Sahu Surasri Nandan, Khadeer Mohammed Abdul, Robertson Brian W, Núñez Stephanie M, Bai Guang, Gupta Anandarup
Department of Biomedical Sciences, 4G-29, Dental School, University of Maryland-Baltimore, 666 West Baltimore St., Baltimore, MD 21201, USA.
Am J Physiol Cell Physiol. 2007 Jan;292(1):C581-90. doi: 10.1152/ajpcell.00636.2005. Epub 2006 Aug 16.
Leupaxin (LPXN), which belongs to the paxillin extended family of adaptor proteins, was previously identified as a component of the sealing zone in osteoclasts. LPXN was found to associate with several podosomal proteins, such as the protein tyrosine kinase Pyk2, the protein-tyrosine phosphatase-PEST (PTP-PEST), actin-binding proteins, and regulators of actin cytoskeletal reorganization. It was previously demonstrated that inhibition of LPXN expression resulted in reduced osteoclast-mediated resorption. In the current study, overexpression of LPXN in murine osteoclasts resulted in both enhanced resorptive activity and cell adhesion, as assessed by in vitro resorption assays. The overexpression of LPXN resulted in an increased association of Pyk2 with LPXN. In an attempt to determine an additional biochemical basis for the observed phenomenon in increased osteoclast activity, a coimmunoprecipitation screen for additional binding partners revealed that Src, a protein tyrosine kinase that is critical to both podosome formation and osteoclast function, was also associated with LPXN. After exposure to the pro-inflammatory and osteoclastogenic cytokine TNF-alpha, there was an increase in the level of Src that coimmunoprecipitated with LPXN. Our data indicate that association of the scaffold protein LPXN with Src adds further complexity to the organization of the podosomal signaling complex in osteoclasts.
白细胞共同抗原相关蛋白（LPXN）属于衔接蛋白的桩蛋白扩展家族，先前被鉴定为破骨细胞封闭带的一个组成部分。研究发现，LPXN与几种足体蛋白相关，如蛋白酪氨酸激酶Pyk2、蛋白酪氨酸磷酸酶-PEST（PTP-PEST）、肌动蛋白结合蛋白以及肌动蛋白细胞骨架重组调节因子。先前的研究表明，抑制LPXN表达会导致破骨细胞介导的吸收减少。在本研究中，通过体外吸收试验评估，LPXN在小鼠破骨细胞中的过表达导致吸收活性和细胞黏附增强。LPXN的过表达导致Pyk2与LPXN的结合增加。为了确定破骨细胞活性增加这一现象的另一个生化基础，对其他结合伙伴进行的免疫共沉淀筛选显示，Src（一种对足体形成和破骨细胞功能都至关重要的蛋白酪氨酸激酶）也与LPXN相关。暴露于促炎和破骨细胞生成细胞因子肿瘤坏死因子-α（TNF-α）后，与LPXN免疫共沉淀的Src水平增加。我们的数据表明，支架蛋白LPXN与Src的结合使破骨细胞中足体信号复合物的组织更加复杂。
