microvillar proteins and by native polyacrylamide gel electrophoresis of purified cytovillin. Disulfide bridges were not involved in the aggregation, because the mobility of cytovillin was similar under reducing and nonreducing conditions in SDS‐PAGE. Cytovillin was shown to be closely related to ezrin, a minor component of chicken i

ISSN:0730-2312    

DOI:10.1002/jcb.240410102

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe inability of HT‐29 cells to undergo an enterocytic differentiation when grown in a glucose‐containing (Glc+) medium has been recently correlated to an overall impairment of N‐glycan processing. These results were obtained using confluent HT‐29 cells in which the differentiation characteristics are fully expressed under differentiation permissive conditions (glucose‐deprived medium, Glc−). Whether these changes of N‐glycan processing appear progressively during the cell growth or are already present from the beginning of the culture was investigated in this work by comparing the actual status of N‐glycan processing in both exponentially growing Glc+and Glc−HT‐29 cells. Under these conditions, HT‐29 cells do not express any characteristics of enterocytic differentiation, even when grown in differentiation permissive conditions. We show here that the conversion of high‐mannose to complex glycoproteins is, however, severely reduced in HT‐29 cells grown studied. In contrast, HT‐29 cells grown in differentiation permissive conditions (HT‐29 Glc−) display a normal pattern of N‐glycan processing in both the exponential and the stationary phase of growth. We also show that both growing and confluent HT‐29 Glc+cells accumulate Man9–8GlcNAc2species, thus suggesting that there is an important regulatory point at this level. We therefore conclude that the N‐glycan processing may be used as an early biochemical probe for the enterocytic differentiation of HT‐29 cells. Whether these early changes result from an early metabolic regulation or are the consequence o

ISSN:0730-2312    

DOI:10.1002/jcb.240410103

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe effects of red blood cell (RBC) age on membrane thermal properties have been investigated by using a 16‐nitroxide stearic acid spin probe. We detected in unfractionated and most dense cells (2% fraction of circulating cells) a thermal transition at 40°C that in young cells (1% fraction) was lowered at 33–35°C. Spectrin seems to be directly involved in the transition detected in both young and unfractionated cells, as showed by the disappearance of the breaks after low salt extraction of spectrin. A further indication for a role of spectrin in this transition comes from its characteristic thermal unfolding above 40°C.However, young cells did not show changes either in the thermal unfolding of spectrin or in the distribution of spectrin dimer, tetramer, and high oligometric forms. These data rule out that spectrin of young RBC is modified in its thermal properties and indicate that young cells may have a different spectrin‐membrane interaction.Treatment of unfractionated ghosts with an antibody specific for a fragment of the 10K domain of protein 4.1, which is fully competent for the spectrin‐actin binding, produced an evident lowering of the transition temperature. The same antibody did not affect the thermal transition of young ghosts. Our results suggest that spectrin‐membrane interactions may be regulated during

ISSN:0730-2312    

DOI:10.1002/jcb.240410104

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe role of trimming and processing of N‐linked oligosaccharides on the cell surface expression of the melanoma vitronectin receptor, a member of the integrin family of cell adhesion receptors, was examined by using specific glucosidase and mannosidase inhibitors. Inhibition of glucosidases I and II by castanospermine or N‐methylde‐oxynojirimycin delayed the vitronectin receptor α/β chain heterodimer assembly and α chain cleavage and resulted in a decrease in the level of expression cell surface receptor. Conversely, the vitronectin receptor synthesized in the presence of the mannosidase I and II inhibitors, 1‐deoxymannojirimycin and swainsonine, was transported normally to the cell surface with its α chain N‐linked oligosaccharides in an endoglycosidase H–sensitive from. In the presence of swainsonine, time course studies of the cell surface replacement of control, endoglycosidase H–resitant receptor with an endoglycosidase H–sensitive form demonstrated a vitronectin receptor half‐life of approximately 15–16 h. These studies provide evidence that the rates of assembly, proteolytic cleavage, and cell surface expression of the melanoma vitronectin receptor are dependent on the initial trimming of glucosyl residues from the α chain N

ISSN:0730-2312    

DOI:10.1002/jcb.240410105

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

年代:1989

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240410106

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

年代:1989

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240410107

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

年代:1989

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240410101

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

年代:1989

数据来源: WILEY