Post-translational processing of the leukocyte integrin alpha 4 beta 1

• Published in: The Journal of biological chemistry Vol. 267; no. 35; pp. 25274 - 25281
• Main Authors: Bednarczyk, J L, Szabo, M C, McIntyre, B W
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 15.12.1992
• Subjects: Amino Acid Sequence; Antibodies, Monoclonal; Epitopes - analysis; Fibronectins - metabolism; Glycoside Hydrolases - antagonists & inhibitors; Humans; Immunoblotting; integrin; Integrin alpha4beta1; Integrins - biosynthesis; Integrins - genetics; Interleukin-2 - pharmacology; leucocytes; Leukocytes - physiology; Macromolecular Substances; Molecular Sequence Data; Peptides - chemical synthesis; Peptides - immunology; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protease Inhibitors - pharmacology; Protein Processing, Post-Translational; Receptors, Very Late Antigen - biosynthesis; Receptors, Very Late Antigen - genetics; T-Lymphocytes - drug effects; T-Lymphocytes - immunology; Tumor Cells, Cultured
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)74036-8

The leukocyte integrin alpha 4 beta 1 (VLA-4, CD49d/CD29) is a receptor for the extracellular matrix protein fibronectin and the endothelial adhesion protein VCAM-1. We have analyzed the biosynthesis and post-translational modifications of the two subunits of this receptor complex. The alpha 4 subunit was initially synthesized as a single-chain polypeptide that underwent the formation of complex endoglycosidase H-resistant oligosaccharide side chains and which could be proteolytically cleaved into two noncovalently associated fragments. The level and rate of alpha 4 subunit cleavage was dependent on the cell studied. The T cell tumor line HPB-ALL expressed both intact and fragmented alpha 4 on the cell surface. The interleukin-2-dependent natural killer line NK 3.3 and long term interleukin-2-dependent activated T lymphocytes cleaved the alpha 4 polypeptide earlier and more efficiently than did HPB-ALL cells and did not have detectable levels of intact alpha 4 on the cell surface. The proteolysis of alpha 4 was blocked by treating cells with either the lysosomotrophic amine NH4Cl or the carboxylic ionophore monensin. The presence of complex N-linked oligosaccharides did not seem to be necessary for alpha 4 cleavage or for binding of the alpha 4 beta 1 complex to a synthetic peptide corresponding to the binding site for this receptor on fibronectin.