Interaction of tissue plasminogen activator inhibitor with cell surface guanidinobenzoatase and urokinase plasminogen activator

This study employs fluorescent inhibitor molecules to detect both cell surface proteases and their receptor sites on colonic carcinoma cells. Present studies are concerned with the interactions of the tumour associated proteases, guanidinobenzoatase (GB) and plasminogen activators (PAs) with PAs inhibitor type 1 (PAI-1). The active enzymes on the cell surfaces in frozen sections of human colonic carcinoma tissue were located by staining with two active site directed fluorescent inhibitors, 9-aminoacridine (9-AA) and Rhodamine labelled PAI-1 (Rh-PAI-1), followed by fluorescence microscopy. Fibrin treated sections, which now lack GB but have receptor proteins for GB, fail to bind 9-AA and Rh-PAI-1. When these fibrin-treated sections were incubated with purified colonic carcinoma GB and u-PA, both enzymes were bound to the tumour cells in these sections and subsequent challenging with fluorescent probes for GB resulted in bright fluorescence under appropriate microscopic conditions. On the other hand when fibrin treated sections were incubated with t-PA, followed by challenging with Rh-PAI-1, no red fluorescence was observed. It is suggested that the GB and u-PA have similar specific binding sites which can recognise and bind to the receptors on tumour cells in fibrin-treated sections, but t-PA has no such binding site and fails to recognise the cell surface receptors for GB. These GB-receptors may have a possible role in the regulation of GB and u-PA activity during tumour cell invasion and metastasis.