Rhamm−/− fibroblasts are defective in CD44-mediated ERK1,2 motogenic signaling, leading to defective skin wound repair

Abstract

Rhamm (receptor for hyaluronan-mediated motility) is an hyaluronan binding protein with limited expression in normal tissues and high expression in advanced cancers. To understand its physiological functions and identify the molecular mechanisms underlying these functions, we created mice with a genetic deletion of Rhamm. We show that Rhamm−/− fibroblasts fail to resurface scratch wounds >3 mm or invade hyaluronan-supplemented collagen gels in culture. We identify a requirement for Rhamm in the localization of CD44 to the cell surface, formation of CD44–ERK1,2 (extracellular-regulated kinase 1,2) complexes, and activation/subcellular targeting of ERK1,2 to the cell nucleus. We also show that cell surface Rhamm, restricted to the extracellular compartment by linking recombinant protein to beads, and expression of mutant active mitogen-activated kinase kinase 1 (Mek1) are sufficient to rescue aberrant signaling through CD44–ERK1,2 complexes in Rh−/− fibroblasts. ERK1,2 activation and fibroblast migration/differentiation is also defective during repair of Rh−/− excisional skin wounds and results in aberrant granulation tissue in vivo. These results identify Rhamm as an essential regulator of CD44–ERK1,2 fibroblast motogenic signaling required for wound repair.

The Hyaluronan Receptors CD44 and Rhamm (CD168) Form Complexes with ERK1,2 That Sustain High Basal Motility in Breast Cancer Cells

“…For example, different CD44 protein forms may act as tumor suppressors during early stages of breast cancer; CD44std expression correlates positively with disease-related survival in node-negative invasive breast carcinoma (50) but acts as an enhancer of metastasis during later stages (88). Our results support a role for CD44 in aggressive functions of breast tumor cells when it is partnered with other motogenic proteins such as cell surface Rhamm (45).…”

“…CD44 was shown previously to promote motility of breast cancer cell lines, and Rhamm was shown to promote motility of fibroblasts and immune cells (9,45,65,71,72). Therefore, we compared the relative roles played by these HA receptors in the motility of the fibroblast-like MDA-MB-231 and Ras-MCF10A tumor cells with the epithelial MCF7 and MCF10A cells, using function-blocking antibodies specific to each of these receptors.…”

“…Importantly, cell surface Rhamm can additionally perform motogenic/invasive functions similar to CD44 and can even replace CD44 (46). These observations have raised the possibility that cell surface Rhamm may partner with CD44 to "unleash" its motogenic potential (45,46).…”

“…These include Ras (40), pp60-c-Src (44), and ERK1,2 (37). Cell surface Rhamm is required for sustained activation and intracellular targeting of ERK1,2 in dermal wound fibroblasts (45), suggesting that the extracellular Rhamm form could potentially function in tumor progression to increase the intensity and duration of signaling pathways associated with tumor invasion/motility. Importantly, cell surface Rhamm can additionally perform motogenic/invasive functions similar to CD44 and can even replace CD44 (46).…”

Adamts5 Deletion Blocks Murine Dermal Repair through CD44-mediated Aggrecan Accumulation and Modulation of Transforming Growth Factor β1 (TGFβ1) Signaling

“…It also appears to be required for MMP9-mediated activation of TGF␤1 (21). HA has been shown to ligate RHAMM to promote the association of CD44 and p-ERK, an interaction that directly activates cell migration and thereby is required for efficient dermal repair (22,23). HA also regulates the proliferative response of dermal fibroblasts to TGF␤1 (24), and HA12 oligosaccharides stimulate Col3 and TGF␤1 expression (25), a finding that is very relevant to the data described here.…”