Project Details


The long term goal of this proposal is to understand molecular mechanisms
that regulate microfilament reorganization during mitosis, as well as
during oncogenic transformation of cultured cells. We will focus our
studies on the biological significance of the mitosis-specific
phosphorylation of caldesmon. We have demonstrated, for the first time,
that nonmuscle caldesmon, a protein of relative molecular mass Mr = 83,000
which binds to actin and calmodulin, is disassociated from microfilaments
during mitosis, apparently as a consequence of phosphorylation. We believe
that this process may contribute to the changes of shape and structure seen
in cells undergoing mitosis because caldesmon inhibits actomyosin ATPase,
and because caldesmon, together with tropomyosin, regulates the actin
severing and capping activities of gelsolin. We will biochemically
characterize how the mitosis-specific phosphorylation of caldesmon changes
microfilament assembly and actomyosin interactions in vitro. In vivo
functions of mitosis-specific phosphorylation of caldesmon will be explored
through microinjection of phosphorylated caldesmon, antibodies that block
phosphorylation or dephosphorylation, and mutant caldesmons lacking the
phosphorylation sites, into cultured cells. We will observe whether the
microinjection will perturb the assembly of microfilaments during mitosis
and other cell cycle stages. We will examine changes in the phosphorylation
state of caldesmon during cell cycle progression in detail to see whether
the phosphorylation of caldesmon correlates with changes in microfilament
assembly. Because transformed cells show morphological alterations similar
to those found in mitotic cells, we will examine, using ts Rat-I cells,
whether caldesmon is phosphorylated during cell transformation. Finally,
because we have found that cdc2 kinase (mitosis promotion factor) is one
of two kinase activities that phosphorylate caldesmon during mitosis, we
will characterize how cdc2 kinase and the other kinase activity
phosphorylate caldesmon. We will also search for other
microfilament-associated proteins that are phosphorylated by these kinases
during mitosis. Because cell cycle control is intimately related to cell
transformation, the proposed studies will help us understand not only how
cells divide, but also why cancer cells lose control of cell division.
Effective start/end date1/1/9212/31/99


  • National Cancer Institute
  • National Cancer Institute
  • National Cancer Institute
  • National Cancer Institute
  • National Cancer Institute


  • Cell Biology


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