title: Rat chondrocyte-associated antigen identified as sialylated transmembrane protein Tmp21 belonging to the p24 protein family.
abstract: Rabbit serum produced after transplantation of isolated rat chondrocytes [sensitized rabbit serum (SRS)] demonstrated M r ~ 74- and ~23-kDa (western blot analysis) antigens in rat chondrocyte extracts. Only the latter remained after reduction in 2-mercaptoethanol. Protein sequence analysis of 23-kDa chondrocyte-associated antigen (CAA) revealed that it corresponds to transmembrane Tmp21 protein belonging to the p24 protein family. These proteins mainly participate in the traffic between the endoplasmic reticulum and Golgi complex and in some cells appear also in the membrane of secretory granules and plasmalemma. Tmp21 extracted from chondrocytes was sialylated and ceased to bind SRS after deglycosylation. A previous study from our laboratory indicated that expression of CAA, now identified as sialylated Tmp21, decreased in cultured chondrocytes concomitantly with the decline of collagen type II and aggrecan and the rise of collagen type I and versican expression. Since the sialylated form of Tmp21 (also known as emp24) was not described in other tissues and seems to be specific for chondrocytes, we assume that CAA may be considered a chondrocyte differentiation antigen.
authors.affiliation: Department of Histology and Embryology, Medical University of Warsaw, Chalubińskiego 5, 02004, Warsaw, Poland, aosiecka@ib.amwaw.edu.pl.
authors.forename: Anna
authors.initials: A
authors.lastname: Osiecka-Iwan
authors.forename: Justyna
authors.initials: J
authors.lastname: Niderla-Bielinska
authors.forename: Anna
authors.initials: A
authors.lastname: Hyc
authors.forename: Stanislaw
authors.initials: S
authors.lastname: Moskalewski
mesh_terms: D053674:Aggrecans / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002358:Cartilage, Articular / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism*; D024043:Collagen Type II / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D011917:Rats, Inbred Lew
chemical_list: D053674:Aggrecans; D024043:Collagen Type II; D008565:Membrane Proteins; C100672:Tmed10 protein, rat