Sialomucin complex (rat Muc4) transmembrane subunit binds the differentiation marker peanut lectin in the normal rat mammary gland.
Sialomucin complex (SMC, rat Muc4) is a heterodimeric glycoprotein composed of two subunits, the mucin component ASGP-1 and the transmembrane subunit ASGP-2. SMC/Muc4 is highly expressed on the surface of 13762 rat mammary adenocarcinoma cells at approximately 100 times the level found in the lactating mammary gland. Immunocytochemical staining of SMC/Muc4 in the developing rat mammary gland is localized to the apical membrane of the ductal epithelium. This staining pattern is similar to that for peanut lectin, a differentiation marker, which binds to cells expressing the disaccharide Thomsen-Friedenreich or TF antigen. Blotting of glycoproteins expressing the TF antigen from mammary tissues with peanut lectin detects a protein matching the migration of ASGP-2. Analysis of immunoprecipitated SMC/Muc4 by peanut lectin blotting shows that the TF antigen is abundantly present on the ASGP-2 subunit, hence the similarity of staining pattern with SMC/Muc4 antisera and peroxidase-conjugated lectin in mammary tissues. The TF antigen is also present on ASGP-2 of SMC/Muc4 produced by confluent cultures of Rama 37 rat mammary epithelial stem cells after their induction to an alveolar-like phenotype with prolactin. These results indicate that the TF antigen is present on the ASGP-2 transmembrane subunit of SMC/Muc4 from phenotypically normal tissues and cells, in contrast to malignant cells whose peanut lectin-binding disaccharide is located on ASGP-1.
Li
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P
Department of Cell Biology and Anatomy (R-124), University of Miami School of Medicine, Miami, FL 33101, USA.
Price-Schiavi
S A
SA
Rudland
P S
PS
Carraway
K L
KL
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000648:ultrastructure; D019281:Dimerization; D005260:Female; D007150:Immunohistochemistry; D007774:Lactation / Q000502:physiology; D008321:Mammary Glands, Animal / Q000166:cytology* / Q000502:physiology; D055264:Mucin-4; D009077:Mucins / Q000032:analysis* / Q000737:chemistry; D019887:Peanut Agglutinin / Q000737:chemistry*; D049590:Postpartum Period / Q000502:physiology; D011247:Pregnancy; D021122:Protein Subunits; D051381:Rats; D011916:Rats, Inbred F344; D012795:Sialoglycoproteins / Q000032:analysis*
C524660:Muc4 protein, rat; D055264:Mucin-4; D009077:Mucins; D019887:Peanut Agglutinin; D021122:Protein Subunits; D012795:Sialoglycoproteins