Anthrax toxin proteins from Bacillus anthracis constitute a highly efficient system for delivering cytotoxic enzymes to the cytosol of tumor cells. However, exogenous proteins delivered to the cytosol of cells are subject to ubiquitination on lysines and proteasomal degradation, which limit their potency. We created fusion proteins containing modified ubiquitins with their C-terminal regions fused to the Pseudomonas exotoxin A catalytic domain (PEIII) in order to achieve delivery and release of PEIII to the cytosol. Fusion proteins in which all seven lysines of wild-type ubiquitin were retained while the site cleaved by cytosolic deubiquitinating enzymes (DUBs) was removed were nontoxic, apparently due to rapid ubiquitination and proteasomal degradation. Fusion proteins in which all lysines of wild-type ubiquitin were substituted by arginine had high potency, exceeding that of a simple fusion lacking ubiquitin. This variant was less toxic to nontumor tissues in mice than the fusion protein lacking ubiquitin and was very efficient for tumor treatment in mice. The potency of these proteins was highly dependent on the number of lysines retained in the ubiquitin domain and on retention of the C-terminal ubiquitin sequence cleaved by DUBs. It appears that rapid cytosolic release of a cytotoxic enzyme (e.g., PEIII) that is itself resistant to ubiquitination is an effective strategy for enhancing the potency of tumor-targeting toxins.
Pubmed ID: 23631917 RIS Download
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A research program of the NIA which focuses on neuroscience, aging biology, and translational gerontology. The central focus of the program's research is understanding age-related changes in physiology and the ability to adapt to environmental stress, and using that understanding to develop insight about the pathophysiology of age-related diseases. The IRP webpage provides access to other NIH resources such as the Biological Biochemical Image Database, the Bioinformatics Portal, and the Baltimore Longitudinal Study of Aging.
View all literature mentionsCell line RAW 264.7 is a Cancer cell line with a species of origin Mus musculus
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