Glycosylation of CD44 negatively regulates its recognition of hyaluronan.

Abstract

SummaryAlthough CD44 is expressed on a wide variety of cell types, few of them use it to recognize the ligand hyaluronan (HA). A glycosylation-defective clone of Chinese hamster ovary cells (Lec 8) bound HA, demonstrating that complete processing of glycoproteins with addition of a full complement of sialic acid is not required. On the contrary, subsequent findings revealed that complex sugars on CD44 can actually inhibit ligand recognition. Two subclones of wild-type Chinese hamster ovary cells with similar amounts of surface CD44 were isolated on the basis of HA binding and found to differ with respect to CD44 size as well as staining with fluorescent lectins. Treatment of the nonbinding clone with tunicamycin reduced the size of the protein and allowed the cells to recognize HA via CD44. This function was also induced by treatment with deglycosylating enzymes (either a mixture of endoglycosidase F and N-glycosidase F or neuraminidase alone). A possible role for glycosylation in regulation of adhesion was then sought with a series of normal and transformed murine cells. Disruption of glycosylation or treatment with deglycosylating enzymes did not induce ligand binding in an interleukin 7-dependent pre-B cell line, and splenic B cells also appeared to be in an inactive state. Some normal B cells acquired the ability to recognize HA after stimulation with lipopolysaccharide or interleukin 5 and had distinctive surface characteristics (loss of immunoglobulin D and acquisition of CD43). An additional subset of activated cells might have been in a transitional state, because the cells bound ligand after neuraminidase treatment. The ligand-binding ability of a purified CD44-immunoglobulin fusion protein dramatically increased after neuraminidase treatment. Thus, differential glycosylation of this molecule is sufficient to influence its recognition function. Cell adhesion involving HA can be regulated by multiple mechanisms, one of which involves variable glycosylation of CD44.

CD44 in hematological neoplasias

“…Thereby HA fulfills a passive 'linking' function between CD44 expressing cells as well as signal transduction [2,13]. The binding activity of HA to CD44 in general displays a great variability dependent on CD44 surface expression and clustering [26], insertion of variant exons in the CD44 molecule [6], and post-translational modifications of CD44 [among others [27,28] and can be regulated by cytokines. CD44/HA signaling itself can be affected by the molecular weight of HA e.g.…”

Differential expression of CD44 splice variants in the normal human central nervous system

“…In addition, variations in glycosylation contribute to structural and functional diversity of CD44 Ž . Katoh et al, 1995;Lesley et al, 1995 . Standard CD44 Ž .…”

“…Finally, it has been described that the hyaluronate-binding capacity of CD44 is dependent on the glycosylation of the CD44 Ž . molecule Katoh et al, 1995;Lesley et al, 1995 . Differential glycosylation of CD44 molecules, which is likely to Ž occur in the CNS Sano et al, 1993;Hoffmann et al, .…”

Role of sialidase in Mycoplasma alligatoris-induced pulmonary fibroblast apoptosis

“…Mycoplasmal viability was confirmed by culture on agar at the end of the incubation period, and the identity of the mycoplasmas recovered was confirmed by 16S rDNA PCR-RFLP. Uninfected control cultures were incubated with 100 mU/ml C. perfringens sialidase (Katoh et al, 1995;Lesley et al, 1997), or with DANA, then analyzed by fluorescence imaging and flow cytometry as described below.…”

“…Sialidase can unmask the CD44 molecules which are present on the surface of most host cells, but prohibited from binding HA by sialylation (Bartolazzi et al, 1996;Gee et al, 2004;Katoh et al, 1995). Following CD44 desialylation, binding of low molecular weight HA fragments from ECM degraded by hyaluronidase (Gee et al, 2004;Lesley et al, 1997) initiates intracellular signaling by CD44 through networks leading to production of pro-inflammatory cytokines (Sague et al, 2004), synthesis of cytotoxic nitric oxide (Iacob and Knudson, 2005), and inappropriate apoptosis involving the "fibroblast-associated" (Fas) receptor CD95-mediated signal transduction pathway (Fujii et al, 2001;Menaker and Jones, 2003).…”