Research

PRIMA-1^MET induces nucleolar translocation of Epstein-Barr virus-encoded EBNA-5 protein

György Stuber¹ , Emilie Flaberg^1,2,3 , Gabor Petranyi^1,2,4 , Rita Ötvös¹ , Nina Rökaeus⁵ , Elena Kashuba^1,3 , Klas G Wiman⁵ , George Klein¹ and Laszlo Szekely^1,2,3

¹  Department of Microbiology, Tumor and Cell Biology (MTC), Karolinska Institute, S-171 77 Stockholm, Sweden

²  Karolinska Institute Visualization Core Facility (KIVIF), Karolinska Institute, S-171 77 Stockholm, Sweden

³  Center for Integrative Recognition in the Immune System (IRIS), Karolinska Institute, S-171 77 Stockholm, Sweden

⁴  Swedish Center for Disease Control (SMI), S-171 82 Solna, Sweden

⁵  Deptarment of Oncology-Pathology, Cancer Center Karolinska (CCK), Karolinska Institute, S-171 76 Stockholm, Sweden

author email corresponding author email

Molecular Cancer 2009, 8:23doi:10.1186/1476-4598-8-23

Published:	26 March 2009

Abstract

The low molecular weight compound, PRIMA-1^MET restores the transcriptional transactivation function of certain p53 mutants in tumor cells. We have previously shown that PRIMA-1^MET induces nucleolar translocation of p53, PML, CBP and Hsp70. The Epstein-Barr virus encoded, latency associated antigen EBNA-5 (also known as EBNA-LP) is required for the efficient transformation of human B lymphocytes by EBV. EBNA-5 associates with p53-hMDM2-p14ARF complexes. EBNA-5 is a nuclear protein that translocates to the nucleolus upon heat shock or inhibition of proteasomes along with p53, hMDM2, Hsp70, PML and proteasome subunits. Here we show that PRIMA-1^MET induces the nucleolar translocation of EBNA-5 in EBV transformed B lymphoblasts and in transfected tumor cells. The PRIMA-1^MET induced translocation of EBNA-5 is not dependent on the presence of mutant p53. It also occurs in p53 null cells or in cells that express wild type p53. Both the native and the EGFP or DSRed conjugated EBNA-5 respond to PRIMA-1^MET treatment in the same way. Image analysis of DSRed-EBNA-5 expressing cells, using confocal fluorescence time-lapse microscopy showed that the nucleolar translocation requires several hours to complete. FRAP (fluorescence recovery after photobleaching) and FLIP (fluorescence loss in photobleaching) measurements on live cells showed that the nucleolar translocation was accompanied by the formation of EBNA-5 aggregates. The process is reversible since the aggregates are dissolved upon removal of PRIMA-1^MET. Our results suggest that mutant p53 is not the sole target of PRIMA-1^MET. We propose that PRIMA-1^MET may reversibly inhibit cellular chaperons that prevent the aggregation of misfolded proteins, and that EBNA-5 may serve as a surrogate drug target for elucidating the precise molecular action of PRIMA-1^MET.