tive roles of transcriptional and post-transcriptional 
regulation of the IR gene and how this regulation 
compares with other housekeeping genes. 
Reporter gene analysis using human IR promot- 
er-chloramphenicol acetyltransferase (hIR-CAT) fu- 
sion plasmids established regions responsible for 
promoter activity and verified the localization of the 
major IR gene transcriptional initiation sites. How- 
ever, transfection with hIR-CAT plasmids containing 
upstream regions resulted in increased utilization 
of the most 5' IR gene mRNA initiation sites in 
transfected relative to untransfected cells. Reporter 
gene analysis also established that a region of the 
IR promoter and first exon containing all of the 
transcriptional initiation sites is more active in 
HepG2 than CVl cells. Because the steady-state 
level of expression of the IR gene is much higher in 
HepG2 than CVl cells, the results of the reporter 
gene analysis may reflect tissue-specific differences 
in IR gene transcription. Such tissue-specific tran- 
scriptional regulation would be a novel finding in a 
housekeeping promoter. Unlike the reporter gene 
analyses, nuclear run-on studies of IR mRNA give 
similar results in HepG2 and CVl cells, suggesting 
that IR gene expression may not be regulated in a 
tissue-specific manner at the level of RNA initiation. 
The different conclusions drawn from reporter 
gene and nuclear run-on analyses could be ex- 
plained if downstream GC-rich regions within the 
IR first exon and intron, not included in the re- 
porter gene constructions, contribute significantly 
to the basal activity of the IR promoter, thus elimi- 
nating the tissue-specific transcriptional effect me- 
diated by upstream sequences. 
In addition, it appears that cells from a patient 
with severe insulin resistance and markedly re- 
duced levels of IR mRNA give normal results in nu- 
clear run-on studies of the IR gene. The IR gene 
mutation in this patient may cause a post-transcrip- 
tional effect on IR gene stability. 
III. Antireceptor Monoclonal Antibodies That Bind 
to the Ligand-binding Domain. 
Dr. Taub's laboratory previously noted that a lin- 
ear sequence, arginine-tyrosine-aspartic acid, with- 
in the hypervariable region of an antifibrinogen re- 
ceptor monoclonal antibody, R\C1, appeared to 
mimic the arginine-glycine-aspartic acid sequence 
within fibrinogen that recognizes the fibrinogen re- 
ceptor. These studies are being extended by isolat- 
ing anti-idiotypic antibodies directed against the 
R\C1 monoclonal antibody and peptides within the 
PACl variable regions to determine if these anti-idi- 
otypic antibodies have linear amino acid sequences 
similar to the fibrinogen receptor. In addition, the 
PACl monoclonal antibody variable regions are 
being expressed in a prokaryotic system to allow 
further genetic manipulation of the sequences im- 
portant in fibrinogen receptor binding. 
Further studies are under way to determine if 
this immunologic approach to receptor-ligand in- 
teractions may be generally applied to other anti- 
receptor monoclonal antibodies. Dr. Taub and her 
colleagues are presently analyzing anti-idiotypic an- 
tibodies isolated by Dr. Bernard Erlanger (Colum- 
bia University), directed against the thyroid-stimu- 
lating hormone (TSH) receptor, that appear to bind 
to the TSH-binding site. The analyses of these anti- 
TSH receptor monoclonal antibodies could prove 
particularly interesting, because in Graves' disease, 
autoantibodies to the TSH receptor may also bind 
to the TSH-binding site on the TSH receptor. The 
immunoglobulin variable regions from anti-TSH re- 
ceptor anti-idiotypic antibodies are presently being 
sequenced and the sequences analyzed for similar- 
ity with TSH. 
Dr. Taub is also Assistant Professor of Human Ge- 
netics at the University of Pennsylvania School of 
Medicine. 
PUBLICATIONS 
Articles 
Banskota, N.K., Taub, R., Zellner, K., Olsen, R, and King, G.L. 1989. Characterization of induction of proto- 
oncogene c-myc and cellular growth in human vascular smooth muscle cells by insulin and IGF-1. Diabe- 
tes 58:125-129. 
Cox, N.J., Spielman, R.S., Kahn, R.C., MuUer-Wieland, D., Kriauciunas, K.M., and Taub, R. 1989. Four RFLPs of 
the human insuhn receptor gene: Pstl, Kpnl, Rsal (2 RFLPs). Nucleic Acids Res 17:820. 
Continued 
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