ABSTRACT
1. A high expression of angiotensin II receptors and of angiotensin-converting enzyme (ACE) activity was detected in confluent NIH 3T3 fibroblasts. 2. Characterization with selective ligands, dithiothreitol, and GTP gamma S, indicated that only the AT2 subtype was expressed. 3. AT2 receptors and ACE expression were strictly dependent on the cell density and growth phase of the cells, with AT2 receptors being expressed earlier than ACE. In contrast, high expression of AT2 receptors irrespective of their growth state was observed in NIH 3T3 cells lacking contact inhibition upon neoplastic transformation with ras. 4. Our results imply a possible relation of AT2 receptors to cell growth and cell-cell contact.
Subject(s)
Receptors, Angiotensin/metabolism , Transformation, Genetic , 3T3 Cells/chemistry , 3T3 Cells/cytology , 3T3 Cells/enzymology , Adenosine Triphosphate/analogs & derivatives , Adenosine Triphosphate/pharmacology , Affinity Labels/pharmacology , Angiotensin II/analogs & derivatives , Angiotensin II/metabolism , Angiotensin II/pharmacology , Animals , Binding, Competitive/drug effects , Binding, Competitive/physiology , Cell Communication/physiology , Cell Division/genetics , Guanosine 5'-O-(3-Thiotriphosphate)/pharmacology , Guanosine Triphosphate/pharmacology , Iodine Radioisotopes , Mice , Peptidyl-Dipeptidase A/metabolism , Receptor, Angiotensin, Type 2ABSTRACT
In this study, we have characterized the 5' region of the human c-fgr proto-oncogene and identified the major myelomonocytic c-fgr promoter. Seven distinct 5' untranslated exons were identified and localized to a region extending 13 kb upstream from the first coding exon. Two major promoters were identified, one utilized exclusively in Epstein-Barr virus (EBV)-infected B-lymphocyte cell lines, and the other functional only in myelomonocytic cells. Differential promoter utilization and alternative splicing of the 5' untranslated exons give rise to at least six distinct c-fgr mRNA species that differ only in their 5' untranslated regions. Two major mRNAs were identified, c-fgr A and c-fgr 4; these two mRNAs were detected exclusively in EBV-infected B-lymphocyte cell lines and myelomonocytic cells respectively. We have previously demonstrated that c-fgr is transcriptionally activated in U937 cells treated with either 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or cycloheximide (CHX). We now show that a DNA fragment extending from -772 to +97 (with respect to the transcription initiation site upstream from exon M4) is responsive to TPA but not CHX treatment in U937 cells. These results suggest that TPA and CHX induce c-fgr mRNA accumulation by different mechanisms.
