Dr. Liza Barki-Harrington
Department of Human Biology
Our Goal We combine advanced biochemical approaches (e.g. MS/MS) with molecular biology techniques (e.g. CRISPR/Cas9) in both cell cultures and animal/human tissues to investigate the mechanisms that lead to COX-2 limited proteolysis as well pathways that lead to its removal from the cell. Main Research Activities Novel pathways that lead to elimination of COX-2 from the cell. We recently demonstrated that in addition to degradation in the cellular proteasome, COX-2 is secreted into the extracellular media packed in exosomes. This process is further enhanced by stimulating enzymatic activity by exposing the enzyme to its substrate arachidonic acid (AA), suggesting that secretion of AA-activated COX-2 constitutes a means to remove damaged inactive COX-2 from the cell. Limited proteolysis of COX-2 enhances cell proliferation. We recently demonstrated that COX-2 appears to be cleaved into distinct fragments in mouse and human tumors, and that a mutation at the carboxyl-terminus of COX-2 causes the appearance of several COX-2 immunoreactive fragments in nuclear compartments, and significantly enhances cell proliferation. We are currently focusing on the following: 1) Identifying the cleavage sites of COX-2 in endogenous systems; 2) Identifying the signals that cause COX-2 proteolysis; 3) Discovering the identity of the proteases that cleave COX-2; 4) Identifying the cellular pathways that are affected by COX-2 fragments and 5) Determining the presence of specific COX-2 fragments in mouse and human tumors. Role of site-1 protease in cell proliferation. Endogenous knockout of the gene for Site-1 protease in a colon-cancer-derived cell line causes a dramatic growth retardation. We have analyzed the transcriptome of this manipulated line and studying the pathways that are involved in its effect on cell growth with the intention of identifying possible drug targets to inhibit colon cancer proliferation. The role of COX-2 proteolysis by site 1 protease is at the focus of our examination.