Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY, USA.
Cell Adh Migr. 2010 Oct-Dec;4(4):527-40. doi: 10.4161/cam.4.4.12399.
Focal adhesion (FA) formation is induced by extracellular matrix-stimulated integrin clustering and activation of receptors for diffusible factors. Leupaxin (LPXN) is a member of the paxillin family of FA proteins expressed in many cancer cell lines. We found activation of gastrin-releasing peptide receptor (GRPr) by bombesin (BN) stimulated LPXN translocation from cytoplasm to FAs. Using mutagenesis, we identified LIM3 as the primary FA targeting domain for LPXN and showed BN-induced LPXN tyrosine phosphorylation on residues 22, 62 and 72. A LIM3 point mutant of LPXN failed to target to FAs and had no BN-stimulated tyrosine phosphorylation. Conversely, a non-phosphorylatable mutant (Y22/62/72F) translocated to FAs after BN addition. Stimulation of FA formation using vinblastine also induced LPXN translocation and tyrosine phosphorylation. Therefore, dynamic LPXN tyrosine phosphorylation requires translocation to FAs. LPXN and paxillin had opposite roles in adhesion to collagen I (CNI) in MDA-MB-231 breast cancer cells. LPXN siRNA stimulated whereas paxillin siRNA inhibited cell adhesion. Knockdown of both LPXN and paxillin behaved similarly to paxillin knockdown alone, suggesting LPXN’s function in adhesion might depend on paxillin. Additionally, LPXN regulated cell spreading on CNI but not on fibronectin whereas paxillin knockdown suppressed spreading on both substrates. These results demonstrate that although LPXN and paxillin’s FA targeting and tyrosine phosphorylation are similar, each protein has distinct functions.
焦点黏附(FA)的形成是由细胞外基质刺激整合素聚集和扩散因子受体的激活诱导的。Leupaxin(LPXN)是一种黏附斑蛋白家族的成员,在许多癌细胞系中表达。我们发现,蛙皮素(BN)刺激胃泌素释放肽受体(GRPr)的激活,导致 LPXN 从细胞质向 FA 的易位。通过突变,我们确定 LIM3 是 LPXN 的主要 FA 靶向结构域,并显示 BN 诱导的 LPXN 酪氨酸残基 22、62 和 72 的磷酸化。LPXN 的 LIM3 点突变体未能靶向 FA,并且没有 BN 刺激的酪氨酸磷酸化。相反,非磷酸化突变体(Y22/62/72F)在 BN 加入后易位到 FA。长春花碱诱导 FA 形成也诱导 LPXN 易位和酪氨酸磷酸化。因此,LPXN 酪氨酸的动态磷酸化需要易位到 FA。在 MDA-MB-231 乳腺癌细胞中,LPXN 和 paxillin 在黏附于胶原 I(CNI)方面发挥相反的作用。LPXN siRNA 刺激而 paxillin siRNA 抑制细胞黏附。LPXN 和 paxillin 的敲低与单独敲低 paxillin 相似,表明 LPXN 在黏附中的功能可能依赖于 paxillin。此外,LPXN 调节细胞在 CNI 上的铺展,但不调节在纤维连接蛋白上的铺展,而 paxillin 敲低抑制了在这两种基质上的铺展。这些结果表明,尽管 LPXN 和 paxillin 的 FA 靶向和酪氨酸磷酸化相似,但每种蛋白都具有独特的功能。