Integrin-Linked-Kinase Binding Proteins Are Essential Components Of The Cardiac Mechanical Strech Sensor

The cardiac strech sensor enables the heart to adapt its force of contraction to continually changing demands. We recently identified in the zebrafish mutant main squeeze (msq) Integrin-Linked-Kinase (ILK) as a component of this strech sensor. Mutations in zebrafish ilk lead to down-regulation of stretch responsive cardiac genes and cause progressive heart failure. Antisense-mediated abrogation of zebrafish β-parvin, which forms complexes with ILK, phenocopies ilk mutant zebrafish. We here describe two novel ILK-binding-proteins, acting in concert with ILK to control cardiac contractility. In a yeast-to-hybrid-screen with a cardiac specific library we identified two ILK-binding proteins (ILK-bp-1 and ILK-bp-2). Just as we have recently shown for ILK, ILK-bp-1/2 are highly expressed in the zebrafish heart and localize at the sarcomeric Z-disc. To reveal the in vivo function of ILK-bp-1/2 we performed knock-down studies on zebrafish with antisense oligonucleotide injection. Similar to the phenotype of ILK-deficient zebrafish, the knock down of ILK-bp-1/2 leads to loss of cardiac contractility and, as shown by in-situ-hybridisation, to down-regulation of the stretch responsive gene anf. We analysed the ILK-bp-1/2 morphant hearts structurally and ultra-structurally. Just as we have recently shown for ilk deficient hearts, we found that their morphogenesis and myofibrillogenesis are normal, indicating that knock-down of ILK-binding-proteins does not induce a structural but rather a functional heart defect. Taken together, these results indicate, that next to β-parvin other ILK-binding proteins play important roles in the control of heart contractility. ILK and ILK-bp-1/2 act in concert to enable the heart to adapt itself to continually changing demands.