Ebner Hannes L, Blatzer Michael, Nawaz Muhammad, Krumschnabel Gerhard
Institut für Zoologie und Limnologie, and Center of Molecular Biosciences, Leopold Franzens Universität Innsbruck, Innsbruck, Austria.
J Exp Biol. 2007 Mar;210(Pt 6):1036-45. doi: 10.1242/jeb.02719.
The mitogen-activated protein kinase ERK is an important signalling molecule involved in the control of cell proliferation, differentiation and cell death, targeting molecules at the cell membrane, in the cytosol, and in the nucleus. This study investigated the activation pattern and subcellular distribution of ERK in liver and gill cells of rainbow trout upon hypo-osmotic shock, addition of epidermal growth factor (EGF) and copper treatment. It further set out to characterize the hypothetical role of nuclear-export signal (NES)-dependent relocation of ERK after nuclear entry and the potential involvement of the ERK activator MEK. Although, in primary hepatocytes, ERK was activated in all conditions in a stimulus-specific manner, it did not accumulate in the nucleus, irrespective of the absence or presence of the inhibitor of NES-dependent export leptomycin B (LB). Similarly, in trout hepatoma cells, where pERK levels increased upon osmotic and mitotic stimulation, but not after toxic insult, no significant nuclear translocation was observed. In a gill cell line, levels of pERK increased after osmotic and mitotic stimulation and showed a decrease during incubation with a toxicant. Again, none of these conditions triggered nuclear accumulation of pERK in the gill cells in the absence of LB, but in contrast to the observation in liver cells, both osmotic and mitotic stimulation caused nuclear accumulation in the presence of the inhibitor. The ERK activator MEK, which possesses a NES-sequence, was apparently not involved in nuclear export, as it did not seem to enter the nucleus. Altogether, ERK is activated in trout cells in a stimulus- and cell type-specific manner, and our data suggest that it acutely acts primarily on cytoplasmic or membrane-situated targets in liver cells, whereas it presumably triggers rapid transcriptional activities in gill cells.
丝裂原活化蛋白激酶ERK是一种重要的信号分子，参与细胞增殖、分化和细胞死亡的调控，其作用靶点包括细胞膜、细胞质和细胞核中的分子。本研究调查了虹鳟鱼肝脏和鳃细胞在低渗休克、添加表皮生长因子（EGF）和铜处理后ERK的激活模式和亚细胞分布。研究还进一步探讨了ERK进入细胞核后依赖核输出信号（NES）重新定位的假设作用以及ERK激活剂MEK的潜在参与情况。虽然在原代肝细胞中，ERK在所有条件下均以刺激特异性方式被激活，但无论是否存在NES依赖输出抑制剂雷帕霉素B（LB），它都不会在细胞核中积累。同样，在鳟鱼肝癌细胞中，pERK水平在渗透和有丝分裂刺激后升高，但在毒性损伤后未升高，未观察到明显的核转位。在一种鳃细胞系中，pERK水平在渗透和有丝分裂刺激后升高，在与毒物孵育期间降低。同样，在没有LB的情况下，这些条件均未触发鳃细胞中pERK的核积累，但与肝细胞中的观察结果相反，在抑制剂存在的情况下，渗透和有丝分裂刺激均导致核积累。具有NES序列的ERK激活剂MEK显然不参与核输出，因为它似乎没有进入细胞核。总之，ERK在鳟鱼细胞中以刺激和细胞类型特异性方式被激活，我们的数据表明，它在肝细胞中主要急性作用于细胞质或膜上的靶点，而在鳃细胞中可能触发快速的转录活性。
