Protein kinase CK1 interacts with and phosphorylates RanBPM in vitro

Members of the casein kinase 1 (CK1) family of serine/threonine kinases are highly conserved from yeast to mammals and are involved in the regulation of various cellular processes. Specifically, the CK1 isoforms δ and ε have been shown to be involved in the regulation of proliferative processes, differentiation, circadian rhythm, as well as in the regulation of nuclear transport. In this report we show that CK1δ and ε interact with murine RanBPM in the yeast two-hybrid system (YTH) and that the putative CK1δ-interacting domains of RanBPM are located between aa 155-386 and aa 515-653. Furthermore, in mammalian cells CK1δ partially co-localizes with RanBPM and can be coimmunoprecipitated with RanBPM. In addition, CK1δ strongly phosphorylates RanBPM within aa 436-514 in vitro. The identification of the interacting and scaffolding protein RanBPM as a new substrate of CK1δ points towards a possible function for CK1δ in modulating RanBPM specific functions