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 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 received 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 continues to study the interac- 
tions between the nervous and immune sys- 
tems at the molecular level. Ongoing work is fo- 
cusing on the signal transduction pathways that 
are activated in cells into which we have trans- 
fected a number of neuropeptide receptors, in 
particular the tachykinin receptor for substance 
P. An additional effort is directed at understand- 
ing the biochemical properties of agrin, the nico- 
tinic acetylcholine receptor-clustering mole- 
cule, which was cloned and sequenced during 
sabbatical studies with Richard Scheller (HHMI, 
Stanford University) . 
The two main projects currently under way are 
the analysis of the signal transduction capabilities 
of the substance P receptor (SPR) and accessory 
molecules that mediate that signaling, and an 
analysis of agrin's protease inhibitor domains and 
their potential function in modulating neuronal 
plasticity in the developing brain. With Julie 
Sudduth-Klinger, Christine Christian, and Mark 
Gilbert, we have transfected SPR cDNA into a 
number of different immune cells, in particular 
Jurkat and Reh, in order to study the effects of this 
receptor's expression on the cells' immunologic 
properties. We can get approximately 100,000 
functional receptors per cell and can demon- 
strate a very brisk mobilization of intracellular 
calcium and inositol phosphate (IP3) metabo- 
lites following stimulation with substance P. 
Of great interest are many differences we have 
observed in comparing the Jurkat SPR with the 
Jurkat muscarinic receptor. Activation of the mus- 
carinic receptor results in desensitization of sub- 
sequent T cell receptor activation with an anti-T 
cell receptor antibody; conversely, activation of 
the T cell receptor does not result in desensitiza- 
tion of the transfected muscarinic receptor. In 
contrast, we find that activation of Jurkat SPRs by 
substance P does not desensitize subsequent T 
cell activation, but activation of the T cell recep- 
tor does result in desensitization of SPR. We are 
currently investigating whether some heterolo- 
gous desensitization mechanism is taking place 
and whether a particular kinase is involved. 
In collaboration with Phyllis Gardner at Stan- 
ford University, we have also been able to demon- 
strate, using patch-clamp techniques, that activa- 
tion of the SPR in these transfected lymphocytes 
results in the opening of a chloride channel. In 
addition, these changes can be nullified by in- 
jecting the cells with a calcium/calmodulin ki- 
nase inhibitor peptide. 
Our early observations that stimulation of these 
cell lines by substance P resulted in both IP3 and 
cyclic AMP activation have now been extended. 
Looking at the cells' respective nuclear regula- 
tory elements, we have demonstrated that sub- 
stance P stimulation results in increased expres- 
sion of the AP-1- and the cAMP-responsive 
elements in these cells. Furthermore, using West- 
ern and Northern blotting techniques, we have 
also been able to demonstrate that the proto- 
oncogenes /os and^wn are also up-regulated fol- 
lowing substance P stimulation. Consequently, 
signal transduction analysis suggests that a dual 
activation signal pathway may be activated when 
the SPR is expressed in lymphoid cells. 
We have studied the functional consequences 
of stimulating these cells with the peptide sub- 
stance P by examining the expression of a num- 
ber of cell surface antigens and their modulation 
on Jurkat SPRs. We find that in Jurkat SPR-positive 
cells, substance P stimulation results in a down- 
regulation of the LFA- 1 (integrin) surface antigen 
and an up-regulation of the CD2 surface antigen. 
In addition, when combined with the mitogen 
phytohemagglutinin, substance P stimulation re- 
sults in an increased expression of the interleu- 
kin-2 receptor. We continue to examine these re- 
sults in order to delineate further how tachykinin 
peptides may modulate immune responses. 
Joseph Fisher and Sandra Biroc have now begun 
an extensive in situ hybridization study of the 
expression of agrin and alternate agrin transcripts 
in the developing rat. Preliminary results suggest 
that agrin is extensively expressed in unique sites 
within the developing brain. Moreover, Dr. 
Fisher has now expressed full-length recombi- 
nant agrin in a number of cell types and is examin- 
ing the molecule's biochemical properties. In 
particular, the amino terminus of the molecule 
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