Increased Furin Activity Enhances the Malignant Phenotype of Human Head and Neck Cancer Cells

Abstract

Many proteins are synthesized as inactive proforms requiring a proteolytic processing to render them active. A variety of proteases catalyze these cleavage reactions. Proprotein convertases are a family of serine proteases capable of activating substrates that will subsequently intervene in extracellular matrix (ECM) degradation, cell growth, differentiation and viral pathogenesis. Furin, the prototype of this family, has been implicated in many physiological and pathological processes. Some of its substrates such as TGF-␤, MT-MMP's, and IGFR-1 have been identified. Overexpression of furin has been observed in several human tumors. In this report we demonstrate that overexpression of furin causes a significant increase in the invasive potential of human tumor cells of low and moderate aggressive potential in vitro and in vivo. SCC12 and SCC15 were transfected with furin cDNA, resulting in efficient processing of furin substrates. An in vivo invasion assay showed enhancement of invasive ability. Inhibition of furin activity with the synthetic inhibitor decanoyl-Arg-Val-Lys-Argchloromethyl-ketone, CMK, showed a significant decrease in both processing and in vitro invasiveness. A moderate enhancement in proliferation rate was observed when cells were transfected with furin. CMK treatment resulted in a marked reduction of this effect. Tumors obtained after subcutaneous (s.c.) inoculation of furin-overexpressing cells were larger and developed earlier than the controls. Furin overexpression caused an imbalance in the activation of invasion and proliferation-related substrates leading to the acquisition of an advanced malignant phenotype. In addition, inhibition of furin activity decreases substrate activation, proliferation rate, and invasive potential of cancer cells, suggesting that furin is a potentially useful target for therapeutics.

Inhibition of Proprotein Convertases Enhances Cell Migration and Metastases Development of Human Colon Carcinoma Cells in a Rat Model

“…The reduced size of subcutaneous tumors in response to ␣1-PDX expression is likely due to differences in cell proliferation, as already reported in in vitro studies. [22][23][24] By histological staining with an antibody against Ki67, a nuclear protein expressed in proliferating cells, we confirmed that in situ cell proliferation was higher in PDX0-than in PDX39P-induced tumors (data not shown).…”

“…We, and others, previously observed that PCs inhibition leads to delayed tumor development and reduced tumor volume in nude or immunodeficient mice. [22][23][24][25] However, herein we used immunosuppressed newborn rats to test the metastatic dissemination. Results obtained with this animal model show that the role of PCs in tumor development and progression is far from being as simple as suggested by previous observations.…”

“…49 Differences in stromal microenvironment might thus explain the discrepancies between the present in vivo results and invasion assays using tracheal xenotransplants. 22,25 Given the role of PCs in biological activation of inactive precursors, their inhibition could be an interesting clinical strategy against cancers by simultaneously disrupting the function of numerous proteins involved in tumor cell invasion and tumor progression. 15,20 However, the effect of ␣1-PDX on certain convertase substrates, like adhesion molecules, MMPs or other proteases, that could potentially contribute to tumorigenesis should be taken into account when considering PC inhibitors as therapeutic tools for a variety of diseases, including cancer.…”

“…21 Moreover, further data show that tumors obtained after subcutaneous inoculation of furin-overexpressing cells are larger and develop earlier than the controls. 22 Conversely, inhibition of PCs resulted in reduced in vivo tumorigenicity and in vitro cell proliferation. [23][24][25] We have recently reported that the absence of endoproteolytic cleavage of ␣v integrins, by overexpression of ␣1-PDX in colonic cancer cells, has important consequences on signal transduction pathways leading to alterations in integrin function such as cell adhesion.…”

Matrix metalloproteases in head and neck cancer

“…12,[76][77][78] Increased activity of the MT1-MMP activator, furin, is associated with more aggressive in vitro and in vivo tumor activity in HNSCC. 79,80 In vitro and in vivo data similarly suggest that overexpression of MT1-MMP promotes HNSCC tumor cell invasion. 25,81 MT1-MMP plays a critical role in tumor cell invasion and angiogenesis through several known mechanisms: (1) activation of MMP-2, 77,82 (2) cleavage of the cell adhesion molecule CD44 from the cell surface, 83,84 (3) degradation of type I collagen and fibrin substrates, 29,85,86 and (4) enabling cell survival in three-dimensional matrices.…”