MEMBRANE LIPIDS AND THE REGULATION OF CELLULAR METABOLISM AND FUNCTION 
John A. Glomset, M.D., Investigator 
Two major areas of investigation are being pur- 
sued in Dr. Glomset 's laboratory: 1) the structure, 
metabolism, and function of membrane lipids and 
2) the structure and function of membrane pro- 
teins that are modified by isoprene groups. 
I. Structure, Metabolism, and Function of Membrane 
Lipids. 
In collaboration with Dr. Andreas Habenicht 
(University of Heidelberg), mechanisms that control 
the formation of prostaglandins and other 
eicosanoids are being studied in replicating fibro- 
blasts and differentiating macrophages. Early exper- 
iments with replicating Swiss 3T3 cells in culture 
showed that these cells produce prostaglandin 
in two phases during the cell cycle. A transient, 
early phase occurs almost immediately in response 
to the addition of platelet-derived growth factor 
(PDGF), whereas a second phase occurs after the 
cells have traversed the cell cycle for 2-6 h. The 
first phase resembles that seen in many other pros- 
taglandin-response systems, in that the arachidonic 
acid that is required for prostaglandin production is 
released from membrane phospholipids by one or 
more phospholipases. In contrast, the second 
phase of prostaglandin formation only occurs in 
the presence of exogenous unesterified arachidonic 
acid or low-density lipoproteins (LDL) and is associ- 
ated with the PDGF-dependent upregulation of at 
least two major enzymes of prostaglandin synthesis, 
prostaglandin H synthase and prostacyclin syn- 
thase. 
Experiments conducted during the past year pro- 
vided important new information about the mecha- 
nism of the LDL effect. The effect is clearly medi- 
ated by the LDL receptor, which also is upregulated 
in response to PDGF. Thus only low concentrations 
of LDL are required, antibodies to the LDL receptor 
block the effect, and the effect is not seen in fibro- 
blasts from patients with familial hyper- 
cholesterolemia. Uptake and degradation of LDL 
seem to be required, because the effect of LDL is 
blocked by chloroquine, an inhibitor of lysosomal 
hydrolases. Furthermore, experiments with recon- 
stituted LDL containing labeled, esterified arachi- 
donic acid have shown that the effect of LDL de- 
pends on the delivery of arachidonic acid for 
prostaglandin production. This is a new role for the 
LDL receptor that might be of considerable regula- 
tory importance. Experiments are under way to ex- 
plore its significance for cell cycle progression. 
II. Isoprene-containing Proteins. 
Experiments in Dr. Glomset's laboratory re- 
ported last year, demonstrated that lamin B, a 
structural protein associated with the nuclear enve- 
lope, is modified by an isoprene group. Recent ex- 
periments, in collaboration with Dr. Michael Gelb 
(University of Washington), have provided evidence 
that a cysteine residue at the carboxyl end of lamin 
B contains a thioether-linked farnesyl group. This is 
the first direct evidence of the farnesylation of ani- 
mal cell proteins. 
Dr. Glomset is also Professor of Medicine and of 
Biochemistry at the University of Washington 
School of Medicine and Core Staff Member of the 
Regional Primate Research Center. 
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