Regulation of gastric cancer invasiveness by hyaluronic acid with specific molecular weight

Malignant cells are invasive due to their enhanced capability to migrate and high proliferation rate. [1] Cancer invasion and metastasis is linked to the formation of actin-rich membrane protrusions called invadopodia. [2] Their development is mediated by several proteins, such as, Tks5, Cortactin and neural Wiskott-Aldrich syndrome protein (N-WASP) [3], that compose the main core of the invadopodia. [4] Cortactin is overexpressed in several malignant cancer cells; it regulates the secretion of matrix metalloproteinases (MMPs) to the stubs of degrading invadopodia, i.e. it is crucial for the formation and function of invadopodia. [5] The cortactin expression is often concominant with the overexpression of the cell membrane receptor CD44. In fact, CD44 activates Src-kinase, a downstream effector that regulates the phosphorylation of cortactin and consequently, the formation of invadopodia. [6]

CD44 is also a main cell surface receptor for hyaluronic acid (HA) - glycosaminoglycan that is present in a variety of tissues. Herein we studied the influence of the molecular weight of HA on the expression of cortactin, the formation of invadopodia and, consequently, on the invasiveness of gastric cancer cells.

In this context, we used poly-L-lysine coated surfaces to electrostatically immobilize HA of different molecular weights (i.e. 1.5MDa, 752kDa and 6.4kDa) and tested these surfaces in direct contact with two gastric cell lines, namely AGS and MKN-45. The expression of CD44 was evaluated by flow cytometry and the expression of cortactin was analysed by immunocytochemistry. We observed that the expression of CD44 on both cell lines varies with the HA molecular weight, as follows: 6.4kDa £ 752kDa < 1500kDa. The same trend was observed for the cortactin. Our results suggest that the overexpression of CD44 on AGS and MKN-45, when in contact with HA with increasing molecular weight, induces the expression of cortactin and, consequently, increasing the CD44-mediated formation of invadopodia protuberances (possibly through the activation of Src-kinase), that should lead to the increase on the invasiveness of gastric cancer cells.

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