Regulation of CD44 binding to hyaluronan by glycosylation of variably spliced exons.

Journal article

The hyaluronan (HA)-binding function (lectin function) of the leukocyte homing receptor, CD44, is tightly regulated. Herein we address possible mechanisms that regulate CD44 isoform-specific HA binding. Binding studies with melanoma transfectants expressing CD44H, CD44E, or with soluble immunoglobulin fusions of CD44H and CD44E (CD44H-Rg, CD44E-Rg) showed that although both CD44 isoforms can bind HA, CD44H binds HA more efficiently than CD44E. Using CD44-Rg fusion proteins we show that the variably spliced exons in CD44E, V8-V10, specifically reduce the lectin function of CD44, while replacement of V8-V10 by an ICAM-1 immunoglobulin domain restores binding to a level comparable to that of CD44H. Conversely, CD44 bound HA very weakly when exons V8-V10 were replaced with a CD34 mucin domain, which is heavily modified by O-linked glycans. Production of CD44E-Rg or incubation of CD44E-expressing transfectants in the presence of an O-linked glycosylation inhibitor restored HA binding to CD44H-Rg and to cell surface CD44H levels, respectively. We conclude that differential splicing provides a regulatory mechanism for CD44 lectin function and that this effect is due in part to O-linked carbohydrate moieties which are added to the Ser/Thr rich regions encoded by the variably spliced CD44 exons. Alternative splicing resulting in changes in protein glycosylation provide a novel mechanism for the regulation of lectin activity.

Authors: Bennett, K; Modrell, B; Greenfield, B; Bartolazzi, A; Stamenkovic, I

• Publication status: Published
• Journal: Journal of cell biology
• Volume: 131
• Issue: 6 Pt 1
• Pages: 1623-1633
• Publication date: 1995-12-01
• DOI: 10.1083/jcb.131.6.1623
• EISSN: 1540-8140
• ISSN: 0021-9525
• Language: English
• Keywords: Base Sequence; Alternative Splicing; Hyaluronic Acid; Humans; Carbohydrate Metabolism; Exons; Glycosylation; Antigens, CD44; Lectins; Tumor Cells, Cultured; Melanoma; Molecular Sequence Data