Biochemistry and Biophysics - UNC School of Medicine
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Ann Erickson, PhD
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RESEARCH INTERESTS:
Cellular Biochemistry: Secretion of Lysosomal Proteases by Transformed Cells
In many tumors, the synthesis and secretion of a particular lysosomal protease is increased relative to normal cells in the surrounding tissue. The secreted protease is thought to aid tumor cell metastasis by participating in the degradation of the extracellular matrix through which the cells must migrate in order to establish secondary tumors. During certain developmental processes such as spermatogenesis, normal cells also need to migrate. There is evidence of increased expression and secretion of lysosomal proteases during this process too. We hope to characterize this lysosomal enzyme secretion pathway and determine the structural signals that are responsible for moving enzymes normally stored intracellularly in lysosomes into the extracellular environment, where they may serve physiological functions not normally ascribed to lysosomal proteases.
In Kirsten-virus transformed mouse fibroblasts (KNIH), synthesis of the lysosomal cysteine protease procathepsin L is upregulated and significant quantities of the inactive proform of the protease, normally a transient precursor, are stored within cells. By electron microscopy, we have localized the intracellular proenzyme to Golgi stacks and to abundant large, dense-core multivesicular endosomes. Procathepsin L reaches these vesicles after undergoing self-aggregation in the trans Golgi, a step that requires the propeptide. The extensive precedent for secretion of the contents of multivesicular endosomes suggests that in response to signals, these protease-containing endosomes might fuse with the plasma membrane, a process that would dump a bolus of protease in a localized region outside a cell.
To understand the change in cellular targeting that occurs when synthesis of the protease increases, we are identifying cellular proteins that bind procathepsin L and thus potentially contribute to targeting the protease into the dense-core storage vesicles. We are also generating mutant forms of the lysosomal protease that fail to bind these cellular proteins in order to determine where the mutant proteins accumulate in cells due to a block in their targeting pathway. These studies, which utilize mammalian cell culture, molecular biology, polyacrylamide gel electrophoresis, western blotting, cell fractionation, immunofluorescence, affinity chromatography and yeast two-hybrid analysis, will help us understand the structural signals which are responsible for moving enzymes normally targeted to lysosomes into the extracellular environment.
RECENT PUBLICATIONS:
Bocock, J. P., Carmicle-Davis, S., Chhotani, S., Ruffolo, M., Chu, H. and Erickson, A.H. (2009) The PA-TM-RING protein RNF13 is an endosomal integral membrane E3 ubiquitin ligase whose RING finger domain is released to the cytoplasm by proteolysis. FEBS J. in press.
Erickson, A.H. and Bocock, J.P. (2007). Targeting to lysosomes in mammalian cells: the biosynthetic and endocytic pathways. Methods Mol. Biol. 390, 339-361.
Nepal, R.M., Mampe, S., Shaffer, B., Erickson, A.H., and Bryant, P. (2006). Cathepsin L maturation and activity is impaired in macrophages harboring M. avium and M. tuberculosis. Int. Immunol. 18, 931-939.
Collette, J., Bocock, J.P., Ahn, K., Chapman, R.L., Godbold, G., Yeyeodu, S., and Erickson, A.H. (2004). Biosynthesis and alternate targeting of the lysosomal cysteine protease cathepsin L. Int. Rev. Cytol. 241, 1-51.
Collette, J., Ulku, A.S., Der, C.J., Jones, A., and Erickson, A.H. (2004). Enhanced cathepsin L expression is mediated by different Ras effector pathways in fibroblasts and epithelial cells. Int. J. Cancer 112, 190-199.
Bocock, J.P., Edgell, C.J., Marr, H.S., and Erickson, A.H. (2003). Human proteoglycan testican-1 inhibits the lysosomal cysteine protease cathepsin L. Eur. J. Biochem. 270, 4008-4015.
Ahn, K., Yeyeodu, S., Collette, J., Madden, V., Arthur, J., Li, L., and Erickson, A.H. (2002). An alternate targeting pathway for procathepsin L in mouse fibroblasts. Traffic. 3, 147-159.
Yeyeodu, S., Ahn, K., Madden, V., Chapman, R., Song, L., and Erickson, A.H. (2000). Procathepsin L self-association as a mechanism for selective secretion. Traffic. 1, 724-737.