de Graaf Petra, Klapisz Elsa E, Schulz Thomas K F, Cremers Alfons F M, Verkleij Arie J, van Bergen en Henegouwen Paul M P
Molecular Cell Biology, Institute of Biomembranes, Universiteit Utrecht, The Netherlands.
J Cell Sci. 2002 Apr 15;115(Pt 8):1769-75. doi: 10.1242/jcs.115.8.1769.
Whereas most phosphatidylinositol 4-kinase (PtdIns 4-kinase) activity is localized in the cytoplasm, PtdIns 4-kinase activity has also been detected in membrane-depleted nuclei of rat liver and mouse NIH 3T3 cells. Here we have characterized the PtdIns 4-kinase that is present in nuclei from NIH 3T3 cells. Both type II and type III PtdIns 4-kinase activity were observed in the detergent-insoluble fraction of NIH 3T3 cells. Dissection of this fraction into cytoplasmic actin filaments and nuclear lamina-pore complexes revealed that the actin filament fraction contains solely type II PtdIns 4-kinase, whereas lamina-pore complexes contain type III PtdIns 4-kinase activity. Using specific antibodies, the nuclear PtdIns 4-kinase was identified as PtdIns 4-kinase beta. Inhibition of nuclear export by leptomycin B resulted in an accumulation of PtdIns 4-kinase beta in the nucleus. These data demonstrate that PtdIns 4-kinase beta is present in the nuclei of NIH 3T3 fibroblasts, suggesting a specific function for this kinase in nuclear processes.
虽然大多数磷脂酰肌醇4激酶（PtdIns 4激酶）活性定位于细胞质中，但在大鼠肝脏和小鼠NIH 3T3细胞的膜缺失细胞核中也检测到了PtdIns 4激酶活性。在此，我们对NIH 3T3细胞核中存在的PtdIns 4激酶进行了表征。在NIH 3T3细胞的去污剂不溶性组分中观察到了II型和III型PtdIns 4激酶活性。将该组分分离为细胞质肌动蛋白丝和核纤层-孔复合物，结果显示肌动蛋白丝组分仅含有II型PtdIns 4激酶，而核纤层-孔复合物含有III型PtdIns 4激酶活性。使用特异性抗体，将核PtdIns 4激酶鉴定为PtdIns 4激酶β。雷帕霉素B对核输出的抑制导致PtdIns 4激酶β在细胞核中积累。这些数据表明PtdIns 4激酶β存在于NIH 3T3成纤维细胞的细胞核中，提示该激酶在核过程中具有特定功能。
