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UBC Theses and Dissertations

The role of the protein tyrosine phosphatase PRL-3 in regulating cell signaling in cancerous and non-cancerous cell lines Bessette, Darrell Christopher


Protein tyrosine phosphorylation is an important mechanism that regulates complex intracellular signaling pathways that determine many cellular activities, such as proliferation, growth, and differentiation. Phosphorylation is regulated by the concerted activities of protein tyrosine kinases and protein tyrosine phosphatases (PTPs), which respectively add and remove phosphate to and from proteins. PRL-3 is a member of a novel subfamily of PTPs that possess prenylation motifs at the C-terminus, thus effecting membrane targeting of these proteins. High PRL-3 expression is an indicator of disease progression and poor prognosis in a number of carcinomas. While some of the biology of PRL-3 has been determined, the molecular mechanisms by which PRL-3 can impart enhanced malignancy to cells and tumours, and the means by which it is upregulated in these cancers are not well understood. I established three independent cell systems to investigate the role of PRL-3 in signaling: an inducible system expressing wild-type and catalytically-inactive Flag-tagged PRL-3 in HEK 293 (293) cells, a constitutive system expressing EGFP-tagged wild-type, catalytically-inactive and prenylation-deficient PRL-3 in LNCaP prostate carcinoma cells, and a shRNA-mediated stable knockdown of PRL-3 in LNCaP, C4-2 and DU-145 prostate carcinoma cells. I examined the effect of altering PRL-3 expression in these cell systems upon phenotypic characteristics of proliferation, migration, and invasion, and on modulating the expression or activation of a number of signaling molecules. PRL-3 was found to promote invasion and/or migration of 293 and prostate carcinoma cells. PRL-3 limited the proliferation of LNCaP cells, but had no effect on the proliferation of the other cell types. PRL-3 expression reduced E-cadherin expression in 293 cells but did not alter this or other EMT marker expression in prostate cancer cells. While PRL-3 expression had little effect on cell signaling in untreated 293 or prostate cancer cells, iii overexpression of PRL-3 in growth factor-stimulated 293 cells regulated Mek-dependent Erk activity. PRL-3 localized at the plasma membrane with adherens junction proteins but did not alter E-cadherin, β- catenin or α-catenin expression or interactions. These studies support the findings that PRL-3 imparts metastasis-associated properties upon different cell types but the molecular mechanisms behind this behaviour remain unresolved.

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