Calcium-dependant binding proteins associated with human placental syncytiotrophoblast microvillous cytoskeleton.
Isolated human placental syncytiotrophoblast microvillous plasma membrane vesicles were extracted with Triton X-100 to yield a detergent-insoluble residue. The residue contained approx. 50% of the total membrane protein and was qualitatively different from untreated trophoblast on SDS-polyacrylamide gel electrophoresis, Western blots and dot-immunobinding assay. Three major proteins, with molecular weights of 68, 36 and 34 kDa, dissociated from this non-ionic detergent-insoluble submembranous cytoskeletal fraction in the presence of calcium chelators. They were immunologically related to human lymphocyte cytoskeletal calcium-binding proteins, and the 36 kDa component reacted with antisera to the phospholipase A2 inhibitor, lipocortin II. Anti-lipocortin I sera did not recognise the 34 kDa protein, but did react with a series of trophoblast cytoskeletal proteins in the 34-37 kDa region. Incubation of epidermal growth factor with isolated trophoblast membrane vesicles stimulated the phosphorylation of a 36 kDa protein on tyrosine residues. Immunoprecipitation studies further showed there was no phosphorylation of the 34 kDa protein, but the 68 kDa protein was a major phosphorylated component of isolated syncytiotrophoblast membranes. p68 was principally phosphorylated on serine with slight tyrosine phosphorylation which showed an apparent increase after epidermal growth factor treatment. These results indicate a family of calcium-dependant binding proteins, some of which are phosphorylated, associated with the submembranous cytoskeleton of syncytiotrophoblast microvilli.
Webb
P D
PD
Department of Immunology, University of Liverpool, U.K.
Mahadevan
L C
LC
D002135:Calcium-Binding Proteins / Q000032:analysis*; D003599:Cytoskeleton / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D007163:Immunosorbent Techniques; D008871:Microvilli / Q000032:analysis; D008970:Molecular Weight; D017830:Octoxynol; D010766:Phosphorylation; D010920:Placenta / Q000032:analysis*; D011092:Polyethylene Glycols; D012995:Solubility; D014327:Trophoblasts / Q000032:analysis*
D002135:Calcium-Binding Proteins; D011092:Polyethylene Glycols; D004815:Epidermal Growth Factor; D017830:Octoxynol