Translocation of a human focal adhesion LIM-only protein, FHL2, during myofibrillogenesis and identification of LIM2 as the principal determinants ofFHL2 focal adhesion localization

LIM domain proteins are found to be important regulators in cell growth, ce ll fate determination, cell differentiation, and remodeling of the cell cyt oskeleton. Human Four-and-a-half LIM-only protein 2 (FHL2) is expressed pre dominantly in human heart and is only slightly expressed in skeletal muscle . Since FHL2 is an abundant protein in human heart, it may play an importan t role in the regulation of cell differentiation and myofibrillogenesis of heart at defined subcellular compartment. Therefore, we hypothesized that F HL2 act as a multi-functional protein by the specific arrangement of the LI M domains of FHL2 and that one of the LIM domains of FHL2 can function as a n 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 m yoblast as well as a nonmyogenic cell Line, HepG2 cells. Colocalization of vinculin-CFP and FHL2-GFP at focal adhesions was also observed in cell line s. Site-directed mutagenesis, in turn, suggested that the second LIM domain -LIM2 is essential for its specific localization to focal adhesions. Moreov er, FHL2 was observed along with F-actin and focal adhesion of C2C12 and H9 C2 myotubes. Finally, we believe that FHL2 moves from focal adhesions and t hen stays at the Z-discs of terminally differentiated heart muscle. Cell Mo til. Cytoskeleton 48:11-23, 2001. (C) 2001 Wiley-Liss, Inc.