title: Regulation of C1q receptor expression on human polymorphonuclear leukocytes.
abstract: The C1q receptor (C1qR) is expressed on a variety of cells, including polymorphonuclear leukocytes (PMN), in which stimulation by the C1qR leads to activation as measured by superoxide production. To investigate the expression and modulation of the C1qR on PMN, the binding of biotinylated C1q to PMN in suspension was measured by flow cytometry. Biotinylated C1q bound in a saturable and specific manner to PMN and the use of low ionic strength buffers enhanced binding. Covalent coupling of C1q to Sepharose beads allowed the affinity precipitation of a single 125-kDa band from surface iodinated PMN. The apparent molecular mass of the C1qR increased to 135 kDa upon reduction. Freshly isolated PMN had a uniform expression of C1qRs and phorbol myristate acetate induced a unimodal up-regulation of receptors. The inflammatory peptide FMLP rapidly up-regulated receptors by up to fivefold, and the high level of expression remained constant over 45 min. Taxol inhibited the FMLP induction of C1qR up-regulation, indicating that the ability to move the intracellular stores of C1qR depends on normal microtubule functioning. Thus, the C1qR is a constitutively expressed protein of the human PMN plasma membrane and it is rapidly up-regulated from a discrete intracellular pool of preformed molecules with the same kinetics as CR1 and CR3. It is likely that the C1qR is a component of the PMN complement receptor exocytic vesicle (CREV), in which CR1 and CR3 are also stored.
authors.affiliation: Department of Rheumatology and Immunology, Brigham and Women's Hospital, Boston, MA.
authors.forename: R M
authors.initials: RM
authors.lastname: Jack
authors.forename: B A
authors.initials: BA
authors.lastname: Lowenstein
authors.forename: A
authors.initials: A
authors.lastname: Nicholson-Weller
mesh_terms: D002352:Carrier Proteins; D002462:Cell Membrane / Q000378:metabolism; D015922:Complement C1q / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D008970:Molecular Weight; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D017239:Paclitaxel / Q000494:pharmacology; D011951:Receptors, Complement / Q000737:chemistry / Q000378:metabolism*; D017463:Receptors, Complement 3b / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015854:Up-Regulation
chemical_list: C087299:C1QBP protein, human; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; D017463:Receptors, Complement 3b; C032402:complement 1q receptor; D009240:N-Formylmethionine Leucyl-Phenylalanine; D015922:Complement C1q; D013755:Tetradecanoylphorbol Acetate; D017239:Paclitaxel