Abstract
818
Recent evidence has implicated an oncogenic function for the PRL family of phosphatases. The mechanism for oncogenic transformation by these phosphatases has yet to be described. We tested the hypothesis that increased expression of these phosphatases leads to altered progression through the cell cycle. Non-synchronized epithelial cells overexpressing PRL-1 or PRL-2 exhibited an increased proportion of the population in S-phase. These cells demonstrate a shortened transition to S-phase after release from a serum-starvation induced G1 block. Furthermore, expression of the cyclin dependent kinase inhibitor p21 was significantly reduced in cells that overexpressed PRL-1 or PRL-2 while CDK-2 histone phosphorylation was increased. With mounting evidence that altered expression of these phosphatases leads to a transformed phenotype in cell culture models, we tested the hypothesis that PRL phosphatases are expressed at higher levels in human tumor vs. normal tissues. To evaluate the expression patterns of PRL-1 in human cancer, we performed immunohistochemistry on human tissue sections with an anti-PRL-1 antibody. PRL-1 protein levels were found to be elevated in breast (33%, 1/3) and ovarian cancers (33%, 3/10) compared to matched normal tissue, and expressed at high levels in pancreatic (25%, 2/8) cancers. PRL-1 protein levels in cancer tissues were also measured by immunohistochemistry using an NCI cancer tissue array, TARP 3. This array provided a higher sample number but does not contain matched tumor and normal tissues. Protein levels were detected at elevated levels in breast (24%) ovarian (32%) colon (31%) and prostate (55%) cancers vs. reference normal tissue. Taken together, these results suggest that overexpression of the oncogenic PRL tyrosine phosphatase PRL-1 occurs in a substantial proportion of human cancers and that PRL phosphatases may represent novel molecular targets for cancer therapy.
- American Association for Cancer Research
Volume 64, Issue 7 Supplement
