Faculty Research: Brian Ashburner
Associate Professor
Associate Dean, College of Natural Sciences and Mathematics
Director, UToledo-Salford Exchange Program
Postdoctoral Research Fellow, Lineberger Comprehensive Cancer Center,
University of North Carolina, Chapel Hill, NC
Ph.D. Loyola University of Chicago, 1995
B.A., St. Anselem College, Manchester, NH
Office: WO 3213B
Phone No: 419.530.1542
Email: brian.ashburner@utoledo.edu
Research
My lab is interested in the regulatory mechanisms controlling the activity of the transcription factor NF-kB. NF-kB (Nuclear Factor –kappa B) regulates a number of different cellular processes including immune and inflammatory responses, apoptosis, and cell cycle progression and differentiation. Dysregulation of NF- kB is associated with many diseases including cancer, atherosclerosis, chronic inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease, and many viral infections.
NF-kB was first identified as a nuclear factor in B cells required for expression of the immunoglobulin kappa light chain gene. Subsequently, NF-kB was found to be a ubiquitously expressed and highly conserved transcription factor, with homologues found in many organisms. The regulatory mechanism controlling NF-kB activity is unique in that NF-kB is found primarily in the cytoplasm in an inactive state bound by its inhibitory proteins, members of the IkB family. Activation of NF-kB occurs in response to a number of different stimuli including inflammatory cytokines, bacterial and viral infection, UV and gamma irradiation, and certain chemotherapeutic drugs. Stimulation of cells with any of these agents leads to phosphorylation, ubiquitination, and subsequent degradation of the IkB inhibitory protein. This results in the release of NF-kB and subsequent translocation to the nucleus where it activates expression of its target genes. Given the many important processes that NF-kB is involved in, it is important to understand the varied mechanisms controlling the activity of this transcription factor.
The primary focus of my lab is to understand how transcriptional coactivator and corepressor proteins regulate the transcriptional activity of NF-kB. Transcriptional coregulatory proteins do not bind directly to DNA, but instead interact with sequence-specific transcription factors to enhance or repress their ability to activate transcription. Chromatin structure is generally thought to be repressive to transcription and therefore this repression must be overcome in order to activate transcription. In support of this, many coactivator and corepressor proteins function by modulating chromatin structure. The CBP/p300 coactivators have previously been shown to be required for NF-kB-dependent transcriptional activity. These coactivators, like several others, possess intrinsic histone acetyltransferase activity. When recruited to a promoter by a transcription factor, CBP/p300 can transfer an acetyl group to lysine residues in the amino-terminal tails of the core histones. Acetylation of the histones reduces the affinity of DNA for the nucleosome and results in increased access of transcription factors to their DNA binding sites. In contrast, many corepressor proteins possess histone deacetylase (HDAC) activity. When HDAC proteins are recruited to the promoter, they deacetylate the amino-terminal tails of the core histones, allowing the chromatin to once again assume its repressive state.
Current research in my lab is focused on the following three broad areas related to the control of NF-kB activity by transcriptional coregulatory proteins.
Identification of novel NF-kB-interacting transcriptional coactivator and corepressor
proteins. We recently performed a cytoplasmic yeast-two hybrid screen to identify new coregulatory
proteins that function to regulate NF-kB activity. Through this screen we identified
the product of the DEK proto-oncogene as a transcriptional corepressor of NF-kB activity
and the Spermidine/Spermine N1-Acetyltransferase-2 (SSAT2) protein as a transcriptional
coactivator of NF-kB. Ongoing and future work is focused on further elucidating the
mechanisms by which these proteins function to regulate NF-kB activity.
Regulation of NF-kappaB activity through p38 MAP kinase-mediated modulation of the
CBP coactivator protein. The second project we are focused on involves understanding how the p38 MAP kinase
regulates the transcriptional activation function of the p65 subunit of NF-kB. Although
it is well established that p38 plays an important role in mediating the activation
of NF-kB in response to many signals, the mechanism by which p38 targets NF-kB is
not yet understood. Evidence from our lab indicates that p38 does not directly target
NF-kB. Instead, p38 can interact with and phosphorylate the CBP coactivator protein.
CBP is an essential coactivator for NF-kB and inhibition of p38 kinase activity reduces
the amount of CBP that interacts with the p65 subunit of NF-kB. Thus it appears that
p38 regulates the activity of NF-kB by targeting an essential coactivator protein.
Characterization of the role of the Class I histone deacetylase (HDAC) proteins in regulation of NF-kappaB activity. Previously we, and others had shown that the Class I histone deacetylases; HDAC1, HDAC2, and HDAC3 function to repress the ability of NF-kB to activate transcription. To further analyze the function of these corepressors in regulation of NF-kB activity we have established a lentiviral system to inducibly express shRNAs to specifically knockdown expression of each of these proteins. Ongoing experiments are focused on understanding the individual roles of each of these proteins in mediating the repression of NF-kB activity.