Brandon White, PhD

Assistant Professor
Department of Biological Sciences


San José State University
Department of Biological Sciences
One Washington Square
San José, CA 95192-0100
Duncan Hall, Room 644

Telephone: (408) 924-4839 FAX: (408) 924-4840

E-mail: bwhite@science.sjsu.edu




Education

B.S. 1991 Auburn University
Ph.D. 2001 University of Alabama at Birmingham

Research

My research interests center around transcriptional and signal transduction pathways in normal and diseased states. The lab works on understanding notch-signaling pathway, which plays important roles in cell fate decisions, and more recently has been identified to play roles in maintenance of terminally differentiated cell types. In the presence of cells expressing the Jagged, Serrate, or Delta ligands, the Notch transmembrane receptor undergoes sequential proteolytic cleavage steps that ultimately releases the intracellular domain (ICD) from the membrane. The ICD enters the nucleus and interacts selectively with members of the CSL (CBF-1, Suppressor of Hairless, LAG-1) family of enhancer-binding proteins to activate transcription of various genes. Recent studies have identified Mastermind (MAM), a protein that interacts with the ICD and has shown to be required for activation of notch responsive genes. In the absence of Notch ICD, CSL proteins recruit repressor complexes preventing these genes from being expressed. Identified target genes of Notch signaling include basic helix-loop-helix proteins that promote cell differentiation, such as Drosophila Enhancer of split or mammalian Hairy Enhancer of Split genes, HES-1 and HES-5. Very few mammalian target genes have been identified to date. Recently, reports have shown that in various leukemias and leukemic cell lines, mutations were identified in the Notch ICD that resulted in frame-shifts deleting the C-terminal domain, which appears to be important in the rapid turnover of the Notch ICD. In the absence of this domain, the Notch protein becomes very stable and it is thought that this stability is a contributing factor to the ability of Notch to promoter tumor formation


Potential Projects are summarized as follows:


1) Biochemical characterization of Mastermind and Notch protein modifications. I have shown in my post-doctoral fellowship that Mastermind recruits the kinase CDK8 to phosphorylate the Notch ICD and this phosphorylation results in ubiquitination and degradation of the Notch ICD. Recently, I identified that the mastermind protein is also ubiquitinated in vivo, yet not degraded like the ICD. This ubiquitination is important for transcriptional regulation of notch target genes by mastermind as mutations of certain lysine residues decrease transcriptional activity of Notch reporter genes. Ubiquitination in transcriptional regulation has recently been shown to be very important in genes that are tightly controlled. A major goal of this research will be to take the constructs generated and introduce them into a transgenic mouse system to determine how these point mutants may result in cancer in an animal model system.


2) Notch signaling in apoptosis and cancer. Emerging studies have supported a role for dysregulated or constitutive Notch signaling in T-cell acute lymphoblastic leukemia (T-ALL), which accounts for 25% of adult ALLs as well as a significant number of pediatric ALLs. In rare cases, a chromosomal translocation induces the expression of a constitutively active and truncated Notch1 protein (called TAN-1), which is capable of inducing T cell lymphomas in mice when transduced in bone-marrow cells. Even more importantly, the Notch3 protein was recently found to be over-expressed in virtually all cases of T-ALL. Interestingly, Notch signaling appears to be essential both for initiation of leukemogenesis as well as for the growth and survival of T-ALLs. Disrupting Notch signaling by means of presenilin inhibitors or with a dominant-negative version of the Notch co-activator, Mastermind, causes Notch1-transformed T-ALL cell lines to undergo growth suppression and apoptosis, indicating that Notch signaling is continuously required for transformation.

The mechanism by which Notch signaling contributes to cell transformation is not precisely understood, however the transformation is accompanied by over-expression of at least some of the known Notch target genes. Recent studies also indicate that notch may regulate the Myc transcription factor. Myc was first identified as an oncogene. Because the Notch transcription complex plays a major role in human leukemias and other tumors, it will be important to characterize the mechanism of Notch transactivation in detail to better define the function of the Notch proteins and identify new Notch-associated co-activators, which may provide useful targets for inhibition of Notch signaling in transformed cells.


There is also increasing evidence in the literature that Notch may play roles in Prostate Caner, Breast Cancer, and Lung Cancers. Research would focus on Prostate and Lung Cancers initial and studies would be basic characterizations of established cell lines to determine the level and activity of Notch Proteins. If results look promising, further studies would be conducted to determine if mutations exist in the Notch or Mastermind Proteins


Portions of the research done in the lab are supported by the grant of a Veritas Luminometer from Turner BioSystems.

Current Courses

 

 
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