Institute of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany.
Institute of Biochemistry and Signal Transduction, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany.
Cell Signal. 2018 Sep;49:87-94. doi: 10.1016/j.cellsig.2018.05.006. Epub 2018 May 28.
The inositol 5-phosphatase SHIP1 acts as negative regulator of intracellular signaling in myeloid cells and is a tumor suppressor in myeloid leukemogenesis. After relocalization from the cytoplasm to the plasma membrane SHIP1 terminates PI3-kinase mediated signaling processes. Furthermore, SHIP1 is also found in distinct puncta in the cell nucleus and nuclear SHIP1 has a pro-proliferative function. Here we report the identification of five nuclear export signals (NESs) which regulate together with the two known nuclear localization signals (NLSs) the nucleocytoplasmic shuttling of SHIP1. Mutation of NLSs reduced the nuclear import and mutation of NESs decreased the nuclear export of SHIP1 in the acute myeloid leukemia (AML) cell line UKE-1. Interestingly, four SHIP1 mutants (K210R, N508D, V684E, Q1153L) derived from AML patients showed a nuclear accumulation after expression in UKE-1 cells. In addition, overexpression of the AML patient-derived mutation N508D caused an increased proliferation rate of UKE-1 cells in comparison to wild type SHIP1. Furthermore, we identified serine and tyrosine phosphorylation as a molecular mechanism for the regulation of nucleocytoplasmic shuttling of SHIP1 where tyrosine phosphorylation of distinct residues i.e. Y864, Y914, Y1021 reduces nuclear localization, whereas serine phosphorylation at S933 enhances nuclear localization of SHIP1. In summary, our data further implicate nuclear SHIP1 in cellular signaling and suggest that enhanced accumulation of SHIP1 mutants in the nucleus may be a contributory factor of abnormally high proliferation of AML cells.
肌醇 5-磷酸酶 SHIP1 作为骨髓细胞内信号的负调控因子，是骨髓白血病发生过程中的肿瘤抑制因子。SHIP1 从细胞质重新定位到质膜后，终止 PI3-激酶介导的信号转导过程。此外，SHIP1 还存在于细胞核中的不同点状结构中，核内 SHIP1 具有促增殖功能。本研究报告了五个核输出信号（NES）的鉴定，这些信号与两个已知的核定位信号（NLS）一起调节 SHIP1 的核质穿梭。NLS 突变减少了核内输入，NES 突变减少了 UKE-1 急性髓系白血病（AML）细胞系中的核输出。有趣的是，从 AML 患者中获得的四个 SHIP1 突变体（K210R、N508D、V684E、Q1153L）在 UKE-1 细胞中表达后出现核内积累。此外，与野生型 SHIP1 相比，AML 患者衍生的突变体 N508D 的过表达导致 UKE-1 细胞增殖率增加。此外，我们确定丝氨酸和酪氨酸磷酸化是调节 SHIP1 核质穿梭的分子机制，即特定残基（即 Y864、Y914、Y1021）的酪氨酸磷酸化减少核定位，而 S933 处的丝氨酸磷酸化增强 SHIP1 的核定位。总之，我们的数据进一步表明核内 SHIP1 参与细胞信号转导，并提示 SHIP1 突变体在核内的积累增加可能是 AML 细胞异常高增殖的一个促成因素。
