A role for RAD54B in homologous recombination in human cells.

In human somatic cells, homologous recombination is a rare event. To facilitate the targeted modification of the genome for research and gene therapy applications, efforts should be directed toward understanding the molecular mechanisms of homologous recombination in human cells. Although human genes homologous to members of the RAD52 epistasis group in yeast have been identified, no genes have been demonstrated to play a role in homologous recombination in human cells. Here, we report that RAD54B plays a critical role in targeted integration in human cells. Inactivation of RAD54B in a colon cancer cell line resulted in severe reduction of targeted integration frequency. Sensitivity to DNA-damaging agents and sister-chromatid exchange were not affected in RAD54B-deficient cells. Parts of these phenotypes were similar to those of Saccharomyces cerevisiae tid1/rdh54 mutants, suggesting that RAD54B may be a human homolog of TID1/RDH54. In yeast, TID1/RDH54 acts in the recombinational repair pathway via roles partially overlapping those of RAD54. Our findings provide the first genetic evidence that the mitotic recombination pathway is functionally conserved from yeast to humans.     

Interleukin 6 promotes epithelial migration by a fibronectin-dependent mechanism.

We investigated the effect of interleukin 6 (IL-6) on the migration of rabbit corneal epithelium in vitro and on the attachment of dissociated corneal epithelial cells to a fibronectin matrix. When corneal blocks were cultured with IL-6 for 24 hours, the length of the path of epithelial migration over exposed corneal stroma increased significantly (p less than 0.005 at the concentration of 10 ng/ml) in proportion to the concentrations of IL-6 (0.1-10.0 ng/ml). The addition of antiserum against fibronectin or of GRGDSP abolished the stimulatory effect of IL-6 on epithelial migration. When corneal epithelial cells were cultured with various concentrations of IL-6, suspended, and plated on wells coated with fibronectin (10 micrograms/ml), the number of cells attached to the wells increased in a dose-dependent manner. The presence of antibody against fibronectin or of GRGDSP during the attachment assay decreased the number of cells attached to the fibronectin matrix, regardless of the fact that the cells had been cultured with IL-6 or not. IL-6 stimulated the attachment of corneal epithelial cells to collagen type IV and to laminin matrices. However, the presence of GRGDSP did not affect the cell attachment to collagen type IV and to laminin. These findings strongly indicate that IL-6 stimulates epithelial migration in the cornea by a fibronectin-dependent mechanism, presumably the increased expression of fibronectin receptors.