Abstract
Telomeric repeat-binding factor 2 (TRF2) was reported to localize in the nucleolus of human cells in a cell cycle-dependent manner; however, the underlying mechanism remains unclear. Here, we found that nucleolar and coiled-body phosphoprotein 1 (NOLC1) interacted with TRF2 and mediated the shuttling of TRF2 between the nucleolus and nucleus in human 293T and HepG2 cells. Ablation of NOLC1 expression increased the number of nuclear TRF2 foci and decreased the nucleolar level of TRF2. Conversely, NOLC1 overexpression promoted the nucleolar accumulation of TRF2. NOLC1 overexpression also increased the number of 53BP1 foci and induced the DNA damage response. In addition, co-expression of TRF2 rescued NOLC1 overexpression-induced cell cycle arrest and apoptosis.
Highlights
To explore the potential proteins that interact with Nucleolar and coiled-body phosphoprotein 1 (NOLC1), exogenous Flag-NOLC1 was pulled down and NOLC1-associated proteins were identified by mass spectrometry (MS) analysis (Figures 1a and b)
Telomeric repeat-binding factor 2 (TRF2) binds to telomeres and functions in telomere protection,[11] raising the possibility that NOLC1 participates in telomere-associated biological regulation
Correspondence: T Tong Received 30 March 2017; revised 24 May 2017; accepted 3 June 2017; Edited by N Barlev results, when 293T cells were co-transfected with Flag-NOLC1 and GFP-TRF2, TRF2 was detected in the immunoprecipitate obtained using an anti-Flag antibody (Figure 1c)
Summary
The regulation of gene function involves a series of processes including protein production, modification, and degradation,[1,2] in which the regulation of protein distribution in different subcellular structures is one of an important way.[3,4,5] The nucleolus is a eukaryotic subnuclear organelle that is responsible for ribosomal RNA (rRNA) transcription, processing, and modification and ribosome assembly.[6,7,8] Accumulating evidence has linked the nucleolus with many other processes besides rRNA metabolism, leading to the concept that it is a plurifunctional organelle.[9,10,11,12,13,14]Many studies show that the functions of some proteins are regulated via control of their nucleolar retention. We failed to visualize TRF2 in the nucleolus of human Hela cells using the same antibody; instead, discrete foci were stained in the nucleoplasm, which probably correspond to telomeres (Figure 2). Western blotting indicated that knockdown or overexpression of NOLC1 did not significantly affect expression of TRF2 (Figures 3a and b). After NOLC1 knockdown in 293T cells, TRF2 was released from the nucleolus into the nucleoplasm.
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