Induction of Human Prostate Cancer Cell Apoptosis by an IGFBP-3 Fragment

Diabetes, Digestive, Kidney Diseases

Investigators

Abstract

IGFBP-3 undergoes limited proteolysis by plasmin and other proteases to generate N-terminal fragments of approximately 97 amino acids that no longer bind IGFs but which still can inhibit cell proliferation. The present study examines whether an N-terminal 1-97 IGFBP-3 fragment can induce apoptosis in human prostate cancer cells in an IGF-independent manner. Plasmids expressing full-length IGFBP-3 or the 1-97 IGFBP-3 fragment fused to yellow fluorescent protein (YFP) were expressed in PC-3 human prostate cancer cells. Expression of either full-length IGFBP-3 or the IGFBP-3 fragment caused a loss of cell viability as determined by Annexin V staining and flow cytometry. Cell death was blocked by incubation with a caspase inhibitor, indicating that it resulted from apoptosis. Apoptosis also was induced when an additional mutation was introduced in the IGF-binding site of 1-97-IGFBP-3 so that it did not bind IGFs. These results show that the N-terminal IGFBP-3 fragment can induce apoptosis in human prostate cancer cells in an IGF-independent manner. Generation of the 1-97 fragment by limited proteolysis in vivo might contribute to the proapoptotic activity of IGFBP-3.