A genome-wide RNAi screen identifies MASK as a positive regulator of cytokine receptor stability

Abstract

In order for cells to sense and thus respond to their environment, they require transmembrane receptors, which bind extracellular ligands and then transduce this signal within the cell. A subset of receptors, with single-pass transmembrane domains are known as cytokine receptors and act via the Janus Kinase and Signal Transducer and Activator of Transcription (JAK/STAT) pathway. These receptors are essential for processes such as haematopoiesis, immune responses and tissue homeostasis. In order to transduce ligand activation, cytokine receptors must dimerise. However, mechanisms regulating their dimerisation are largely unknown. In order to better understand the processes regulating cytokine receptor levels, activity and dimerisation, we used the highly conserved JAK/STAT pathway in Drosophila, which acts via a single receptor, known as Domeless. We have performed a genome-wide RNAi screen in Drosophila cells, identifying MASK as a positive regulator of Domeless dimerisation and protein levels. We show that MASK is able to regulate JAK/STAT signalling both in vitro and in vivo. We go on to show that MASK is able to bind to Domeless via its Ankyrin repeat domains and alters the stability of the receptor. Finally, we extend our observations to the human homologue, ANKHD1, and demonstrate functional conservation, with ANKHD1 able to regulate JAK/STAT signalling and the levels of a subset of pathway receptors in human cells. Taken together, we have identified MASK as a conserved regulator of cytokine receptor levels, which may have implications for human health.