PRL Phosphatases: Expression and Function in Pancreatic Cancer

Résumé du livre

One of thecurrent goals in cancer research is to discover and validate novel molecular targets that may be useful for diagnostic and therapeutic purposes in fighting this disease. The PRL phosphatases (PRL-1, PRL-2, and PRL-3) are low molecular weight protein tyrosine phosphatases with unknown biological function(s) that have gained attention from cancer researchers in the past couple of years, mainly due to reports that these phosphatases may play important roles in tumor progression and metastasis. Motivated by the particular urgent need for molecular targets in pancreatic cancer this work was undertaken to determine what role PRL proteins played in pancreatic cancer biology and to determine if targeting PRLs would be effective in treating this disease. In this dissertation, it was found that both PRL-1 and PRL-2, but not PRL-3 are upregulated in pancreatic adenocarcinomas, suggesting that some cancer cells are dependent upon their activity for continued proliferation and survival. To validate this hypothesis, siRNAs were used in cell-based assays to evaluate the biological consequences of PRL-1 and/or PRL-2 inhibition. It was found that perturbations in PRL phosphatase signaling result in reduced proliferation, migration and especially the ability to grow in soft agar. Oligonucleotide microarray analysis revealed that many Erk and/or Akt dependent stress and growth factor inducible genes were differentially regulated between pancreatic cancer cells treated with PRL-targeting siRNA and their non-targeting siRNA treated counterparts. Subsequently, PRL knockdown was found to alter serum induced as well as amino acid deprivation induced Akt and Erk phosphorylation in multiple pancreatic cancer cell lines, suggesting that PRLs function upstream of these key pathways. Interestingly, we show that PRL proteins in cell free assays exhibit higher activity on doubly phosphorylated phosphatidylinositol substrates than tyrosine-phosphorylated peptides, suggesting that the biological substrate(s) might include non-protein molecules. These data support the hypothesis that PRL-1 and PRL-2 might play important biological roles in pancreatic cancer cells and further studies should be undertaken to determine the usefulness of these phosphatases as potential molecular biomarkers and targets.