Cancer often develops through the disruption of proper responses to extracellular signals. Thus, understanding how normal cells sense and generate proper responses to changes in environment is important. Normally, transduction of extracelluar signals into cellular responses involves a cascade of biochemical events that eventually induce gene expression. These events are mediated by transcription factors (TF), a class of DNA-binding proteins that dictate the nature of genes expressed. Deregulation of TF activities by genetic and epigenetic anomalies can lead to amplification of disrupted cellular responses via uncontrolled gene expression. Activation of a critical TF, NF-kappaB, by extracellular signals normally occurs only transiently since NF-kappaB activates synthesis of its own inhibitor, IkappaBalpha, which enters the nucleus, removes NF-kappaB from DNA binding sites, and exports it out to the cytoplasm to terminate NF-kappaB function. By contrast, deregulation of NF-kappaB activity, frequently seen in human cancers, must counteract this feedback mechanism to maintain constitutive (constant) NF-kappaB activation to sustain survival and induce chemo/radioresistance. Research in this laboratory has demonstrated that murine B cells, a rare example with non-pathological constitutive NF-kappaB activation, maintain such activity by degrading newly synthesized IkappaBalpha via a previously uncharacterized mechanism. Our preliminary data also suggest that in order for continual degradation of IkappaBalpha to occur, there is a requirement that newly formed, nuclear NF-kappaB/IkappaBalpha complexes must be exported out to the cytoplasm in both murine B cells and human cancer cells. Thus, the proposed research will test the hypothesis that constitutive NF-kappaB activation requires a mechanism to counteract the autoinhibitorv feedback regulation imposed by its inhibitor IkappaBalpha.
In Aim 1, mutational analysis will be employed to delineate novel IkappaBalpha degradation mechanisms.
Under Aim 2, the functional role of the nuclear export of IkappaBalpha will be determined in both maintenance of constitutive NF-kappaB activation and survival of human cancer cells.
Aim 3 will test the in vivo roles of nuclear export of IkappaBalpha in B cell development by the generation of mice harboring IkappaBalpha loci with N-NES point mutations. This research program will help define fundamental mechanisms critical for constitutive NF-kappaB activation in B cell development and human malignancies. They may also reveal N-NES-mediated nuclear export of IkappaBalpha as a rational therapeutic target to generally disrupt constitutive NF-kappaB activation to induce cell death or chemo/radiosensitization in human cancer.
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