Gupta Anandarup, Lee Beth S, Khadeer Mohammed A, Tang Zhihui, Chellaiah Meenakshi, Abu-Amer Yousef, Goldknopf Joshua, Hruska Keith A
Department of Oral and Craniofacial Biological Sciences, University of Maryland, Baltimore, Maryland 21201-1586, USA.
J Bone Miner Res. 2003 Apr;18(4):669-85. doi: 10.1359/jbmr.2003.18.4.669.
Leupaxin is a cytoskeleton adaptor protein that was first identified in human macrophages and was found to share homology with the focal adhesion protein, paxillin. Leupaxin possesses several protein-binding domains that have been implicated in targeting proteins such as focal adhesion kinase (pp125FAK) to focal adhesions. Leupaxin can be detected in monocytes and osteoclasts, both cells of hematopoietic origin. We have identified leupaxin to be a component of the osteoclast podosomal signaling complex. We have found that leupaxin in murine osteoclasts is associated with both PYK2 and pp125FAK in the osteoclast. Treatment of osteoclasts with TNF-alpha and soluble osteopontin were found to stimulate tyrosine phosphorylation of both leupaxin and leupaxin-associated PYK2. Leupaxin was found to co-immunoprecipitate with the protein tyrosine phosphatase PTP-PEST. The cellular distribution of leupaxin, PYK2, and protein tyrosine phosphorylation-PEST co-localized at or near the osteoclast podosomal complex. Leupaxin was also found to associate with the ARF-GTPase-activating protein, paxillin kinase linker p95PKL, thereby providing a link to regulators of cytoskeletal dynamics in the osteoclast. Overexpression of leupaxin by transduction into osteoclasts evoked numerous cytoplasmic projections at the leading edge of the cell, resembling a motile phenotype. Finally, in vitro inhibition of leupaxin expression in the osteoclast led to a decrease in resorptive capacity. Our data suggest that leupaxin may be a critical nucleating component of the osteoclast podosomal signaling complex.
白细胞盘状蛋白是一种细胞骨架衔接蛋白，最初在人类巨噬细胞中被鉴定出来，发现它与粘着斑蛋白桩蛋白具有同源性。白细胞盘状蛋白拥有几个蛋白质结合结构域，这些结构域与将诸如粘着斑激酶（pp125FAK）等蛋白质靶向粘着斑有关。在单核细胞和破骨细胞中都能检测到白细胞盘状蛋白，这两种细胞均起源于造血系统。我们已经确定白细胞盘状蛋白是破骨细胞足体信号复合物的一个组成部分。我们发现，小鼠破骨细胞中的白细胞盘状蛋白与破骨细胞中的PYK2和pp125FAK都有关联。用肿瘤坏死因子-α和可溶性骨桥蛋白处理破骨细胞，发现会刺激白细胞盘状蛋白和与白细胞盘状蛋白相关的PYK2的酪氨酸磷酸化。发现白细胞盘状蛋白与蛋白酪氨酸磷酸酶PTP-PEST共同免疫沉淀。白细胞盘状蛋白、PYK2和蛋白酪氨酸磷酸化-PEST的细胞分布在破骨细胞足体复合物处或其附近共定位。还发现白细胞盘状蛋白与ARF-GTP酶激活蛋白桩蛋白激酶连接蛋白p95PKL相关联，从而为破骨细胞中细胞骨架动力学的调节因子提供了一个联系。通过转导将白细胞盘状蛋白过表达至破骨细胞中，会在细胞前缘诱发大量细胞质突起，类似于运动表型。最后，在体外抑制破骨细胞中白细胞盘状蛋白的表达会导致吸收能力下降。我们的数据表明，白细胞盘状蛋白可能是破骨细胞足体信号复合物的关键成核成分。
