Abstract 1868: Clinical significance of cathepsin L and B expression in pediatric acute myeloid leukemia

Abstract

Introduction: Cathepsin L and B are commonly expressed cysteine proteinases that play a major role in lysosomal bulk proteolysis, protein processing, matrix degradation, and tissue remodelling. In tumors there is deregulation of these proteases that interferes with these normal biological processes. In a pilot study done in our lab expression of cathepsin L and B were found to be significantly elevated in peripheral blood mononuclear cells (PBMCs) of pediatric AML patients. However the expression of these proteases in bone marrow aspirate, which represents almost true population of blasts, has never been studied before. Methods: Enzymatic activities of cathepsin L and B were assayed in PBMCs and bone marrow mononuclear cells (BMMCs) of AML patients and healthy controls. Further expression of these proteases and its inhibitor were confirmed by western blotting and real time assay. Cell cycle analysis in PBMCs and BMMCs of these patients was performed by flow cytometry using propidium iodide. Results: In the PBMCs of pediatric AML patients activity of cathepsin L and B was found to be significantly elevated as compared to healthy controls. Similarly, increased activity of cathepsin L and B was also observed in the BMMCs when compared with PBMCs of these patients. Furthermore, protein and mRNA expression also confirmed the increased level of these proteases in pediatric AML. The protein and mRNA expression of their endogenous inhibitor cystatin-C was found to be decreased in PBMCs and BMMCs of AML patients. Moreover, expression of these proteases correlated positively with the percentage of blasts and percentage of cells in S-phase. Conclusion: This study for the first time demonstrates the increased expression of cathepsin L and B in the BMMCs and PBMCs of pediatric AML patients, along with a positive correlation with percentage of blasts, thereby suggesting a potential role of these proteases in the severity of this disease.