In vivo inactivation of MASTL kinase results in thrombocytopenia.

OBJECTIVE: A missense mutation in the microtubule-associated serine/threonine-like kinase gene (MASTL, FLJ14813) on human chromosome 10 was previously linked to a novel form of autosomal dominant inherited thrombocytopenia in a single pedigree. The mutation results in an amino acid change from glutamic acid at position 167 to aspartic acid and segregates perfectly with thrombocytopenic individuals within this extended family. The phenotype is characterized by mild thrombocytopenia with an average platelet count of 60,000 platelets per microliter of blood. We wanted to determine the expression and localization of MASTL, as well as its role in developing thrombocytes using an in vivo model system. MATERIALS AND METHODS: Northern blot analysis allowed us to examine expression patterns. Morpholino knockdown assays in zebrafish (Danio rerio) were employed to determine in vivo contribution to thrombocyte development. Transient expression in baby hamster kidney cells resulted in localization of both the wild-type and E167D mutant forms of MASTL kinase to the nucleus. RESULTS: Northern blot analysis indicates that MASTL messenger RNA is restricted in its expression to hematopoietic and cancer cell lines. A transient knockdown of MASTL in zebrafish results in deficiency of circulating thrombocytes. Transient expression of recombinant MASTL kinase in vitro demonstrates localization to the nucleus. CONCLUSIONS: Functional studies presented here demonstrate a direct relationship between transient knockdown of MASTL kinase gene expression and reduction of circulating thrombocytes in zebrafish. This transient knockdown of MASTL in zebrafish correlates with a decrease in the expression of the thrombopoietin receptor, c-mpl, and the CD41 platelet adhesion protein, GpIIb, but has no effect on essential housekeeping zebrafish gene, EF1alpha.

Pellino 1 is required for interleukin-1 (IL-1)-mediated signaling through its interaction with the IL-1 receptor-associated kinase 4 (IRAK4)-IRAK-tumor necrosis factor receptor-associated factor 6 (TRAF6) complex.

The signaling pathway downstream of the mammalian interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) is evolutionally conserved with that mediated by the Drosophila Toll protein. Toll initiates its signal through the adapter molecule Tube and the serine-threonine kinase Pelle. Pelle is highly homologous to members of the IL-1R-associated kinase (IRAK) family in mammals. Recently, a novel Pelle-interacting protein called Pellino was identified in Drosophila. We now report a mammalian counterpart of Pellino, termed Pellino 1, which is required for NF kappa B activation and IL-8 gene expression in response to IL-1, probably through its signal-dependent interaction with IRAK4, IRAK, and the tumor necrosis factor receptor-associated factor 6 (TRAF6). The Pellino 1-IRAK-IRAK4-TRAF6 signaling complex is likely to be intermediate, located between the IL-1 receptor complex and the TAK1 complex in the IL-1 pathway.