Hip Hop: Hipk promotes tumourigenesis in Drosophila through JAK/STAT signaling

Signal transduction pathways are crucial for co-ordinated development and growth of multicellular organisms. Dysregulation and mutations of components in these pathways can often lead to tumourigenesis. Evolutionarily conserved Homeodomain-Interacting-Protein-Kinase (Hipk) is a strong growth regulator of many signal transduction pathways, and elevated levels of hipk lead to tumour-like masses. While many known regulators of Hipk exist, we attempted to identify novel phospho-regulators of Hipk activity. Here we present evidence that Hopscotch, a core tyrosine kinase of the JAK/STAT cascade, is a putative phospho-regulator of Hipk activity in multiple contexts. We show that modulation of Hipk expression levels modifies JAK/STAT activity in both wildtype and tumourous tissues. Finally, we show that Hipk interacts with the JAK/STAT transcriptional effector STAT92E. Thus, our work provides a role for Drosophila Hipk in tumourigenesis and regulation of the JAK/STAT cascade.