Li H Y, Kotaka M, Kostin S, Lee S M, Kok L D, Chan K K, Tsui S K, Schaper J, Zimmermann R, Lee C Y, Fung K P, Waye M M
Department of Biochemistry, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
Cell Motil Cytoskeleton. 2001 Jan;48(1):11-23. doi: 10.1002/1097-0169(200101)48:1<11::AID-CM2>3.0.CO;2-I.
LIM domain proteins are found to be important regulators in cell growth, cell fate determination, cell differentiation, and remodeling of the cell cytoskeleton. Human Four-and-a-half LIM-only protein 2 (FHL2) is expressed predominantly in human heart and is only slightly expressed in skeletal muscle. Since FHL2 is an abundant protein in human heart, it may play an important role in the regulation of cell differentiation and myofibrillogenesis of heart at defined subcellular compartment. Therefore, we hypothesized that FHL2 act as a multi-functional protein by the specific arrangement of the LIM domains of FHL2 and that one of the LIM domains of FHL2 can function as an anchor and localizes it into a specific subcellular compartment in a cell type specific manner to regulate myofibrillogenesis. From our results, we observed that FHL2 is localized at the focal adhesions of the C2C12, H9C2 myoblast as well as a nonmyogenic cell line, HepG2 cells. Colocalization of vinculin-CFP and FHL2-GFP at focal adhesions was also observed in cell lines. Site-directed mutagenesis, in turn, suggested that the second LIM domain-LIM2 is essential for its specific localization to focal adhesions. Moreover, FHL2 was observed along with F-actin and focal adhesion of C2C12 and H9C2 myotubes. Finally, we believe that FHL2 moves from focal adhesions and then stays at the Z-discs of terminally differentiated heart muscle.
人们发现，LIM结构域蛋白是细胞生长、细胞命运决定、细胞分化以及细胞骨架重塑过程中的重要调节因子。人四半LIM-only蛋白2（FHL2）主要在人的心脏中表达，在骨骼肌中仅有少量表达。由于FHL2是人类心脏中一种丰富的蛋白质，它可能在特定亚细胞区室中对心脏的细胞分化和肌原纤维生成的调节中发挥重要作用。因此，我们推测FHL2通过其LIM结构域的特定排列发挥多功能蛋白的作用，并且FHL2的一个LIM结构域可以作为锚定物，以细胞类型特异性的方式将其定位到特定的亚细胞区室中，从而调节肌原纤维生成。从我们的结果来看，我们观察到FHL2定位于C2C12、H9C2成肌细胞以及非肌源性细胞系HepG2细胞的粘着斑。在细胞系中也观察到粘着斑蛋白-CFP和FHL2-GFP在粘着斑处共定位。反过来，定点诱变表明第二个LIM结构域-LIM2对于其在粘着斑的特异性定位至关重要。此外，在C2C12和H9C2肌管的F-肌动蛋白和粘着斑处也观察到了FHL2。最后，我们认为FHL2从粘着斑移动，然后停留在终末分化心肌的Z盘处。
