Biological function analysis of monoclonal antibodies against human granulins in vitro using U251 cells as a model.

Progranulin (PGRN), a highly glycosylated, secreted 593 amino acid precursor protein, is a multifunctional molecule that is critical for early embryogenesis, wound repair, inflammatory and tumorigenesis. PGRN can be proteolytically cleaved into seven cysteine-rich granulin (Grn) peptides: G, F, B, A, C, D and E. Both PGRN and its constituent Grn peptides have been implicated in a wide variety of biological activities. However, their functions are far from clear, and the lack of granulin domain-specific antibodies has hindered the progress of the functional study of PGRN and Grns. Monoclonal antibodies against GrnB, GrnA, GrnC and GrnF have been previously developed by our laboratory. In this study, we generated monoclonal antibodies (MAbs) against GrnD, GrnG and GrnE by using recombinant proteins HSA-GrnG, HSA-GrnD and HSA-GrnE as immunogens, and characterized them by indirect ELISA, Western blot and immunocytochemistry. Furthermore, the neutralizing activities of the MAbs against seven Grns were tested in vitro using the U251 cell line. This full antibody panel of MAbs against seven Grns will be a valuable tool for elucidating the biological roles of PGRN and Grns in different physiopathological processes, which will further promote the development of PGRN-based clinical diagnosis and therapy.