Membrane and Secretory Proteins 
Mary-Jane H. Gething, Ph.D. — Investigator 
Dr. Gething is also Professor of Biochemistry at the University of Texas Southwestern Medical Center at 
Dallas. She received her bachelor's and Ph.D. degrees at the University of Melbourne. After holding re- 
search fellowships in Cambridge, England, with Brian Hartley and in London with Michael Waterfield, she 
joined the scientific staff of the Imperial Cancer Research Fund, London. After that she was a senior staff 
investigator at the Cold Spring Harbor Laboratory, New York, for three years before going to the University 
of Texas. 
INVESTIGATIONS in this laboratory focus on 
the molecular genetics of membrane and se- 
cretory proteins. Experiments involve three pro- 
teins: the hemagglutinin (HA) of influenza virus, 
which serves as a marker molecule for specific 
cell populations in transgenic mouse experi- 
ments; human tissue-type plasminogen activator 
(t-PA) , a serine protease produced in vascular en- 
dothelial cells and involved in thrombolysis (dis- 
solving blood clots); and BiP/GRP78, a protein 
of the endoplasmic reticulum (ER) that is in- 
volved in the initial mobilization of proteins that 
traverse the secretory pathway. 
Development of a Model for Autoimmune 
Type I Diabetes 
In type I diabetes the destruction of insulin- 
producing pancreatic /3 cells is thought to occur 
via an autoimmune mechanism — an immune re- 
sponse directed against the host. Surface mole- 
cules of the |S cells have been implicated as target 
antigens. We have used HA as a marker molecule 
to investigate the mechanism of immunological 
tolerance and to develop an animal model for the 
study of diabetes. 
In collaboration with Robert Hammer (HHMI, 
University of Texas Southwestern Medical Center 
at Dallas) , we have microinjected the HA gene — 
placed under the control of sequences from the 
rat insulin II gene — into fertilized mouse em- 
bryos to generate three lines of transgenic RIPHA 
mice in which the transgene is expressed only in 
the (8 cells of the pancreas. We have now bred 
large numbers of transgenic mice that are homo- 
zygous for the HA gene and for the major 
histocompatibility gene. 
From birth these transgenic animals have 
slightly raised blood glucose levels compared 
with those in control animals. Although histologi- 
cal analysis of the pancreata of young RIPHA mice 
reveals some disorganization of the normally or- 
dered architecture of the islets, these animals dis- 
play no physiological problems until approxi- 
mately 4-5 months of age. However, after this 
time up to 27 percent of the RIPHA mice develop 
frank diabetes mellitus as a consequence of lym- 
phocyte-mediated autoimmune destruction of 
the pancreatic ^ cells. Analyses of the sera of dia- 
betic animals often reveal the presence of anti- 
bodies directed against HA, as well as antibodies 
that recognize proteins of the /3 cells. The high 
blood glucose levels in the diabetic mice can be 
decreased to normal levels by administration of 
insulin. Therefore the development of hypergly- 
cemia in these transgenic mice has all the features 
that typify the pathogenesis of human type I dia- 
betes mellitus. These mice should provide a use- 
ful animal model for further studies of this 
disease. 
The development in RIPHA mice of immune 
responses against HA raises the question of why 
the protein, which is expressed on the /3 cells of 
the developing pancreas before thymic matura- 
tion, is not recognized as a self antigen. Addi- 
tional lines of transgenic mice have now been 
developed that express HA under the control of 
the mouse metallothionein promoter. These 
MTHA mice, which express high levels of HA in 
many tissues (including liver and kidney), will 
enable investigation of the immunological re- 
sponses to HA when the protein is expressed in 
major cell populations. Thus far, MTHA mice up 
to 10 months of age have displayed no signs of 
diabetes or any other autoimmune disease. 
Human Tissue-Type Plasminogen Activator 
Many normal and abnormal processes requir- 
ing extracellular proteolysis are thought to be 
mediated by plasminogen activators that cleave 
plasminogen to the active protease plasmin. Evi- 
dence points to t-PA as the physiological thrombo- 
lytic agent in the vascular system. 
The level of t-PA activity in the circulation is 
controlled by the interaction of the molecule 
with three other proteins. First, the affinity of the 
enzyme for its substrate plasminogen is increased 
several hundredfold by binding to fibrin. Second, 
t-PA is rapidly inactivated by the serpin, plasmin- 
ogen activator inhibitor- 1 (PAI- 1 ) . PAJ- 1 acts as a 
suicide substrate and forms a covalent bond with 
a serine residue in the active site of t-PA. Finally, 
the enzyme is efficiently cleared from the blood 
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