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      Possible regulation of growth and tumorigenic properties of cancer by ankyrin 105

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      Mpofu-final-thesis.pdf (4.042Mb)
      Date
      2010-06
      Author
      Mpofu, Christopher
      Type
      Thesis
      Degree Level
      Masters
      Metadata
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      Abstract
      Receptor tyrosine kinases (RTKs) are integral membrane proteins that regulate many functions including cell proliferation, cell survival, and cell death. They have been shown to be responsible for the uncontrolled growth of several cancers. RTKs phosphorylate downstream targets such as phosphatidylinositol 3 kinase (PI3K), a lipid kinase that is made up of two major subunits—p85 and p110. Receptor-mediated endocytosis delivers RTKs from the plasma membrane to late endosomes and lysosomes for degradation. This process is controlled by ESCRT proteins and Rab7. PI3K associates with PDGFR during endocytosis, and PI3K binding sites are necessary for the lysosomal trafficking of PDGFR. The smaller isoforms of the ankyrin 3 (Ank3) proteins bind p85. Ank3 overexpression was shown to increase PDGFR degradation, perhaps by controlling the targeting of PDGFR to late endosomes and lysosomes. Ank3 overexpression also reduced the RTK levels and cell proliferation rates of NIH 3T3 cells. We sought to investigate if cancer cells with RTK overexpression might be deficient in Ank3, and if overexpression of ankyrin 105 (Ank105), one of the smaller isoforms of Ank3, would reduce RTK levels and the tumorigenic properties of cancer cells. Two brain cancer cell lines showed reduced Ank105 levels associated with high RTK levels, while high levels of Ank105 associated with low RTK levels were found in normal brain cells. This suggested a loss of Ank105 in the cancer cells, which may have played a role in the cancer development process. We observed reduced RTK levels and anchorage-independent growth in cancer cells overexpressing HA-Ank105, however, most cells overexpressing a blank vector also showed the same results. An independent effect of the overexpression process was thought to play a role in influencing cell behavior. In the lung cancer cell line HCC827, however, there was significant reduction of anchorage-independent growth that was specific for HA-Ank105. There also appeared to be a significant reduction in the cell proliferation rate of T98G brain cancer cells following transfection with HA-Ank105. Furthermore, those cells overexpressing HA-Ank105 tended to die early in tissue culture, with those that survived losing their HA-Ank105 expression. Overall our results suggest a possible role for Ank105 in downregulating RTK levels and growth properties of cancer cells.
      Degree
      Master of Science (M.Sc.)
      Department
      Biochemistry
      Program
      Biochemistry
      Supervisor
      Anderson, Deborah
      Committee
      Chelico, Linda; Ovsenek, Nick; Khandelwal, Ramji L.; Roesler, William J.
      Copyright Date
      June 2010
      URI
      http://hdl.handle.net/10388/etd-05312010-222624
      Subject
      receptor tyrosine kinase
      ankyrin 105
      adenovirus
      transfection
      transduction
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      • Graduate Theses and Dissertations
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