RHAMM/hyaluronan inhibit ß-catenin degradation, enhance downstream signaling, and facilitate fibrosarcoma cell growth.

ABSTRACT

Increased hyaluronan deposition (HA) in various cancer tissues, including sarcomas, correlates with disease progression. The receptor for hyaluronic acid-mediated motility (RHAMM) expression is elevated in most human cancers. ß-catenin is a critical downstream mediator of the Wnt signaling pathways, facilitating carcinogenic events characterized by deregulated cell proliferation. We previously showed that low molecular weight (LMW) HA/RHAMM/ß-catenin signaling axis increases HT1080 fibrosarcoma cell growth. Here, focusing on mechanistic aspects and utilizing immunofluorescence and immunoprecipitation, we demonstrate that LMW HA treatment enhanced RHAMM intracellular localization (p ≤ 0.001) and RHAMM/ß-catenin colocalization in HT1080 fibrosarcoma cells (p ≤ 0.05). Downregulating endogenous HA attenuated the association of RHAMM/ß-catenin in HT1080 fibrosarcoma cells (p ≤ 0.0.01). Notably, Axin-2, the key ß-catenin degradation complex component, and RHAMM were demonstrated to form a complex primarily to cell membranes, enhanced by LMW HA (p ≤ 0.01). In contrast, LMW HA attenuated the association of ß-catenin and Axin-2 (p ≤ 0.05). The utilization of FH535, a Wnt signaling inhibitor, showed that LMW HA partially rescued the Wnt-dependent growth of HT1080 cells and restored the expression of Wnt/ß-catenin mediators, cyclin-D1 and c-myc (p ≤ 0.05). B6FS fibrosarcoma cells with different HA metabolism do not respond to the LMW HA growth stimulus (p = NS). The present study identifies a novel LMW HA/RHAMM mechanism in a fibrosarcoma model. LMW HA regulates intracellular RHAMM expression, which acts as a scaffold protein binding ß-catenin and Axin-2 at different cellular compartments to increase ß-catenin expression, transcriptional activity, and fibrosarcoma growth.