Tissue-specific alterations of PRL-1 and PRL-2 expression in cancer.

The PRL-1 and PRL-2 phosphatases have been implicated as oncogenic, however the involvement of these molecules in human neoplasms is not well understood. To increase understanding of the role PRL-1 and PRL-2 play in the neoplastic process, in situ hybridization was used to examine PRL-1 and PRL-2 mRNA expression in 285 normal, benign, and malignant human tissues of diverse origin. Immunohistochemical analysis was performed on a subset of these. PRL-1 and PRL-2 mRNA expression was also assessed in a small set of samples from a variety of diseases other than cancer. Where possible, associations with clinicopathological characteristics were evaluated. Alterations in PRL-1 or -2 expression were a frequent event, but the nature of those alterations was highly tumor type specific. PRL-1 was significantly overexpressed in 100% of hepatocellular and gastric carcinomas, but significantly under-expressed in 100% of ovarian, 80% of breast, and 75% of lung tumors. PRL-2 expression was significantly increased in 100% of hepatocellular carcinomas, yet significantly downregulated in 54% of kidney carcinomas. PRL-1 expression was correlated to patient gender in the bladder and to patient age in the brain and skeletal muscle. PRL-1 expression was also associated with tumor grade in the prostate, ovary, and uterus. These results suggest a pleiotropic role for PRL-1 and PRL-2 in the neoplastic process. These molecules may associate with tumor progression and serve as clinical markers of tumor aggressiveness in some tissues, but be involved in inhibition of tumor formation or growth in others.

Cell cycle arrest by the isoprenoids perillyl alcohol, geraniol, and farnesol is mediated by p21(Cip1) and p27(Kip1) in human pancreatic adenocarcinoma cells.

Pancreatic cancer, the fourth leading cause of cancer-associated mortality in the United States, usually presents in an advanced stage and is generally refractory to chemotherapy. As such, there is a great need for novel therapies for this disease. The naturally derived isoprenoids perillyl alcohol, farnesol, and geraniol have chemotherapeutic potential in pancreatic and other tumor types. However, their mechanisms of action in these systems are not completely defined. In this study, we investigated isoprenoid effects on the cell cycle and observed a similar antiproliferative mechanism of action among the three compounds. First, when given in combination, the isoprenoids exhibited an additive antiproliferative effect against MIA PaCa-2 human pancreatic cancer cells. Furthermore, all three compounds induced a G(0)/G(1) cell cycle arrest that coincided with an increase in the expression of the cyclin kinase inhibitor proteins p21(Cip1) and p27(Kip1) and a reduction in cyclin A, cyclin B1, and cyclin-dependent kinase (Cdk) 2 protein levels. Immunoprecipitation studies demonstrated increased association of both p21(Cip1) and p27(Kip1) with Cdk2 as well as diminished Cdk2 kinase activity after isoprenoid exposure, indicating a cell cycle-inhibitory role for p21(Cip1) and p27(Kip1) in pancreatic adenocarcinoma cells. When siRNA was used to inhibit expression of p21(Cip1) and p27(Kip1) proteins in MIA PaCa-2 cells, conditional resistance to all three isoprenoid compounds was evident. Given similar findings in this cell line and in BxPC-3 human pancreatic adenocarcinoma cells, we conclude that the chemotherapeutic isoprenoid compounds perillyl alcohol, farnesol, and geraniol invoke a p21(Cip1)- and p27(Kip1)-dependent antiproliferative mechanism in human pancreatic adenocarcinoma cells.

Cellular localization of PRL-1 and PRL-2 gene expression in normal adult human tissues.

Recent evidence suggests that the PRL-1 and -2 phosphatases may be multifunctional enzymes with diverse roles in a variety of tissue and cell types. Northern blotting has previously shown widespread expression of both transcripts; however, little is known about the cell type-specific expression of either gene, especially in human tissues. Therefore, we investigated expression patterns for PRL-1 and -2 genes in multiple normal, adult human tissues using in situ hybridization. Although both transcripts were ubiquitously expressed, they exhibited strikingly different patterns of expression. PRL-2 was expressed heavily in almost every tissue and cell type examined, whereas PRL-1 expression levels varied considerably both between tissue types and between individuals. Widespread expression of PRL-1 and -2 in multiple organ systems suggests an important functional role for these enzymes in normal tissue homeostasis. In addition, the variable patterns of expression for these genes may provide distinct activities in each tissue or cell type.

Cyclooxygenase-2 expression in hamster and human pancreatic neoplasia.

Cyclooxygenase-2 (COX-2) has been implicated in the development of gastrointestinal malignancies. The aim of the present study was to determine COX-2 expression/activity throughout stages of experimental and human pancreatic neoplasia. COX-2 immunohistochemistry was performed in pancreata of hamsters subjected to the carcinogen N-nitrosobis-(2-oxopropyl)amine (BOP) and in human pancreatic tumors. COX-2 activity was determined by prostaglandin E2 assay in tumor versus matched normal pancreatic tissues. The activity of the COX inhibitor sulindac was tested in the PC-1 hamster pancreatic cancer model. COX-2 expression was elevated in all pancreatic intraepithelial neoplasias (PanINs) and adenocarcinomas. In BOP-treated hamsters, there were significant progressive elevations in COX-2 expression throughout pancreatic tumorigenesis. In human samples, peak COX-2 expression occurred in PanIN2 lesions and remained moderately elevated in PanIN3 and adenocarcinoma tissues. COX-2 activity was significantly elevated in hamster and human pancreatic cancers compared to pair-matched normal pancreas. Furthermore, hamster pancreatic tumor engraftment/formation in the PC-1 hamster pancreatic cancer model was reduced 4.9-fold by oral administration of sulindac. Increased COX-2 expression is an early event in pancreatic carcinogeneses. The BOP-induced hamster carcinogenesis model is a representative model used to study the role of COX-2 in well-differentiated pancreatic tumorigenesis. COX inhibitors may have a role in preventing tumor engraftment/formation.

Enhanced cell cycle progression and down regulation of p21(Cip1/Waf1) by PRL tyrosine phosphatases.

Human PRL-1, PRL-2, and PRL-3 tyrosine phosphatases induce the malignant transformation of epithelial cells. We tested the hypothesis that the oncogenic effects of PRL occur by increasing cellular proliferation. Cells stably transfected with PRL-1 or PRL-2 exhibited 2.7-3.3-fold increases over control cells in the rate of DNA synthesis and the proportion of cells in S-phase, and they progressed more rapidly from G1 into S. In addition, cells overexpressing either PRL-1 or PRL-2 exhibited enhanced cyclin-dependent kinase 2 (CDK2) activity and significantly lower p21(Cip1/Waf1) protein levels, and PRL-1 overexpressing cells had higher cyclin A protein levels than control cells. We conclude that PRL phosphatases increase cell proliferation by stimulating progression from G1 into S phase, and this process may be dependent on the down regulation of the cyclin dependent kinase inhibitor p21(Cip1/Waf1).

Effects of the isoprenoids perillyl alcohol and farnesol on apoptosis biomarkers in pancreatic cancer chemoprevention.

Perillyl alcohol, farnesol and geraniol have chemotherapeutic activity toward pancreatic and other cancers. Perillyl alcohol induces apoptosis and increases expression of the proapoptotic protein Bak in cultured pancreatic tumor cells. We tested the hypothesis that farnesol and geraniol would have similar effects. After 48 hours of treatment with farnesol geraniol or perillyl alcohol, human BxPC3 pancreatic cancer cells exhibited a 3 to 10-fold increase in apoptosis and higher Bak expression than the controls. We then tested the hypotheses that perillyl alcohol and farnesol would have chemopreventive activity toward pancreatic cancer and would increase Bak expression and apoptosis in vivo. Hamster pancreatic cancer was initiated at time 0 with N-nitrosobis(2-oxopropyl)amine. Animals were fed control, 2% (w/w) perillyl alcohol, or 1% (w/w) farnesol diets from weeks 5-42. Pancreatic carcinoma incidence was decreased by perillyl alcohol and farnesol. Hyperplastic pancreatic ductal neoplasms from perillyl alcohol and farnesol-treated animals had higher Bak protein expression (p < 0.05), and somewhat higher apoptotic rates, diminished expression of the antiapoptotic protein BCL-XL, and lower rates of DNA synthesis than the controls.