Colocalization of basic fibroblast growth factor and CD44 isoforms containing the variably spliced exon v3 (CD44v3) in normal skin and in epidermal skin cancers

Abstract

Previous in vitro studies have shown CD44 isoforms containing the alternatively spliced exon v3 (CD44v3) to be modified with heparan sulphate (HS) and to bind HS-binding basic fibroblast growth factor (bFGF). Here, we demonstrate that exogenously added bFGF is also bound in vivo by CD44v3-positive keratinocytes in normal skin and by tumour cells in basal cell carcinoma and squamous cell carcinoma (SCC), two skin cancers of keratinocyte origin. bFGF binding and CD44v3 expression were colocalized in cultured human normal keratinocytes (HNK) and on the SCC cell line A431. By contrast, benign or malignant tumours of melanocyte origin failed to express CD44v3 and bound no bFGF. The bFGF binding to normal or transformed keratinocytes in vivo and in vitro was dependent on HS modification, as it was completely eliminated by pretreatment with heparitinase or by blocking with free heparin, whereas chondroitinase had no effect. In addition, specific removal of CD44v3 by antibody-induced shedding also diminished bFGF binding to keratinocytes. Furthermore, bFGF stimulated the proliferation of CD44v3-positive HNK and A431 in a dose-dependent fashion. This bFGF effect was again completely abolished by heparitinase or free heparin, but not by chondroitinase. In aggregate, our results suggest that a function of HS-modified CD44 isoforms such as CD44v3 in skin is to present the HS-binding growth factor bFGF, thereby stimulating the proliferation of normal or transformed keratinocytes.

Fibroblast growth factor-binding protein expression changes with disease progression in clinical and experimental human squamous epithelium

“…FaDu cells were used as positive controls for the FGF-BP MAb 17 and A431 cells, for the bFGF MAb. 27 Both are SCC cell lines known to express the respective proteins. Tissue sections without primary antibody were used as negative controls.…”

Hyaluronan-CD44 Interaction with Rac1-dependent Protein Kinase N-γ Promotes Phospholipase Cγ1 Activation, Ca2+ Signaling, and Cortactin-Cytoskeleton Function Leading to Keratinocyte Adhesion and Differentiation

“…CD44v3 and CD44v10) in addition to CD44s and CD44v3-10 (Epican) (6 -12). These CD44 isoforms have the same amino acid sequences at the two ends of the molecule but differ within the CD44 membrane-proximal region located at the external side of the membrane (5)(6)(7)(8)(9)(10)(11)(12). Different CD44 isoforms are also further modified by extensive N-and O-glycosylations and glycosaminoglycan additions (13)(14)(15).…”

“…The predominant receptor for HA on the cell surface of keratinocytes is CD44 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12). CD44 is encoded by a single gene that contains 19 exons (5).…”

A mutation in a CD44 variant of inflammatory cells enhances the mitogenic interaction of FGF with its receptor

“…Because exon v3 of the CD44 proteoglycan is the only one containing this sequence in the context of the SG or SGSG motif, HS assembly is confined to this exon (30). The sequestering of HS-binding growth factors on the v3 exon of CD44 proteoglycan has been well documented (5)(6)(7)(8)(9)(10)(11)(12). Moreover, Sherman and colleagues (12) demonstrated that the addition of anti-CD44v3 mAb to limb bud mesenchymal cells cocultured in the presence of FGF-8, with UV-irradiated Namalwa cells expressing CD44v3-v10, markedly reduced the proliferation of the FGFR-bearing mesenchymal cells.…”

“…CD44 proteoglycans can immobilize HS-binding growth factors, such as hepatocyte growth factor/scatter factor (5-7), VEGF (8), and heparin-binding epidermal growth factor (8)(9)(10), as well as FGF-2 (also known as basic FGF) (8,9,11), , and FGF-8 (12). Previous studies on the mode of action of FGF-2 and its association with HS identified a novel role for cell surface-and ECM-resident HS molecules in the formation of distinct FGF-2-HS complexes that are essential for binding FGF-2 to its cognate receptor (13) and subsequent signal transduction (14,15).…”