Characterization of PRL-1 and PRL-2 as human oncogenes

Sean Richard Werner, Purdue University

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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