| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2005: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2004: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
Loss of contact with substratum triggers apoptosis in many normal cell types, a phenomenon termed anoikis. We found that mitogen-activated protein /extracellular signal-regulated kinase kinase (MEK) inhibitors induced apoptosis in two human breast cancer cells when nonanchored, while anchored cells remained viable. To analyze the biochemistry behind this event, we measured the amounts of Bcl-2 family proteins. Upon treatment with MEK inhibitors, BimEL in these cells rapidly increased, irrespective of the state of anchorage. However, it translocated to mitochondria only in nonanchored cells, explaining why attached cells remain viable. The two sensitized cell lines had exceedingly low basal levels of BimEL compared to other breast cancer cell lines, suggesting that maintenance of low BimEL amount, is important for survival of these cell lines. MEK inhibitors also induced the electrophoretic mobility shift of BimEL, indicative of reduced phosphorylation. In vitro, BimEL was phosphorylated by extracellular signal-regulated kinase (ERK) on serine 69, which resides in the BimEL-specific insert region. Using phosphospecific antibody against this site, we showed that this residue is actually phosphorylated in cells. We also showed that phosphorylation of senile 69 promotes ubiquitination of BimEL. We conclude that MEK inhibitors sensitize certain cancer cells to anoikis by blocking phosphorylation and hence degradation of BimEL, a mechanism which these cells depend on to escape anoikis. Our results also imply a role for BimEL as a biochemical marker for prognosis and diagnosis of efficacy of MEK inhibitors.
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