Produção recombinante e estudos funcionais de três novas cistatinas da cana-de-açúcar e sua utilização em estudos de inibição da adesão, proliferação, migração e invasão celular
ABSTRACT Tumor metastasis is usually a major cause of death among cancer patients. Degradation and invasion of the extracellular matrix and basement membrane, key steps in the metastatic process, rely on the activity of proteolytic enzymes. The levels and activities of cathepsins B and L are considerably increased in cancer cells, and have been related to the invasive potential of these cells. Moreover, the levels of their endogenous inhibitors, the cystatins, are decreased, which results in an imbalance that contributes to the development of the metastatic phenotype. Thus, the potential use of cystatins as therapeutic agents in novel anti cancer strategies has been suggested. The sugarcane genome project (SUCEST FAPESP) allowed the identification of about 20 putative cystatins in this plant. In the present study, we describe the heterologous expression, purification and characterization of three cystatins from sugarcane, dubbed as CaneCPI-2, CaneCPI-3 and CaneCPI-4, which showed different inhibitory activities against human cathepsins B and L. While the three recombinant cystatins inhibited cathepsin L activity with Ki values of 0.17, 0.6 and 0.021 nM, respectively, only CaneCPI-4 was capable of efficiently inhibiting cathepsin B activity (Ki = 0.83 nM). Considering the involvement of these cathepsins in tumor cell invasion, the effect of the cystatins on the invasive ability of human breast cancer MDA-MB-231 cells was assessed after the addition of the recombinant cystatins to the cells, and in cell clones expressing the sugarcane cystatins. Overall, the Ki values correlated with the ability of the cystatins to inhibiting the cysteine cathepsin activity of the tumor cells as well as the cell invasion through a Matrigel matrix. A slight reduction in the invasive ability was observed in the MDA-MB-231 cells expressing CaneCPI-4. In addition, a substantial reduction of ~ 60% in the cell invasion was obtained in the presence of 2 µM recombinant CaneCPI-2 or CaneCPI- 3, or 0.2 µM of CaneCPI-4. Finally, the cystatins showed negligible effects on the adhesion and proliferation of the cells. Our results open the possibility of considering these as well as other phytocystatins as therapeutics agents in anti-cancer strategies.