The large subunit of replication factor C is a substrate for caspase-3 invitro and is cleaved by a caspase-3-like protease during Fas-mediated apoptosis

Abstract

Caspase‐3 is an ICE‐like protease activated during apoptosis induced by different stimuli. Poly(ADP‐ribose) polymerase (PARP), the first characterized substrate of caspase‐3, shares a region of homology with the large subunit of Replication Factor C (RF‐C), a five‐subunit complex that is part of the processive eukaryotic DNA polymerase holoenzymes. Caspase‐3 cleaves PARP at a DEVD‐G motif present in the 140 kDa subunit of RF‐C (RFC140) and evolutionarily conserved. We show that cleavage of RFC140 during Fas‐mediated apoptosis in Jurkat cells and lymphocytes results in generation of multiple fragments. Cleavage is inhibited by the caspase‐3‐like protease inhibitor Ac‐DEVD‐CHO but not the caspase‐1/ICE‐type protease inhibitor Ac‐YVAD‐CHO. In addition, recombinant caspase‐3 cleaves RFC140 in vitro at least at three different sites in the C‐terminal half of the protein. Using amino‐terminal microsequencing of radioactive fragments, we identified three sites: DEVD⁷²³G, DLVD⁹²²S and IETD¹¹¹⁷A. We did not detect cleavage of small subunits of RF‐C of 36, 37, 38 and 40 kDa by recombinant caspase‐3 or by apoptotic Jurkat cell lysates. Cleavage of RFC140 during apoptosis inactivates its function in DNA replication and generates truncated forms that further inhibit DNA replication. These results identify RFC140 as a critical target for caspase‐3‐like proteases and suggest that caspases could mediate cell cycle arrest.