On leave of absence in 1983 through 1988,
he served for five years as worldwide research director for the Ludwig
Institute for Cancer Research, based in Zürich, and one year as a
Fogarty Scholar at the National Institutes of Health. After retirement
from Chicago in 1990, he was Scholar-in-Residence at Cornell Medical
College, Alexander von Humboldt visiting professor at the University of
Hamburg, and Nobel visiting professor at the Karolinska Institute in
Stockholm, before his present appointment at UC. Dr. Jensen is
collaborating with Sohaib Khan, PhD, professor of cell biology, to
elaborate the mechanism of estrogen actions.
Dr. Jensen's studies on estrogenic
hormones completely revolutionized earlier concepts of the mechanism of
steroid hormone action. During the 1950s, attention had been focused on
the influence of estrogens on enzymes involved in biosynthesis. He took
a different approach: not what does the hormone do to the tissue, but
what happens to the hormone itself as it stimulates growth of the
female reproductive tissues. To detect products resulting from
administration of physiological doses of estrogen, he needed labeled
hormone of much higher specific radioactivity than had ever been known
before. Dr. Jensen devised a procedure for labeling estradiol with pure
tritium, making possible the detection of one-trillionth of a gram.
With this he identified an intracellular receptor protein in the rat
uterus with which the hormone combines to bind tightly in the cell
nucleus and stimulate RNA synthesis without itself undergoing metabolic
change. This sowed the seed for a new area of research; Dr. Jensen is
the father of the now very important "Nuclear Receptor" field. Dr.
Jensen's landmark discoveries have had important clinical applications.
He showed that estrogen receptor analysis of tumor tissue can identify
the one-third of breast cancer patients who will benefit from hormonal
therapy, thus allowing the others to be placed directly on chemotherapy
without first undergoing treatment that will not help them. Estrogen
receptor analysis of breast cancers for therapy selection is now
standard clinical practice. His success in preparing the first
antibodies to any steroid hormone receptor provided a widely used
immunoassay for this purpose.