Molecular Neuroimmunology 
Donald G. Payan, M.D. — Assistant Investigator 
Dr. Payan is also Associate Professor of Medicine and of Microbiology and Immunology at the University 
of California, San Francisco. He received his secondary education in Mexico and Switzerland and his B.S. 
degree in physics and mathematics from Stanford University. He went on to do graduate work in physics 
at the Massachusetts Institute of Technology and then returned to Stanford Medical School, where he re- 
ceived his M.D. degree. His medical residency at Massachusetts General Hospital, Boston, was followed by 
fellowships in infectious diseases at MGH and in allergy-immunology at Brigham and Women 's Hospital. 
MY laboratory is currently studying the inter- 
actions at the molecular level between the 
nervous and immune systems. These analyses are 
focused on the roles of certain receptors in cellu- 
lar differentiation and signal transduction and, 
more recently, on the organization of other 
unique cell surface components. Projects that are 
under wacy involve the expression of tachykinin 
receptors in cloned lymphocyte, epithelial, and 
neuronal cell lines and an analysis of their signal- 
ing pathways. In addition, we are studying the 
molecular biology of synaptogenesis, in particu- 
lar the function of the molecule agrin. 
With Richard Scheller (HHMI) and Fabio Rupp 
at Stanford University, I have worked on the clon- 
ing and structural analysis of the agrin molecule 
from the rat. Agrin belongs to a family of extracel- 
lular synaptic organizing molecules that have 
been shown to cause the aggregation of acetyl- 
choline receptors and acetylcholinesterase on 
the surface of regenerating and developing mus- 
cle fibers. A cDNA library constructed from 
poly (A) ^ RNA of embryonic rat spinal cord was 
screened, and a number of inserts were isolated 
that predicted amino acid sequences similar to 
those of agrin identified in the Torpedo electric 
organ. 
A number of these clones have now been se- 
quenced. We have constructed fusion proteins in 
order to raise specific antibodies, and we are 
studying the expression of the message for agrin 
in various tissues during the development of the 
rat. The deduced sequence contains several epi- 
dermal growth factor (EGF)-like domains and re- 
gions similar to the trypsin inhibitor enzyme. 
Moreover, Northern blot analysis reveals a mes- 
sage of about 8.2 kb in embryonic brain and spi- 
nal cord, which in the adult decreases about 10- 
fold and is only detectable in the cord. Current 
efforts are focused on expressing agrin in a num- 
ber of cell lines and studying its receptor-cluster- 
ing activity. In the future we will analyze its func- 
tionally active domains, possible binding sites, 
and cellular distribution in embryonic and adult 
rat tissues. 
With information derived from the cloning of 
the rat substance P (SP) receptor (SPR) , my labo- 
ratory is studying the expression and the signal- 
ing properties of the SPR in a number of cell 
lines. We have demonstrated that the SPR signals 
simultaneously by both the cAMP and IP3 (inosi- 
tol 1 ,4,5,-trisphosphate) pathways. 
With J. Sudduth-Klinger and C. Christian, I 
have transfected the SPR cDNA into Jurkat lym- 
phocytes and PCI 2 cells and established stable 
clones that express functional SPR. The initial 
characterization of the lines has been carried out. 
Jurkat-SPR cells will be studied to see if, when 
stimulated by SP, they alter the expression/pro- 
duction of specific cytokines or their receptors. 
Moreover, the coordinate regulation of CDjo (the 
cell surface neutral endopeptidase that deacti- 
vates SP) in Jurkat-SPR will be examined. We will 
study whether CDjo activation or inactivation by 
thiorphan (a neutral endopeptidase inhibitor) 
changes SP responses. In addition, we will also 
study whether CD 10 coprecipitates with the SPR. 
Preliminary immunohistochemical studies from 
rat lung and gut suggest that the SPR and CD 10 are 
colocalized. These experiments will for the first 
time allow us to elucidate the effects of SP on 
immune responses at a unicellular level in a well- 
defined system. 
I will study with Mark Gilben how the SPR in- 
fluences PC 1 2 cells before and after differentia- 
tion with nerve growth factor (NGF) . Functional 
studies are under way to examine whether SPR 
expression alters growth characteristics and mor- 
phology of the cells. Experiments from other lab- 
oratories done with primary cultures have shown 
that '^'l-SP binding is located in the growth 
cones, suggesting the receptor may play a role in 
certain aspects of neuronal development. 
349 
