Role of integrins in differentiation of chick retinal pigmented epithelial cells in vitro

When retinal pigmented epithelial cells (PEG) of chick embryos are cultured under appropriate conditions, the phenotype changes to that of lens cells through a process known as transdiiferentiation. The first half of the process, characterized by dedifferentiation of PEG, is accompanied by a marked decrease in adhesiveness of PEC to collagen type I- or type IV-coated dishes. To understand the underlying mechanisms of this change, we analyzed the expression of integrins, which are major receptors for extracellular matrix components. Northern blot analysis with cDNA probes for chicken alpha 3, alpha 6, alpha 8, alpha v, beta 1 and beta 5 integrin mRNA showed that the genes for all these integrins are transcribed at similar levels in PEC and dedifferentiated PEC (dePEC). Further analysis of beta 1 integrin, which is a major component of integrin heterodimers, showed that although the protein amount of beta 1 integrin was not changed, its localization at focal contacts seen in PEC was lost in dePEC. When anti-beta 1 integrin antibody was added to the PEC culture medium, a decrease of cell-substrate adhesiveness occurred, followed by a gradual change in both morphology and gene expression patterns to ones similar to those of dePEC. These findings suggest that an appropriate distribution of beta 1 integrin plays an essential role in maintaining the differentiated state of PEC through cell-substrate adhesion.