Prohaptoglobin is proteolytically cleaved in the endoplasmic reticulum by the complement C1r-like protein
- 22 September 2004
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 101 (40), 14390-14395
- https://doi.org/10.1073/pnas.0405692101
Abstract
Many secretory proteins are synthesized as proforms that become biologically active through a proteolytic cleavage in the trans-Golgi complex or at a later stage in the secretory pathway. Haptoglobin (Hp) is unusual in that it is cleaved in the endoplasmic reticulum before it enters the Golgi. Here, we present evidence that the recently discovered complement C1r-like protein (C1r-LP) mediates this cleavage. C1r-LP has not previously been shown to possess proteolytic activity, despite its homology to trypsin-like Ser proteinases. We demonstrate that coexpression of the proform of Hp (proHp) and C1r-LP in COS-1 cells effected cleavage of proHp in the endoplasmic reticulum. This cleavage depended on proteolytic activity of C1r-LP because mutation of the putative active-site Ser residue abolished the reaction. Furthermore, incubation of affinity-purified C1r-LP and proHp led to the cleavage of the latter protein. ProHp appeared to be cleaved at the expected site because substitution of Gly for Arg-161 blocked the reaction. C1r-LP showed specificity for proHp, in that it did not cleave the proform of complement C1s, a protein similar to Hp particularly around the cleavage site. C1r-LP accounts for at least part of the endogenous proHp-cleavage activity because suppression of the C1r-LP expression by RNA interference reduced the cleavage of proHp by up to 45% in the cells of a human hepatoma cell line (HepG2).This publication has 27 references indexed in Scilit:
- The secretory proprotein convertase neural apoptosis-regulated convertase 1 (NARC-1): Liver regeneration and neuronal differentiationProceedings of the National Academy of Sciences of the United States of America, 2003
- Monomeric Structures of the Zymogen and Active Catalytic Domain of Complement Protease C1r: Further Insights into the C1 Activation MechanismStructure, 2002
- Structural biology of ClBiochemical Society Transactions, 2002
- Furin at the cutting edge: From protein traffic to embryogenesis and diseaseNature Reviews Molecular Cell Biology, 2002
- Intracellular Coupling of the Heavy Chain of Pre-α-inhibitor to Chondroitin SulfateOnline Journal of Public Health Informatics, 2002
- Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysisKidney International, 2000
- Proteolytic cleavage of haptoglobin occurs in a subcompartment of the endoplasmic reticulum: evidence from membrane fusion in vitro.The Journal of cell biology, 1993
- Complement genes C1r and C1s feature an intronless serine protease domain closely related to haptoglobinJournal of Molecular Biology, 1989
- Site-directed mutagenesis by overlap extension using the polymerase chain reactionGene, 1989
- Biosynthesis, intracellular processing and secretion of haptoglobin in cultured rat hepatocytesBiochemical and Biophysical Research Communications, 1983