Role of sparc and MIR-29B1 in molecular effects induced by win in osteosarcoma MG63 cells

Abstract

SPARC (Secreted protein acidic and rich in cysteine) is considered as a prototype of matricellular protein due to its structure and the function that it displays in regulating cell/extracellular microenvironment interactions during development and in response to injury. Earlier studies underlined pleiotropic effects of intracellular SPARC on cancer growth and, in some cancer cell lines, identified it as a tumor suppressor protein. Objective This study aimed to evaluate the role of SPARC and its related miRNA in the molecular effects induced by the cannabinoid WIN in osteosarcoma MG63 cells. In these cells WIN is not able to induce cell death but sensitizes cells to TRAIL-mediated apoptotic extrinsic pathway. Methods Western blotting analysis and qRT-PCR were employed to evaluate the expression level of SPARC and miR-29b1. Wound healing assay and zymography were employed to evaluate the migratory ability of cells. Results and Conclusions In MG63 cells WIN (5 μM) induces a dose- and time-dependent increase in the level of SPARC. Immunoprecipitation experiments showed that SPARC links caspase-8 and is responsible for its translocation and activation on plasma membrane. In this way, SPARC sensitizes osteosarcoma cells to WIN/TRAIL cytotoxic effects, as supported by SPARC silencing experiments. Moreover, we demonstrated that SPARC is not involved in migratory ability of MG63 cells, thus indicating that SPARC has a specific intracellular action as tumor suppressor. The analysis of miR-29 family cluster demonstrated that WIN induces a 300-fold increase of miR-29b1, the specific regulator of SPARC expression. Although a canonical relationship between miR-29b and SPARC can be excluded, the miR-29b1 overexpression seems, indeed, to be involved in the blocking of WIN-dependent cell migration, as demonstrated in transfected cells stably overexpressing miR-29b1. Studies are in progress to identify the cellular targets and mechanism of action of this miRNA.