Characterization of PRL-1 and PRL-2 as human oncogenes
Abstract
One of the current goals in cancer research is to find molecular targets which may be exploited in the fight against the disease. A novel family of proteins which are currently being investigated as potential targets is the PRL family of phosphatases. This family consists of PRL-1, PRL-2 and PRL-3. These enzymes contain a consensus tyrosine phosphatase domain and have been shown to dephosphorylate artificial tyrosine-phosphorylated substrates in vitro. Given the observations that increased levels of PRL phosphatases leads to a cancerous phenotype, it is our hypothesis that; (1) increased PRL-1 and PRL-2 levels lead to changes in cell cycle regulatory proteins, (2) that increased levels of PRL-1 and/or PRL-2 can be found in human cancers, and (3) decreasing PRL-1 or PRL-2 can reduce the cancerous phenotype in breast cancer cells. We found that increased PRL-1 and PRL-2 protein is accompanied by a reduced amount of time spent in G1 after serum-starvation synchronization. Additionally, protein levels of the cyclin dependent kinase inhibitor p21 Cip1/Waf1 are decreased in cells overexpressing either PRL-1 or PRL-2. The levels of cyclins D, B, and E are unaffected by increased PRL-1 or PRL-2 expression but cyclin A increases in response to increased PRL-1. The kinase activity of the p21Cip1/Waf1 target CDK2 is increased 42% and 15% respectively by increased PRL-1 and PRL-2 protein. In multiple human cancers PRL-1 and PRL-2 protein is upregulated compared to corresponding normal tissue or the average expression across tissue types and samples. When specifically targeted for RNA-interference mediated inhibition of PRL-2, the breast cancer cell lines T47D, ZR75-1, and BT549 exhibit significantly reduced rates of proliferation over a six day period. This reduction in proliferation is accompanied by reductions of S-phase populations and DNA synthesis as well as increases in the level of p21Cip1/Waf1. Apoptosis was not found to be increased in PRL-1 or PRL-2-overexpressing cells, but in cells with RNAi mediated PRL-2 reduction, apoptosis was increased. These new aspects of PRL-1 and PRL-2 biology support the hypothesis that these enzymes may prove to be useful targets in the fight against cancer.
Degree
Ph.D.
Advisors
Crowell, Purdue University.
Subject Area
Cellular biology|Oncology
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