Matriptase Is Highly up-Regulated in Chronic Lymphocytic Leukemia and Promotes Cancer Cell Invasion

Abstract 4612

Proteases are known to play a critical role in cancer development and progression. Matriptase is an epithelial transmembrane serine protease essential for skin development and barrier function. Matriptase overexpression has been reported in many human solid tumors including prostate, breast, ovarian, kidney and lung cancers, indicating that matriptase may play an important role in cancer. In mice, dysregulated matriptase activity promotes malignant transformation and carcinogenesis.

In human blood, low levels of matriptase mRNA expression were detected in monocytes and B-lymphocytes but the biological significance is unclear. In this study, we examined matriptase mRNA and protein expression in 15 hematological cancer cell lines and 223 bone marrow samples from patients with leukemia by reverse transcription PCR (RT-PCR), quantitative real-time PCR (qRT-PCR) and Western blotting. Flow cytometry and immunostaining were used to determine the cell membrane expression of matriptase in B cell-derived Namalwa cells and bone marrow cells from leukemia patients. Small hairpin RNA (shRNA) interference and a recombinant matriptase inhibitor, hepatocyte growth factor activator inhibitor (HAI)-1, were used to inhibit matriptase expression and activity in Namalwa, Raji and chronic lymphocytic leukemia (CLL) cells to test the effect of matriptase inhibition on cancer cell invasion in matrigel-based assays.

Our results showed that matriptase mRNA was highly expressed in Namalwa and Raji cells and in bone marrow cells from patients with CLL. Such an expression profile was not found in bone marrow cells from patients with acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). By Western blotting, matriptase protein expression was confirmed in bone marrow samples from the majority (79/81, 97.5%) of CLL patients. By immunostaining and flow cytometry, matriptase protein was localized on the surface of Namalwa and CLL cells. In these cells, the matriptase inhibitors, HAI-1 and HAI-2, were not detected, indicating that the upregulated matriptase activity may not be inhibited in CLL cells. In functional studies, silencing matriptase gene expression by specific shRNAs markedly reduced Namalwa and Raji cells and bone marrow cells from CLL patients in invading matrigels. Similarly, a recombinant HAI-1 dose-dependently inhibited matrigel invasion of these cancer cells.

In conclusion, our results showed that matriptase was highly expressed on the surface of CLL cells. Inhibition of matriptase by gene silencing or specific inhibitor prevented CLL cells in invading matrigels, indicating that matriptase contributes to the invasiveness of the cancer cells. Our results suggest that matriptase may represent a new cell surface marker for CLL and that blocking matriptase expression or activity may be used as a therapeutic strategy to inhibit CLL progression.