In vitro biosynthesis of complement factor I by human endothelial cells

Abstract

We have studied the secretion of the complement regulatory protein factor I by human umbilical vein endothelial cells (HUVEC). Northern and Western blot analysis and biosynthetic labeling experiments indicate that HUVEC secrete factor I at very low levels in basal conditions and that this secretion is significantly enhanced by interferon-gamma. Analysis of the proteolytic inactivation of C3b by HUVEC supernatants show that factor I is secreted in a functional form and can promote the specific proteolytic inactivation of C3b to iC3b. Together with previous studies establishing the secretion of complement factor H by HUVEC, this work demonstrates that the endothelial cell is able to secrete in its environment two complement regulatory proteins, factor I and factor H, which can mediate the degradation of C3b to iC3b. The secretion of factor I by HUVEC provides a useful in vitro model to analyze the modulation of this secretion and may be relevant to the local deposition of iC3b at the surface of the endothelium during the inflammatory reaction.

Local and systemic activationofthe whole complement cascade in human leukocytoclastic cutaneous vasculitis; C3d,g and terminal complement complex as sensitive markers

“…and CD59 [ 15] and plastna regulatory proteins factor H. factor 1. vitronectin and clusterin. Factor H and factor 1 were also found to be secreted by endothelial cells [26][27][28], Thus, the presence in LCV perivascular deposits of C3d,g and clustcrin-associatcd TCC. which are products of C3b and TCC inactivation respectively, emphasizes the fact that membrane-bound and/or plasma regulatory proteins may adequately fulfil their control role.…”

The molecular basis of hereditary complement factor I deficiency.

“…Proteins synthesized by primary cultures of fibroblasts were radiolabeled as previously described (4). Briefly, confluent monolayers of fibroblasts or Hep G2 cells in 75-cm 2 flasks were stimulated with gamma-interferon (500 U/ml) for 24 h. After washing twice with HBSS, cultures were incubated for 6 h with 6 ml of DME/20% FCS in the absence of glutamine, methionine or cystine (ICN Biomedicals Ltd., Thame, Oxfordshire, U.K.) supplemented with 1 mCi [ 35 S]methionine (Tran 35 S Label; ICN Biomedicals Ltd., Thame, Oxfordshire, U.K.).…”

“…Four basic amino acids are then excised from the precursor prior to secretion of the heterodimer. FI synthesis has also been demonstrated in vitro by primary monocyte cultures (3), endothelial cells (4), and by the Raji B cell line (5).…”

Analysis of Binding Sites on Complement Factor I Using Artificial N-Linked Glycosylation

“…FI is produced mainly in the liver but also by monocytes (14), fibroblasts (15), keratinocytes (16), and endothelial cells (17). It is synthesized as a single polypeptide chain of 66 kDa and N-glycosylated at six positions (25-27%, w/w) with heavily sialylated biantennary glycans (18).…”