growth factors, it was determined in this laboratory 
that protein phosphatases are also subject to regu- 
lation. Incubation of Swiss 3T3-D1 cells with physi- 
ological concentrations of insulin resulted in a 
rapid and transient activation of protein phospha- 
tase activity. Activation reached a maximum level 
(140% of control value) within 5 min of addition 
and returned to control levels within 20 min. This 
activity could be completely inhibited by addition 
of the heat-stable protein inhibitor 2, which sug- 
gests the presence of an activated type-1 phospha- 
tase. Similar effects on phosphatase activity were 
seen when epidermal grovvT:h factor and platelet- 
derived growth factor were tested. 
IV Protein Tyrosine Phosphatases and Signal 
Transduction. 
With the finding that the receptors for a number 
of growth factors are protein tyrosine kinases and 
that a number of oncogenes encode similar en- 
zymes, attention has been focused on tyrosine 
phosphorylation-dephosphorylation as a mecha- 
nism involved in intracellular signaling. Until re- 
cently almost all of the work in this area involved 
the tyrosine kinases, but during this past year some 
of the emphasis has shifted to studies of the pro- 
tein tyrosine phosphatases (PTPases). 
In collaboration with Dr. E. H. Fischer's group, 
this laboratory has been studying several PTPases, 
one of which, PTPase IB, was obtained from 
human placenta in the pure form. It was found to 
consist of a single chain of 321 residues with an 7V- 
acetylated amino-terminal methionine and an un- 
usually proline-rich carboxyl-terminal region. The 
PUBLICATIONS 
enzyme is related structurally to the two cytoplas- 
mic domains of both the leukocyte common anti- 
gen CD45 and LAR, a CD45-like molecule with an 
external segment that resembles a neural cell adhe- 
sion molecule. A low-molecular- weight protein en- 
coded by a cDNA clone from T cells (see below) 
also shows extensive sequence similarities. Homol- 
ogous domains common to this diverse family of 
PTPases were defined. 
A human peripheral T cell cDNA library was 
screened with two labeled synthetic oligonucleo- 
tides encoding regions of the human placental 
PTPase IB. One positive clone was isolated, and the 
nucleotide sequence was determined. It contained 
1,305 base pairs of open reading frame followed by 
a TAA stop codon and 978 base pairs of 3' se- 
quence. An initiator methionine residue was pre- 
dicted at position 61, which would result in a pro- 
tein of 415 amino acid residues (M^ 48,400). This 
was supported by the synthesis of an 48,000 
protein in an in vitro reticulocyte lysate translation 
system using RNA transcribed from the cloned 
cDNA and T7 RNA polymerase. The deduced amino 
acid sequence was compared with other known 
proteins, revealing 65% identity to the low-molecu- 
lar-weight PTPase IB isolated from placenta. In 
view of the high degree of similarity, the T cell 
cDNA likely encodes a newly discovered protein ty- 
rosine phosphatase, thus expanding this family of 
genes. Experiments have been undertaken to over- 
express this enzyme in transformed cells. 
Dr. Krebs is also Professor of Pharmacology and 
of Biochemistry at the University of Washington 
School of Medicine. 
Books and Chapters of Books 
Blumenthal, D.K., and Krebs, E.G. 1988. Calmodulin-binding domains on target proteins. In Molecular As- 
pects of Cellular Regulation, Calmodulin (Cohen, P., and Klee, C, Eds.). Amsterdam: Elsevier, vol 5, pp 
341-356. 
Articles 
Blumenthal, D.K., Charbonneau, H., Edelman, A.M., Hinds, T.R., Rosenberg, G.B., Storm, D.R., Vincenzi, F.F., 
Beavo, J.A., and Krebs, E.G. 1988. Synthetic peptides based on the calmoduUn-binding domain of myosin 
light chain kinase inhibit activation of other calmodulin-dependent enzymes. Biochem Biophys Res Com- 
mun 156:860-865. 
Chan, CP , McNall, S.J., Krebs, E.G. , and Fischer, E.H. 1988. Stimulation of protein phosphatase activity by in- 
sulin and growth factors in 3T3 cells. Proc Natl Acad Sci USA 85:6257-6261. 
Continued 
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