Two Novel Functions of Hyaluronidase-2 (Hyal2) Are Formation of the Glycocalyx and Control of CD44-ERM Interactions

Abstract

It has long been predicted that the members of the hyaluronidase enzyme family have important non-enzymatic functions. However, their nature remains a mystery. The metabolism of hyaluronan (HA), their major enzymatic substrate, is also enigmatic. To examine the function of Hyal2, a glycosylphosphatidylinositol-anchored hyaluronidase with intrinsically weak enzymatic activity, we have compared stably transfected rat fibroblastic BB16 cell lines with various levels of expression of Hyal2. These cell lines continue to express exclusively the standard form (CD44s) of the main HA receptor, CD44. Hyal2, CD44, and one of its main intracellular partners, ezrin-radixin-moesin (ERM), were found to co-immunoprecipitate. Functionally, Hyal2 overexpression was linked to loss of the glycocalyx, the HA-rich pericellular coat. This effect could be mimicked by exposure of BB16 cells either to Streptomyces hyaluronidase, to HA synthesis inhibitors, or to HA oligosaccharides. This led to shedding of CD44, separation of CD44 from ERM, reduction in baseline level of ERM activation, and markedly decreased cell motility (50% reduction in a wound healing assay). The effects of Hyal2 on the pericellular coat and on CD44-ERM interactions were inhibited by treatment with the Na ؉ /H ؉ exchanger-1 inhibitor ethyl-N-isopropylamiloride. We surmise that Hyal2, through direct interactions with CD44 and possibly some pericellular hyaluronidase activity requiring acidic foci, suppresses the formation or the stability of the glycocalyx, modulates ERMrelated cytoskeletal interactions, and diminishes cell motility. These effects may be relevant to the purported in vivo tumorsuppressive activity of Hyal2.

Reactive Oxygen Species and Hyaluronidase 2 Regulate Airway Epithelial Hyaluronan Fragmentation

“…Specifically in sheep airway epithelium, GPI-anchored Hyal2 function as a receptor for oncovirus such as Jaagsiekte retrovirus and enzootic nasal tumor virus (64). Recently, roles in the formation of the glycocalyx and control of CD44-ERM (ezrin-radixin-moesin) interactions have been described (65). Such non-enzymatic functions were not explored in the current work.…”

A mammalian homolog of the zebrafish transmembrane protein 2 (TMEM2) is the long-sought-after cell-surface hyaluronidase

“…Interestingly, Harada and Takahashi (32) reported that HYAL2, a GPI-anchored molecule that is localized intracellularly when transfected alone into 293T cells, is translocated to the cell surface upon co-transfection of CD44, suggesting the possibility that it may act as a cell-surface hyaluronidase in the presence of CD44. Still, in view of a number of conflicting data regarding its pH optimum (9,(32)(33)(34) and subcellular localization (9,(33)(34)(35)(36), the significance of HYAL2 as a cell-surface hyaluronidase is far from clear. Two other HYAL family molecules, PH-20/SPAM1 and HYAL5, are active in near neutral pH and can degrade HA in the extracellular environment (12,37).…”

Interleukin-1β-induced Reduction of CD44 Ser-325 Phosphorylation in Human Epidermal Keratinocytes Promotes CD44 Homomeric Complexes, Binding to Ezrin, and Extended, Monocyte-adhesive Hyaluronan Coats

“…The ability of CD44 to bind hyaluronan is influenced by alternative splicing and post-translational modifications as described above (1). Furthermore, attachment of CD44 to actin cytoskeleton through the ezrin-radixin-moesin (ERM) 3 family of linker proteins (17)(18)(19) or to receptors that activate cytoplasmic signaling (20) may modulate hyaluronan binding. * This work was supported by grants from the Juselius Foundation (to R. T. and M. T.), the Cancer Center of the University of Eastern Finland (to R. T. and M. T.), the Saimaa Cancer Foundation (to S. O), and Special Government Funding of Kuopio University Hospital (M. T.).…”