Molecular flexibility of hyaluronic acid has a profound effect on invasion of cancer cells.

Extracellular hyaluronic acid (HA) has been shown to be important in cancer; low-molecular-weight HA typically correlates with cancer progression, high-molecular-weight HA with homeostasis. Here we show that even high-molecular-weight HA can induce cancer cell migration when it is highly diluted. HA-induced cell signalling is primarily through HA binding to the cell surface receptor, CD44. We show by NMR spectroscopy that at high dilution, high-molecular-weight HA molecules access the conformations needed for strong binding to CD44 on the tens of nanosecond time scale, the relevant time scale for induction of CD44 signalling. We further show that, by contrast, at higher concentrations, high-molecular-weight HA molecules have insufficient flexibility for strong CD44 binding. The high dilution HA condition correlates with profound changes in brain cancer cell morphology and proteome which supports cancer cell invasion. We hypothesize that the flexibility of HA molecules is central to HA-mediated cell signalling and that this concept can explain previous observations that the outcome of HA-mediated signalling depends on the HA molecular weight. HA dilution leading to stronger HA signalling may be important in understanding the role that oedema plays in cancer recurrence after primary surgery.