Impact of Heparan Sulphate Binding Domain of Chemokine CCL21 to Migration of Breast Cancer Cells

Abstract

Lymph node metastasis constitutes a key event in breast cancer progression. Chemokines are small proteins, which can promote metastatic spread by inducing cancer cell migration and invasion. Chemokine function is dependant upon their binding to both cell surface heparan sulphate (HS) molecules and to their specific receptor. Our group has demonstrated a significant increase in chemokine receptor CCR7 expression in cancerous breast epithelia compared to healthy controls. This study is designed to test the hypothesis that a non-HS binding forms of chemokine CCL21 can disrupt the normal response to CCL21, therefore reducing the metastasis of CCR7-expressing cancer cells. Truncated CCL21 chemokine (Δ98- 134 c-terminal basic extension), was synthesised to investigate a possible linkage between chemokine binding capacity and cell activation. Wild type (WT) and mutant-CCL21 were tested for their ability to stimulate a dose-dependent increase in intracellular-free calcium in peripheral blood mononuclear cell (PBMC) and breast cancer epithelial cells MDA-MB-231. Mutant-CCL21 at concentrations 5 and 10nM showed potential to mobilise Ca2+ at levels similar to that produced by WT-CCl21. A series of experiments was performed to determine how deletion of the HS-binding site altered the ability of CCL21 to stimulate chemotaxis within a concentration gradient generated by free solute diffusion. PBMC stimulated to migrate by wild-type CCL21 was not significantly different from that stimulated by mutant (P> 0.05). Similar results were observed in assays using MDA-MB-231 cells. A further series of experiments was performed to compare the potential of WT and mutant-CCL21 to stimulate the migration of cells across endothelium. In contrast to results for trans-filter migration, it was found that the non HSbinding mutant stimulated no increased in transendothelial cell migration above the background at each of the tested concentrations, 10, 30 and 50 nM respectively (P>0.05). However, WT-CCL21 stimulated significant increased PBMC migration at each of the tested concentration (all P <0.001). Furthermore, the effect of heparin on chemotactic properties of WT and mutant- CCL21 was examined. Interestingly, heparin (250 µg/ml) completely inhibit the chemotaxis mediated by WT-CCL21 (5nM) (P < 0.001), whereas it did not inhibit the chemotaxis at concentrations 100, 250 & 500 µg/ml in response to mutant CCL21 (5nM) (P > 0.05). Similar assay will be performed using MDA-MB-231 cells. Work is ongoing to characterise the biophysical properties of mutant-CCL21 and determine its potential role for a therapeutic blockade of the migration of breast cancer cells in-vivo. Our primarily data showed that mutant CCL21 in xenograft brain tumor models showed substantial inhibition of tumour growth. Our results indicate that truncated CCL21 chemokine might be a potential preventive biofactor for human breast cancer metastasis by targeting chemokine receptor genes.