Involvement of 14-3-3 proteins in nuclear localization of telomerase

Hiroyuki Seimiya^1,2,3, Hiroko Sawada¹, Yukiko Muramatsu¹, Mayuko Shimizu¹, Kumiko Ohko¹, Kazuhiko Yamane¹, and Takashi Tsuruo^1,4

¹Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, 1-37-1 Kami-Ikebukuro, Toshima-ku, Tokyo 170-8455 and ⁴Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan ²Present address: Skirball Institute of Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, 2nd Floor, New York, NY 10016, USA ³Corresponding author e-mail: seimiya{at}saturn.med.nyu.edu

Abstract: Maintenance of telomeres is implicated in chromosome stabilization and cell immortalization. Telomerase, which catalyzes de novo synthesis of telomeres, is activated in germ cells and most cancers. Telomerase activity is regulated by gene expression for its catalytic subunit, TERT, whereas several lines of evidence have suggested a post-translational regulation of telomerase activity. Here we identify the 14-3-3 signaling proteins as human TERT (hTERT)-binding partners. A dominant-negative 14-3-3 redistributed hTERT, which was normally predominant in the nucleus, into the cytoplasm. Consistent with this observation, hTERT-3A, a mutant that could not bind 14-3-3, was localized into the cytoplasm. Leptomycin B, an inhibitor of CRM1/exportin 1-mediated nuclear export, or disruption of a nuclear export signal (NES)-like motif located just upstream of the 14-3-3 binding site in hTERT impaired the cytoplasmic localization of hTERT. Compared with wild-type hTERT, hTERT-3A increased its association with CRM1. 14-3-3 binding was not required for telomerase activity either in vitro or in cell extracts. These observations suggest that 14-3-3 enhances nuclear localization of TERT by inhibiting the CRM1 binding to the TERT NES-like motif.

Key Words: Keywords: hTERT/nuclear localization/telomerase/14-3-3