The interaction of cells with the extracellular matrix regulates cell shape, motility, growth, survival, differentiation and gene expression, through integrin-mediated signal transduction. We used a two-hybrid screen to isolate genes encoding proteins that interact with the beta 1-integrin cytoplasmic domain. The most frequently isolated complementary DNA encoded a new, 59K serine/threonine protein kinase, containing four ankyrin-like repeats. We report here that this integrin-linked kinase (ILK) phosphorylated a beta 1-integrin cytoplasmic domain peptide in vitro and coimmunoprecipitated with beta 1 in lysates of mammalian cells. Endogenous ILK kinase activity was reduced in response to fibronectin. Overexpression of p59ILK disrupted epithelial cell architecture and inhibited adhesion to integrin substrates, while inducing anchorage-independent growth. We propose that ILK is a receptor-proximal protein kinase regulating integrin-mediated signal transduction.

The integrin-linked kinase (ILK) is an ankyrin repeat containing serine-threonine protein kinase that can interact directly with the cytoplasmic domains of the ␤1 and ␤3 integrin subunits and whose kinase activity is modulated by cell-extracellular matrix interactions. Overexpression of constitutively active ILK results in loss of cell-cell adhesion, anchorage-independent growth, and tumorigenicity in nude mice. We now show that modest overexpression of ILK in intestinal epithelial cells as well as in mammary epithelial cells results in an invasive phenotype concomitant with a down-regulation of Ecadherin expression, translocation of ␤-catenin to the nucleus, formation of a complex between ␤-catenin and the high mobility group transcription factor, LEF-1, and transcriptional activation by this LEF-1͞␤-catenin complex. We also find that LEF-1 protein expression is rapidly modulated by cell detachment from the extracellular matrix, and that LEF-1 protein levels are constitutively up-regulated at ILK overexpression. These effects are specific for ILK, because transformation by activated H-ras or v-src oncogenes do not result in the activation of LEF-1͞␤-catenin. The results demonstrate that the oncogenic properties of ILK involve activation of the LEF-1͞␤-catenin signaling pathway, and also suggest ILK-mediated cross-talk between cellmatrix interactions and cell-cell adhesion as well as components of the Wnt signaling pathway.The integrin-linked kinase (ILK) was identified from a yeast two-hybrid genetic screen by using as bait the cytoplasmic domain of the ␤ 1 integrin subunit (1). ILK can interact with ␤ 1 and ␤ 3 integrins (1). ILK is a novel ankyrin-repeat containing serinethreonine kinase (1), which also contains sequence motifs found in pleckstrin homology domains capable of interacting with phosphoinositide lipids. The kinase activity of ILK can be modulated by interaction of cells with components of the extracellular matrix (1) or by integrin clustering. The activation or inhibition of ILK activity is cell-type dependent and can be modified by growth factors (M. Delcommenne and S. D., unpublished results). Overexpression of ILK in epithelial cells results in the stimulation of anchorage-independent cell growth (1) and cell cycle progression (2). The latter is caused by the constitutive up-regulation of expression of cyclin D 1 and cyclin A, resulting in the hyperphosphorylation of the retinoblastoma protein (2). Overexpression of ILK in epithelial cells also results in the induction of tumorigenicity in nude mice (3), indicating that ILK is a protooncogene.