MOLECULAR BIOLOGY OF HORMONE REGULATED CYTOLYSIS

The observed physiological response to hormone treatment is the
coordinate regulation of tissue-specific gene networks. The
effects of steroid hormones are mediated by intracellular
receptor proteins. Hormone receptor complexes are tightly
associated with the nucleus and have high affinities for specific
DNA sequences found within and near hormone-responsive genes.
Glucocorticoid receptors (GR) have been extensively
characterized at the biochemical and genetic level; this analysis
has been facilitated by the recent isolation of GR coding
sequences. The site of GR action on the DNA has also been
examined in detail; the GR binds specifically in vitro to the same
sequence which acts in vivo as a hormone-inducible
transcriptional enhancer. One example of a cell specific hormone
response is the GR-dependent induction of cytolysis in two murine
thymoma cell lines (WEHI7) and S49). The molecular basis for the
observed cell death in these cells is not known, but is most likely
regulated at the level of transcription by the GR. Since
glucocorticoids are useful in the treatment of several human
lymphatic cancers, it has been suggested that the hormoneinduced
cell death of WEHI7 and S49 cells may be a good model system for
the study of clinical responses to steroid therapy, such as tumor
regression and cytolysis of leukemic cells. We propose to use several molecular biological approaches to
identify the mechanism of hormone-regulated cytolysis. First, we
will determine what GR activities are required for cytolysis by
isolating and characterizing GR coding sequences (cDNA and
genomic) from a unique class of steroid resistant mutants which
express a form of the GR that binds hormone and DNA, but is
apparently defective in its ability to modulate transcription.
Second, we will isolate genes required for lysis using the
techniques of subtraction cDNA cloning and retrovirus-mediated
transposon tagging. The long term goal of this study is to
delineate tissue-specific glucocorticoid gene networks using
molecular genetics and to understand how GR-dependent gene
expression is coordinately and developmentally regulated.