Impaired p14^ARF and MDM2 Nuclecytoplasmic Shuttling in Uveal Melanoma

Abstract

Purpose : It is estimated that 90% of cancer-related deaths are due to metastases and not the primary tumor. The development of metastases is correlated with poor prognosis and there are few effective anti-metastatic treatments. The TP53-MDM2 signaling pathway is considered to play a central role in the control of tumors and metastases. Emerging evidence shows MDM2 gene amplification is detected in 40-80% of high-grade tumors. While a correlation exists between MDM2 levels and metastases, studies addressing the subcellular localization of MDM2 and p14^ARF, an upstream regulator of MDM2, in metastatic versus primary tumors are scarce. In this study we investigated the subcellular localization of phosphorylated MDM2, p53, and p14^ARF in primary and metastatic UM cells.

Methods : We performed immunohistochemical studies using antibodies specific for p-p53, p-MDM2, and p14^ARF in vitro in primary and metastatic UM cell lines and ex vivo (post mortem) in samples from the metastatic liver of a UM patient.

Results : Comparison of UM cell lines derived from primary or metastatic tumors revealed nuclear localization of p-MDM2 along with increased immunoreactivity in metastatic UM. In contrast, p-p53 was abundant both in the cytoplasm and the nucleus of primary tumor-derived UM cells. The MDM2 regulator, p14^ARF, was localized to the cytoplasm of UM cells.

Conclusions : Our investigation revealed that p-MDM2 is almost exclusively localized to the nucleoplasm of metastatic cells, while p-p53 is in both the cytoplasm and nucleoplasm of cells under steady-state conditions. In addition, we demonstrate that p14^ARF, an upstream regulator of MDM2 is localized to the cytoplasm of UM cells. Collectively, our work suggests defective nucleocytoplasmic transport in metastatic UM cells, which is an essential physiological process likely to have clinical implications in sensitivity to chemotherapeutics and small molecule inhibitors.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.