title: Localization of P32 protein (gC1q-R) in mitochondria and at specific extramitochondrial locations in normal tissues.
abstract: P32 protein, also known as the gC1q receptor for complement component C1q, is a binding protein for nuclear pre-mRNA splicing factor SF2/ASF and numerous other nuclear and cell surface proteins, yet is targeted to the mitochondrial matrix compartment where these proteins are not present. In the present study, we use immunogold electron microscopy to evaluate the subcellular distribution of P32 protein (gC1q-R) in cultured cell lines and in rat tissues embedded in the acrylic resin LR Gold. Immunogold labeling of Raji lymphoma, CHO, human fibroblasts, HeLa and B-SC-1 cells shows reactivity primarily within mitochondria. Highly specific labeling of mitochondria is also obtained in rat tissues, including adrenal gland, cerebellum, cerebral cortex, heart, kidney, liver, pituitary, pancreas, skeletal muscle, spleen, testes and thyroid. However, strong P32 (gClq-R) reactivity is also present in (i) zymogen granules, condensing vacuoles, endoplasmic reticulum, and on the cell surface of pancreatic acinar cells, (ii) on the cell surface of microvascular endothelial cells in pancreas and kidney, (iii) on the cell surface and in nuclei of splenic lymphocytes, and (iv) in the acrosome of developing spermatids in testes. Western immunoblots show that the polyclonal antibody to P32 (gC1q-R) used in this study reacts specifically with a 32-kDa protein in both purified pancreatic zymogen granules and in mitochondria, and no other proteins are reactive. These results provide evidence that P32 (gC1q-R) is a mitochondrial protein that also localizes outside mitochondria in certain cells and tissues under normal physiological conditions.
authors.affiliation: Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
authors.forename: B J
authors.initials: BJ
authors.lastname: Soltys
authors.forename: D
authors.initials: D
authors.lastname: Kang
authors.forename: R S
authors.initials: RS
authors.lastname: Gupta
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000166:cytology; D002051:Burkitt Lymphoma; D016466:CHO Cells; D002352:Carrier Proteins; D002417:Cattle; D006224:Cricetinae; D003594:Cytoplasmic Granules / Q000648:ultrastructure; D004730:Endothelium, Vascular / Q000648:ultrastructure; D005347:Fibroblasts / Q000166:cytology; D006367:HeLa Cells; D006801:Humans; D018960:Hyaluronan Receptors; D008297:Male; D008562:Membrane Glycoproteins; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron; D008928:Mitochondria / Q000737:chemistry / Q000648:ultrastructure*; D024101:Mitochondrial Proteins; D010179:Pancreas / Q000648:ultrastructure; D051381:Rats; D011951:Receptors, Complement / Q000032:analysis*; D014407:Tumor Cells, Cultured
chemical_list: C087299:C1QBP protein, human; C490195:C1qbp protein, rat; D002352:Carrier Proteins; D018960:Hyaluronan Receptors; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011951:Receptors, Complement; C032402:complement 1q receptor