In malignant animal tisses, both the activity and regulatory properties of HMG-CoA reductase, the rate limiting enzyme in cholesterolgenesis, are markedly altered such that: (1) total enzyme activity is increased; (2) more enzyme exists in an active, unphosphorylated form; and (3) feedback responsiveness to plasma cholesterol is absent or diminished. These abnormalities are early events in malignant transformation and may be critical to development of the malignant state. Reductase activity is also integral in controlling progression of normal cells through the cell cycle. We hypothesize that the rapid and uncontrolled growth rate of malignant cells is due to abnormal control of reductase activity and that these abnormalities may precede development of the malignant phenotype. This hypothesis will be addressed by: (1) comparing the regulatory properties of normal and malignant leukocytes; (2) comparing the time, magnitude and duration of reductase elevation during the cell cycle, using normal and malignant cultured human leukocytes synchronized in G-1 phase of the cell cycle by centrifugal elutriation; (3) examining changes in these properties in malignant leukocytes in response to tsreatment with reductase inhibitors, antimitotic agents or antileukemic drugs; and (4) examining changes in reductase regulatory properties and cell cycle involvement as cultured promyelocytic leukemia cells are induced to differentiate and as leukemic patients experience remission or relapse. Our recently developed methods for measuring human leukocyte microsomal reductase activity, reductase protein concentrations (by an enzyme-linked immunosorbent assay), and enzyme phosphorylation state will permit us to address thse questions in ways not previously possible. These studies should aid in our understanding of the relationship between cellular cholesterol metabolism and malignancy and may be important in determining whether abnormal regulation of reductase activity precedes development of malignancy. (B)

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Unknown (R23)
Project #
1R23CA040495-01
Application #
3446786
Study Section
Physiological Chemistry Study Section (PC)
Project Start
1985-07-01
Project End
1988-06-30
Budget Start
1985-07-01
Budget End
1986-06-30
Support Year
1
Fiscal Year
1985
Total Cost
Indirect Cost
Name
University of Florida
Department
Type
Schools of Medicine
DUNS #
073130411
City
Gainesville
State
FL
Country
United States
Zip Code
32611
Harwood Jr, H J; Alvarez, I M; Noyes, W D et al. (1991) In vivo regulation of human leukocyte 3-hydroxy-3-methylglutaryl coenzyme A reductase: increased enzyme protein concentration and catalytic efficiency in human leukemia and lymphoma. J Lipid Res 32:1237-52
Harwood Jr, H J; Bridge, D M; Stacpoole, P W (1988) Erythrocyte contamination of leukocyte populations following density-gradient centrifugation results in artificially high levels of human leukocyte HMG-CoA reductase activity. Lipids 23:1154-8
Grant, M B; Russell, B; Harwood Jr, H J et al. (1987) Separation of the insulin-like growth factor-binding proteins in plasma and purification of the larger molecular weight species. J Clin Endocrinol Metab 64:1060-5
Stacpoole, P W; Bridge, D M; Alvarez, I M et al. (1987) In vivo regulation of human mononuclear leukocyte 3-hydroxy-3-methylglutaryl coenzyme A reductase. Decreased enzyme catalytic efficiency in familial hypercholesterolemia. J Clin Invest 80:1401-8
Harwood Jr, H J; Bridge, D M; Stacpoole, P W (1987) In vivo regulation of human mononuclear leukocyte 3-hydroxy-3-methylglutaryl coenzyme A reductase. Studies in normal subjects. J Clin Invest 79:1125-32
Harwood Jr, H J; Alvarez, I M; Greene, Y J et al. (1987) Development of a noncompetitive, solid phase, bridged biotin-avidin enzyme immunoassay for measurement of human leukocyte microsomal HMG-CoA reductase protein concentration. J Lipid Res 28:292-304
Harwood Jr, H J; Greene, Y J; Stacpoole, P W (1986) Inhibition of human leukocyte 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by ascorbic acid. An effect mediated by the free radical monodehydroascorbate. J Biol Chem 261:7127-35