This work is focused on the clinical problem of myocardial hypertrophy, specifically the molecular mechanisms which regulate this process. A new model system was developed to study hypertrophy, employing neonatal heart myocytes in serum-free culture. The novel observation was made that stimulation of the alpha 1-adrenergic receptor on these cells by the catecholamine norepinephrine induces cell enlargement or hypertrophy, without DNA synthesis. The alpha 1-adrenergic receptor is the first receptor shown to regulate cardiac myocyte hypertrophy. Recent work has shown that the alpha 1 receptor regulates mRNA expression during hypertrophy. In particular, alpha 1 stimulation induces two contractile protein iso-mRNAs characteristic of early cardiac development and pressure-load hypertrophy in vivo, skeletal alpha-actin iso-mRNA and B-myosin heavy chain iso-mRNA. This alpha 1 receptor effect is selective and is mediated at the level of iso-gene transcription. Thus, the critical question is the mechanism for induction of transcription by the alpha 1 receptor. The present experiments will test the hypothesis that the skeletal alpha- actin iso-gene and the B-myosin heavy chain iso-gene contain one or more alpha 1 response elements, i.e., DNA sequences required specifically for transcription of these genes in response to alpha 1-adrenergic stimulation. Two complementary experimental approaches for functional identification alpha 1 response elements are proposed: (1) transfection of hybrid genes in a transient assay system; and (2) DNase I hypersensitivity mapping. The necessary cloned genes are available to begin these experiments and preliminary studies provide evidence that the work is feasible. The long-range goal is to define the intracellular pathway from the alpha 1 receptor at the cell surface to gene transcription. The overall hypothesis is that receptor stimulation activates a pre-existing protein or proteins that binds to the alpha 1 response element in a transcriptional complex with RNA polymerase II. Identification of an alpha 1 response element or elements in the present work will provide the foundation for subsequent identification of the protein or proteins.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL042150-05
Application #
2220318
Study Section
Cardiovascular and Pulmonary Research A Study Section (CVA)
Project Start
1989-07-01
Project End
1995-06-30
Budget Start
1993-07-01
Budget End
1995-06-30
Support Year
5
Fiscal Year
1993
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
073133571
City
San Francisco
State
CA
Country
United States
Zip Code
94143