Project: Research project

Project Details


We will examine thyroid hormone effects on cell growth in cultured
GC cells, a thyroid hormone-sensitive cell line that secretes GH.
We have synchronized these cells in early Gl and demonstrated that
T3 induces growth during the first 4-6h of the Gl period. Growth
induction by T3 has characteristics suggesting mediation by the
nuclear T3 receptor and demonstrates a requirement for protein
synthesis. We now propose to identify the specific proteins and
phosphoproteins that are regulated by T3 at the Gl commitment point
by pulse-labelling and 2-dimensional gel electrophoresis. The
regulation by T3 of specific Gl mRNAs will be determined by
differential hybridization of a cDNA library in lambda-gtlO phage
vector. The time course and dose-dependence of these Gl responses
will be assessed. Since GC cell growth can also be regulated by
GC cell conditioned medium, calf serum growth factor,
hydrocortisone, EGF and defined medium, we will determine whether
these regulators result in biochemical changes that are similar to
those induced by T3.

We have previously shown that T3 nuclear receptor concentration is
augmented in S phase of the cell cycle and is localized to the
nuclear matrix, a DNA and salt resistant nuclear fraction that is
associated with new DNA synthesis and transcription complexes. We
now propose to examine the physico-chemical characteristics of
nascent T3 receptor molecules in conjunction with nascent DNA in
the S phase of the cell cycle. We propose to clarify the
relationship between nuclear T3 receptor and nuclear matrix by
determining the role of disulfide bonds and metal ion complexes in
this interaction. These studies should elucidate the nature of the
physico-chemical association of T3 receptor to DNA and chromatin.

We have reported that the rate of GH mRNA synthesis is decreased
in S phase of the cell cycle, an interval when nuclear receptor
concentration is augmented. To explain the dissociation between
T3 receptor concentration and mRNA synthesis, we now propose to
measure the transcription rate of GH in GC cell populations that
are synchronized in Gl and S phase. Lastly, we will determine
whether these synchronized GC cell populations contain cell cycle-
specific trans-acting factors which may mediate the cell cycle-
specific regulation of GH transcription.
Effective start/end date12/31/8911/30/93


  • Medicine(all)
  • Cell Biology