Despite much indirect evidence that protein ki- 
nase C is a major factor in the control of PC hydroly- 
sis by many hormones and growth factors, direct ef- 
fects of the kinase on PC breakdown have not been 
demonstrated. Plasma membranes from CCL39 fi- 
broblasts were used to stimulate PC phospholipase 
D activity by the dose-dependent addition of puri- 
fied protein kinase C and phorbol ester. Addition of 
either alone was without effect. Surprisingly, addi- 
tion of ATP was not required, and the inclusion of an 
ATPase did not diminish the effect. Furthermore, ac- 
tivation of phospholipase D could be demonstrated 
with protein kinase C plus phorbol ester in the total 
absence of histone phosphorylation or autophos- 
phorylation of the kinase. These results establish 
that protein kinase C can regulate phospholipase D, 
but phosphorylation is not involved: i.e., the regula- 
tion involves a protein-protein interaction. The spe- 
cific protein kinase C isozymes and the specific pro- 
tein domains involved are being studied. 
Dr. Exton is also Professor of Molecular Physiol- 
ogy and Biophysics and of Pharmacology at Van- 
derbilt University School of Medicine. 
Books and Chapters of Books 
Bocckino, S.B., and Exton, J.H. 1992. Phosphati- 
dylcholine metabolism in signal transduction. In 
Cellular and Molecular Mechanisms of Inflam- 
mation (Cochrane, C, and Gimbrone, M., Jr., 
Eds.). San Diego: Academic, vol 3, pp 89-1 14. 
Exton, J.H. 1991. Mechanisms of action of cal- 
cium-mobilizing hormones. In Recent Advances 
in Biochemistry (Byun, S., Lee, S.Y., and Yang, 
C.H., Eds.). Seoul: Biochemical Society of the Re- 
public of Korea, pp 321-332. 
Lynch, C.J., and Exton, J.H. 1992. Alterations in 
G-protein-mediated cell signalling in diabetes 
mellitus. In G-Proteins Signal Transduction and 
Disease (Milligan, G., and Wakelam, M., Eds.). 
London: Academic, pp 87-108. 
Articles 
Berstein, G., Blank, J.L., Smrcka, A.V., Higashi- 
jima, T., Sternweis, P.C., Exton, J.H., and Ross, 
E.M. 1992. Reconstitution of agonist-stimulated 
phosphatidylinositol 4,5-bisphosphate hydrolysis 
using purified ml muscarinic receptor, Gqyn, and 
phospholipase C-|8l. / Biol Chem 267:8081- 
8088. 
Blank, J.L. , Ross, A.H. , and Exton, J.H. 1991 Puri 
fication and characterization of two G-proteins 
that activate the |8l isozyme of phosphoinositide- 
specific phospholipase C. Identification as 
members of the G^ class. / Biol Chem 266: 
18206-18216. 
Bocckino, S.B., Wilson, P.B., and Exton, J.H. 
1991. Phosphatidate-dependent protein phos- 
phorylation. Proc Natl Acad Sci USA 88:6210- 
6213. 
Conricode, K.M., Brewer, K.A., and Exton, J.H. 
1992. Activation of phospholipase D by protein 
kinase C. Evidence for a phosphorylation-indepen- 
dent mechanism. /B/o/ Chem 267:7199-7202. 
Exton, J.H., Taylor, S.J., Augert, G., and Boc- 
ckino, S.B. 1991. Cell signalling through phos- 
pholipid breakdown. Mol Cell Biochem 104:81- 
86. 
Exton, J.H., Taylor, S.J., Blank, J.L., and Boc- 
ckino, S.B. 1992. Regulation of phosphoinosi- 
tide and phosphatidylcholine phospholipases by 
G-proteins. Ciba Found Symp 164:36-49. 
Siddiqui, R.A., and Exton, J.H. 1992. Phospho- 
lipid base exchange activity in rat liver plasma 
membranes. Evidence for regulation by G-protein 
and P2y-purinergic receptor. / Biol Chem 267: 
5755-5761. 
Stewart, S.J., Cunningham, G.R., Strupp, J. A., 
House, F.S., Kelley, L.L., Henderson, G.S., Ex- 
ton, J.H. , and Bocckino, S.B. 1991 . Activation of 
phospholipase D: a signaling system set in motion 
by perturbation of the T lymphocyte antigen re- 
ceptor/CD3 complex. Cell Regul 2:841-850. 
Taylor, S.J., and Exton, J.H. 1991- Two a subunits 
of the Gq class of G proteins stimulate phosphoin- 
ositide phospholipase C-/31 activity. FEBS Lett 
286:214-216. 
CELL BIOLOGY AND REGULATION 53 
