The role of hyaluronan and its CD44 receptor in inflammation and cancer

Abstract: Hyaluronan, an important extra-cellular matrix molecule, was thought to be interstitial connecting glue decades ago. However, recent evidence has revealed that hyaluronan and its binding proteins also play crucial roles in various pathophysiological conditions in humans, including inflammation and infection.Study I focused on dengue virus infection and found that elevated serum hyaluronan levels during early infection phase was an independent predictor for occurrence of warning signs, and thus severe dengue. High circulating levels of the viral non-structural protein 1 (NS1) correlated with high concentrations of serum hyaluronan. NS1 exposure decreased the expression of CD44 in differentiating endothelial cells impairing the integrity of vessel-like structures and promoted the synthesis of hyaluronan in dermal fibroblasts and endothelial cells in synergy with dengue-induced pro-inflammatory mediators. Perturbed hyaluronan-CD44 interactions enhanced endothelial permeability through modulation of VE-cadherin and cytoskeleton re-organization, and exacerbated the NS1-induced disruption of endothelial integrity. Study II reports a negative correlation between the expression of genes encoding hyaluronan synthase HAS2, its natural antisense transcript HAS2-AS, the chromatin modulating factor HMGA2 and transforming growth factor-β (TGFβ), and survival of patients with invasive breast cancer. TGFβ induction of Hmga2, Has2as and Has2 in mouse mammary epithelial cells, and synthesis of hyaluronan were accompanied with activation of Akt and Erk1/2 MAP-kinase signaling and were required for breast cancer cell motility. Importantly, the hyaluronan receptor Cd44, but not Hmmr, was required for TGFβ-mediated epithelial-mesenchymal transition phenotype. Has2as was found to contribute to the maintenance of stem cell factors and breast cancer stemness. Study III explored the physical interaction between the inhibitor of the apoptosis-stimulating protein of p53 (iASPP) and the hyaluronan receptor CD44. The CD44 standard isoform (CD44s), but not the variant isoform, bound to iASPP via the ankyrin-binding domain in CD44s. iASPP was required for hyaluronan-induced CD44-dependent migration and adhesion of fibroblasts. CD44 altered the sub-cellular localization of the iASPP-p53 complex; thus, ablation of CD44 promoted translocation of iASPP from the nucleus to the cytoplasm, resulting in increased formation of a cytoplasmic iASPP-p53 complex in fibroblasts. Overexpression of iASPP decreased the level of intracellular reactive oxygen species, while overexpression of CD44 increased. Knock-down of CD44s, in the presence of p53, led to increased cell growth and cell density of fibroblasts by suppression of p27 and p53.In summary, we investigated the interaction of hyaluronan and its transmembranous receptor, CD44, as well as the modulation of hyaluronan synthesis, in several different pathophysiological conditions.