Marti A, Luo Z, Cunningham C, Ohta Y, Hartwig J, Stossel T P, Kyriakis J M, Avruch J
Diabetes Unit and Medical Services, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 021291, USA.
J Biol Chem. 1997 Jan 31;272(5):2620-8. doi: 10.1074/jbc.272.5.2620.
SEK-1, a dual specificity protein kinase that serves as one of the immediate upstream activators of the stress-activated protein kinases (SAPKs), associates specifically with the actin-binding protein, ABP-280, in vitro and in situ. SEK-1 binds to the carboxyl-terminal rod segment of ABP-280, upstream of the ABP carboxyl-terminal dimerization domain. Activation of SEK-1 in situ increases the SEK-1 activity bound to ABP-280 without changing the amount of SEK-1 polypeptide bound. The influence of ABP-280 on SAPK regulation was evaluated in human melanoma cells that lack ABP-280 expression, and in stable transformants of these cells expressing wild type ABP, or an actin-binding but dimerization-deficient mutant ABP (ABPDeltaCT109). ABP-280-deficient cells show an activation of SAPK in response to most stimuli that is comparable to that seen in ABP-280-replete cells; ABP-280-deficient cells, however, fail to show the brisk tumor necrosis factor-alpha (TNF-alpha) activation of SAPK seen in ABP-replete cells and have an 80% reduction in SAPK activation by lysophosphatidic acid. Expression of the dimerization-deficient mutant ABP-280 fails to correct the defective SAPK response to lysophosphatidic acid, but essentially normalizes the TNF-alpha activation of SAPK. Thus, a lack of ABP-280 in melanoma cells causes a defect in the regulation of SAPK that is selective for TNF-alpha and is attributable to the lack of ABP-280 polypeptide itself rather than to the disordered actin cytoskeleton that results therefrom. ABP-280 participates in TNF-alpha signal transduction to SAPKs, in part through the binding of SEK-1.
SEK-1是一种双特异性蛋白激酶，作为应激激活蛋白激酶（SAPK）的直接上游激活剂之一，在体外和原位与肌动蛋白结合蛋白ABP-280特异性结合。SEK-1与ABP-280的羧基末端杆状片段结合，位于ABP羧基末端二聚化结构域的上游。原位激活SEK-1可增加与ABP-280结合的SEK-1活性，而不改变结合的SEK-1多肽的量。在缺乏ABP-280表达的人黑色素瘤细胞以及表达野生型ABP或肌动蛋白结合但二聚化缺陷突变体ABP（ABPDeltaCT109）的这些细胞的稳定转化体中，评估了ABP-280对SAPK调节的影响。缺乏ABP-280的细胞在对大多数刺激的反应中显示出与富含ABP-280的细胞相当的SAPK激活；然而，缺乏ABP-280的细胞未能显示出富含ABP的细胞中所见的肿瘤坏死因子-α（TNF-α）对SAPK的快速激活，并且溶血磷脂酸对SAPK的激活降低了80%。二聚化缺陷突变体ABP-280的表达未能纠正对溶血磷脂酸的缺陷性SAPK反应，但基本上使SAPK的TNF-α激活正常化。因此，黑色素瘤细胞中缺乏ABP-280会导致SAPK调节缺陷，该缺陷对TNF-α具有选择性，并且归因于ABP-280多肽本身的缺乏，而不是由此导致的肌动蛋白细胞骨架紊乱。ABP-280部分通过SEK-1的结合参与TNF-α向SAPK的信号转导。
