Abstract
Expression of the Y-box protein YB-1 is increased in proliferating normal and cancer cells, but its role in cell proliferation and cell cycle progression is unclear. We have identified a cell cycle-dependent relocalization of YB-1 from the cytoplasm to the nucleus at the G1/S phase transition and demonstrate that both the charged zipper and the cold shock domain are involved in regulating this process. Using cell lines that constitutively overexpress YB-1, we show that nuclear accumulation of YB-1 is associated with increased cyclin A and cyclin B1 mRNA and protein expression. We provide evidence that deregulated YB-1 expression is linked to adhesion-independent cell proliferation through the induction of cyclin A. Thus, we have identified YB-1 as a cell cycle stage-specific transcription factor important for cell proliferation.
Highlights
Is induced in T lymphocytes by interleukin 2 stimulation, where it is involved in stabilizing interleukin 2 mRNA [12]
The Intracellular Localization of YB-1 Is Cell Cycle-regulated—It has been previously reported that YB-1 is located predominantly in the perinuclear space of the cytoplasm [26, 27], and that certain cellular stresses like hyperthermia and UV irradiation cause nuclear accumulation of the protein [25, 28]
YB-1 was present in the cytoplasm, whereas it appeared in the nucleus 9 to 10 h after the lovastatin block release
Summary
Is induced in T lymphocytes by interleukin 2 stimulation, where it is involved in stabilizing interleukin 2 mRNA [12]. A deletion of the basic amino acid cluster at the very end of the C-terminal tail of YB-1 was associated with a loss of cell cycle-regulated nuclear accumulation of YB-1, as the GFP/YB-1 fusion protein was located either in the cytoplasm or the nucleus in 50% of the transfected cells (Fig. 2B, c3). A deletion of the adjacent cluster of basic amino acids was associated with a nuclear location of the GFP/YB-1 fusion protein in 100% of the transfected cells (Fig. 2B, c4).
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