Functional measurement of local proteolytic activity in living cells of invasive and non-invasive tumors.

Abstract

Proteolytic cleavage of extracellular matrix (ECM) and disruption of tissue architecture are fundamental features of tumor cell invasion. The proteolytic activity is focused in close proximity to the tumor cells. Here, we describe the possibility to quantify local proteolytic activity in the microenvironment of larger cell populations by the electrical resistance breakdown assay. The assay utilizes the transepithelial electrical resistance (TEER) of an epithelial monolayer as a sensitive indicator of monolayer integrity and permeability. Local destruction of ECM by single tumor cells was demonstrated by a second assay, based on a fluorescent matrix coating on cover slides. Local digestion of the matrix results in a reduction of fluorescence. Primary cells derived from high and low grade brain tumors as well as established cell lines of malignant gliomas and non-neural tumors of different origin (melanoma, cervical carcinoma, and breast carcinoma) were compared. Differences in proteolytic activity between tumor entities were demonstrated in both assays. Primary cells of high grade gliomas and cell lines showed TEER breakdown and local matrix destruction, while low grade brain tumors lacked matrix disintegration and disruption of cell monolayers. Taken together, both assays are capable of demonstrating local proteolytic activity and thus are versatile tools for distinguishing high and low invasive tumor cells with a potential application as diagnostic and prognostic markers in clinical investigations. The advantage of the matrix digestion assay is the requirement of only very low tumor cell numbers, whereas measurement of TEER enables precise quantification of local proteolytic processes in large and even heterogeneous tumor cultures.