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Bruce Torbett

Affiliation: Scripps
Associate Professor Departments of Molecular and Experimental Medicine and Immunology

Head, Molecular and Cellular Therapy Scripps Cancer Center
Phone: 858-784-9123


Ph.D., UCLA, 1988

Research Summary

Our main research interests are focused in three areas; defining PU.1 transcription factor partners critical for normal and abnormal differentiation of myeloid cells, understanding HIV-1 protease inhibitor resistance through molecular evolution, and the use of HIV-1 vectors to deliver novel viral inhibitors to human hematopoietic cells to impart an anti-HIV- 1 effect during development.


PU.1, an ets family transcription factor member is only expressed in hematopoietic cells, is critical for dictating myeloid development, and required for regulating genes required for monocyte/macrophage and neutrophil function. PU.1 gene-disrupted mice are devoid of B and dendritic cells, monocytes/macrophages, and mature neutrophils, but not T cells.

To define which parts of PU.1 promote myeloid development, we have utilized PU.1 gene- disrupted hematopoietic cells that are obtained from our PU.1 null mouse, followed by HIV- 1 vector delivery of PU.1 domain-mutants to effectively restore PU.1 function. This approach is allowing us to pinpoint PU.1 domains required for monocyte and granulocyte differentiation. This strategy should also allow a proteomics based methodology to isolate and characterize transcription factors that interact with PU.1 at various stages of development.


Viral protease is responsible for processing the viral proteins that are implicated in producing infectious virus. Blocking protease function inhibits viral production and reduces viral spread. Protease inhibitors suppress HIV-1 replication to mostly undetectable levels in patients. However, HIV-1 variants evolve that escape drug-treatment by developing resistance.

To better understand the sequence of protease (pictured to the left) structural changes required for the development of inhibitor resistance, we have generated a panel of protease inhibitor resistant proteases varying in their degree of resistance. These protease mutants are used to structurally and biochemically define determinates that impart resistance. To define structural changes in protease during the development of resistance, RNA aptamer libraries are being produced to probe structure and peptide substrate libraries will be used to define the biochemistry of substrate specificity.


Our group has generated improved HIV-1 vectors that are capable of sustained gene expression in many primary human cell types. We are now in the process of evaluating, in hematopoietic stem cells and CD4 T cells, the biological and virological effects of CCR5- intrabody genes and other novel molecular strategies, such as siRNA and ribozymes, delivered by one of our HIV-1 vectors. The CCR5-intrabody restricts cell surface expression of the HIV-1 co-receptor CCR5 and thus renders cells expressing the CCR-5-intrabody immune to HIV-1 infection by CCR5 using viruses. siRNA and ribozyme strategies are directed at controlling the regulation of nef and protease genes.


References From PubMed (NCBI)


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©2008 UCSD/Burnham Molecular Pathology Graduate Program