Department of Biological Sciences, Wayne State University, Detroit, MI 48202, USA.
Biochem Biophys Res Commun. 2011 Jun 24;410(1):91-6. doi: 10.1016/j.bbrc.2011.05.112. Epub 2011 May 27.
Cell adhesion and migration are important events that occur during embryonic development, immune surveillance, wound healing and in tumor metastasis. It is a multi-step process that involves both mechanical and biochemical signaling that results in cell protrusion, adhesion, contraction and retraction. Each of these events generates mechanical forces into the environment measured as traction forces. We have previously found that the calpain small subunit, Calpain 4, is required for normal traction forces, and that this mechanism is independent of the catalytic activities of the holoenzymes that are formed between Calpain 4 and each of the proteolytic heavy chains of Calpain 1 and 2. To define a potential mechanism for the Calpain 4 regulation of traction force, we have evaluated the levels of tyrosine phosphorylation, a hallmark of force dependent signaling within focal adhesions. Using 2D gel electrophoresis we compared tyrosine phosphorylation profiles of Calpain 4 deficient mouse embryonic fibroblasts (MEFs) to the levels in wildtype MEFs and MEF's deficient in the large catalytic subunits, Capn1 and Capn2. Of particular interest, was the identification of Galectin-3, a galactose binding protein known to interact with integrins. Galectin-3 has previously been shown to regulate cell adhesion and migration in both normal and tumor cells; however its full mechanism remains elusive. We have found that Calpain 4 is essential for the tyrosine phosphorylation of galectin-3, and its ultimate secretion from the cell, and speculate that its secretion interferes with the production of traction forces.
细胞黏附和迁移是胚胎发育、免疫监视、伤口愈合和肿瘤转移过程中发生的重要事件。这是一个多步骤的过程，涉及机械和生化信号，导致细胞突起、黏附、收缩和回缩。这些事件中的每一个都会产生机械力进入环境，这些力被测量为牵引力。我们之前发现，钙蛋白酶小亚基 Calpain 4 是正常牵引力所必需的，并且这种机制独立于形成 Calpain 4 和 Calpain 1 和 2 的每个蛋白水解重链之间的全酶的催化活性。为了定义 Calpain 4 调节牵引力的潜在机制，我们评估了酪氨酸磷酸化水平，这是粘着斑内力依赖信号的标志。使用二维凝胶电泳，我们将 Calpain 4 缺陷型小鼠胚胎成纤维细胞 (MEF) 的酪氨酸磷酸化谱与野生型 MEF 和缺乏大催化亚基 Capn1 和 Capn2 的 MEF 的水平进行了比较。特别有趣的是鉴定了半乳糖结合蛋白 Galectin-3，Galectin-3 已知与整合素相互作用。Galectin-3 先前已被证明可调节正常和肿瘤细胞中的细胞黏附和迁移；然而，其完整的机制仍不清楚。我们发现 Calpain 4 对于半乳糖结合蛋白 Galectin-3 的酪氨酸磷酸化及其最终从细胞中分泌是必需的，并且推测其分泌会干扰牵引力的产生。
