title: A 54-kDa protein related to ras-guanine nucleotide release factor expressed in the rat exocrine pancreas.
abstract: The polymerase chain reaction was used to amplify a cDNA encoding the catalytic region of ras-guanine nucleotide release factor (ras-GRF1) from mouse embryonic stem cell mRNA. Antibodies directed against this protein were prepared and affinity purified. Western immunoblotting of rat tissue lysates revealed a 140-kDa protein in brain as expected but, in addition, a strongly immunoreactive 54-kDa protein, p54, was identified in pancreas. Expression of ras-GRF1 in pancreas was confirmed at the RNA level by reverse-transcriptase-coupled polymerase chain reaction analysis; p54 may therefore correspond to a form of ras-GRF1 or a closely related protein. The cellular and subcellular localization of p54 was investigated by enzyme-linked immunocytochemistry and immunogold electron microscopy. In the pancreas, p54 was expressed primarily in acinar cells, where it was localized along the basolateral and apicolateral plasma membranes. Indirect immunofluorescence microscopy of cultured acini further indicated that the plasma membrane localization of p54 was dependent on the maintenance of the acinar histotype and organized acinar structure. When primary acinar cells were permitted to dissipate into monolayer cultures devoid of zymogen granules, ras-GRF1 staining became cytosolic. Our results suggest that ras-GRF1 is involved in the structure and function of the pancreas.
authors.affiliation: Charles H. Best Institute, Banting and Best Department of Medical Research, and Department of Molecular and Medical Genetics, University of Toronto, 112 College Street, Toronto, Ontario, Canada M5G 1L6.
authors.forename: P S
authors.initials: PS
authors.lastname: Tung
authors.forename: N P
authors.initials: NP
authors.lastname: Fam
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.forename: M F
authors.initials: MF
authors.lastname: Moran
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000818:Animals; D000918:Antibody Specificity; D001923:Brain Chemistry / Q000502:physiology; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000648:ultrastructure; D004268:DNA-Binding Proteins; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000648:ultrastructure; D005260:Female; D015870:Gene Expression / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors; D051379:Mice; D008854:Microscopy, Electron; D010179:Pancreas / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics* / Q000276:immunology; D011401:Promoter Regions, Genetic / Q000502:physiology; D011506:Proteins / Q000032:analysis / Q000235:genetics* / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins / Q000032:analysis / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; C091848:GRF1 protein, Zea mays; D020662:Guanine Nucleotide Exchange Factors; D010940:Plant Proteins; D011506:Proteins; D012333:RNA, Messenger; D020663:ras Guanine Nucleotide Exchange Factors; D018631:ras Proteins