Role of the Integrin-Linked Kinase, ILK, in Mammary Carcinogenesis.

ILK-1 is a protein serinethreonine kinase which regulates integrin and growth factor signaling in epithelial cells. Recent evidence suggests that protein kinase B and glycogen synthase kinase 3-B are ILK-1 substrates. ILK-1 has been shown to phosphorylate PKB on Ser473 in vitro, and to stimulate this phosphorylation in vivo. ILK-1 is thus a strong candidate phospholipid-dependent kinase 2 PDK2 molecule. We have cloned a serinethreonine phosphatase belonging to the PP2C family, which forms stable complexes with p5ILK-1 protein in epithelial cells. This association is demonstrated in yeast two-hybrid experiments, in vitro pull-down assays, and by co-immunoprecipitation from epithelial cell lysates. It is likely that this PP2C isoform specifically regulates ILK catalytic activity in these complexes, thereby suppressing the pro-apoptotic activity of PKB by inhibiting the PDK2 activity of ILK- 1. A second ILK-1 interacting protein has been identified, which may provide insights into regulation of the actin cytoskelton by integrins and ILK-1. This protein is ca. 35 kDa, comprised primarily of 2 calponin homology domains. These domains have been implicated in actin binding by a number of proteins, including spectrin, fodrin and a-actinin. This association is also likely to reflect a direct interaction with p59ILK-1, detectable in yeast two-hybrid and in vitro pull-down experiments.