ABSTRACT
Cadherin-mediated cell-cell adhesion is dynamically modulated during epithelial-mesenchymal transition triggered by activation of receptor tyrosine kinases (RTK) in epithelial cells. Several cadherin-binding proteins have been identified that control cell-cell adhesion. However, the mechanisms by which intercellular adhesion and cell motility are coregulated are still unknown. Here, we delineate a hitherto uncharted cooperation between RTKs, RhoA GTPase, and p120 catenin in instructing a motile behavior to epithelial cells. We found that expression of an N-terminus-deleted p120 catenin in a variety of epithelial cell types, including primary keratinocytes, effectively competes for endogenous p120 at cadherin binding sites and abrogates EGF-stimulated cell motility as well as HGF-induced cell scattering. The deleted mutant also inhibits the PI3K-dependent RhoA activation ensuing receptor activation. Conversely, we also show that the ectopic expression of full-length p120 in epithelial cells promotes cytoskeletal changes, stimulates cell motility, and activates RhoA. Both motogenic response to p120 and RhoA activation require coactivation of signaling downstream of RTKs as they are suppressed by ablation of the Ras/PI3K pathway. These studies demonstrate that p120 catenin is a necessary target of RTKs in regulating cell motility and help define a novel pathway leading to RhoA activation, which may contribute to the early steps of metastatic invasion.
Subject(s)
Cell Adhesion Molecules/metabolism , Cell Movement/physiology , Keratinocytes/metabolism , Phosphoproteins/metabolism , Animals , Catenins , Cell Adhesion Molecules/genetics , Epidermal Growth Factor/metabolism , Hepatocyte Growth Factor/metabolism , Mice , Mutation , Phosphoproteins/genetics , rac GTP-Binding Proteins/metabolism , rhoA GTP-Binding Protein/metabolism , Delta CateninABSTRACT
The cloning and sequencing of complementary DNAs corresponding to the two copies (a and b) of the Xenopus laevis gene for hnRNP E2 is presented. Comparison of the two sequences reveals that while they are somewhat divergent at the nucleotide level, they are very conserved at the amino acid level. The analysis also showed two transcripts of different length (alpha and beta), likely generated by alternative processing. There are indications that either gene copy can generate both type of transcripts. Northern blot analysis in oocytes and developing embryos showed that hnRNP E2 RNA is constantly present and that increases in amount at tadpole stage. A semiquantitative reverse transcriptase polymerase chain reaction analysis performed with RNA from developing embryos showed that long (alpha) transcript accumulation is constant during development, whereas the short one (beta) accumulation increases at later stages, thus determining the observed increase in total RNA. Nucleo-cytoplasm localization experiments indicated that in oocyte hnRNP E2 is exclusively cytoplasmic, whereas in somatic cells it is distributed in both compartments. Comparison of the amino acid sequence of the two X. laevis hnRNP E2 with the corresponding mammalian sequences shows a high homology along the molecule except for the region subjected to alternative splicing, which is completely different. Moreover, there are indications that the homologous of mammalian hnRNP E1 gene, very related to and derived from hnRNP E2 by retrotransposition, is not expressed or even not present in X. laevis, suggesting that mammalian hnRNP E1 gene may have originated after mammal/amphybia divergence.
