The dual-specificity tyrosine-phosphorylation-regulated kinase, DYRK1B, is expressed de novo during myogenesis, amplified or mutated in certain cancers and mutated in familial cases of metabolic syndrome. DYRK1B is activated by cis auto-phosphorylation on tyrosine-273 (Y273) within the activation loop during translation but few other DYRK1B phosphorylation sites have been characterised to date. Here, we demonstrate that DYRK1B also undergoes trans-autophosphorylation on serine-421 (S421) in vitro and in cells and that this site contributes to DYRK1B kinase activity. Whilst a DYRK1BS421A mutant was completely defective for p-S421 in cells, DYRK1B inhibitors caused only a partial loss of p-S421 suggesting the existence of an additional kinase that could also phosphorylate DYRK1B S421. Indeed, a catalytically inactive DYRK1BD239A mutant exhibited very low levels of p-S421 in cells but this was increased by KRASG12V. In addition, selective activation of the RAF-MEK1/2-ERK1/2 signalling pathway rapidly increased p-S421 in cells whereas activation of the stress kinases JNK or p38 could not. S421 resides within a Ser-Pro phosphoacceptor motif that is typical for ERK1/2 and recombinant ERK2 phosphorylated DYRK1B at S421 in vitro. Our results show that DYRK1B is a novel ERK2 substrate, uncovering new links between two kinases involved in cell fate decisions. Finally, we show that DYRK1B mutants that have recently been described in cancer and metabolic syndrome exhibit normal or reduced intrinsic kinase activity.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-015-2032-x) contains supplementary material, which is available to authorized users.

The dual-specificity kinase DYRK3 controls formation and dissolution of several intracellular condensates thereby regulating various cell physiological processes. Here we report that DYRK3 establishes a dynamic equilibrium between condensation and dissolution of proteins associated with membranous structures of the early secretory pathway to organize membrane traffic between the ER and the Golgi complex in mammalian cells. This depends on the peripheral membrane protein Sec16A, whose N-terminal disordered region forms DYRK3-controlled liquid-like condensates on the surface of the ER and co-phase separates with multiple ER exit site components and a subset of matrix proteins specifically associated with ERGIC and cis-Golgi. Our findings support a mechanism whereby multiple interacting and differentially regulated intracellular condensates create favorable environments for directional membrane traffic in eukaryotic cells.Recently, liquid-liquid phase separation (LLPS) has emerged as a general mechanism to locally concentrate multiple factors involved in complex biochemical processes (17)(18)(19)(20).This typically involves weak multivalent interactions between proteins with intrinsically disordered regions (IDRs)(21-24). The resulting biomolecular condensates display rapid, liquid-like merging and can exchange components between the condensed and the dilute phase within seconds. Sec16A is also a highly disordered protein, with ~75% of its total sequence predicted to be disordered in both S. cerevisiae and H. sapiens, as well as other ERES proteins including the transmembrane proteins TANGO1L (transport and Golgi organization protein 1) and cTAGE5 (cutaneous T cell lymphoma-associated antigen 5) (25,26). Moreover, ERES components can exchange with a cytosolic pool within seconds, and individual ERES can rapidly merge with each other(27-29). Thus, the mechanism by which Sec16A acts as a central organizer of ERES may involve LLPS, which drives the formation of ER-associated biomolecular condensates that locally concentrate ERES proteins and COPII vesicle coat components. This behavior may also underlie the formation of Sec bodies in drosophila S2 cells, which are membraneless organelles formed by Sec16A during amino acid starvation(30). In addition, some COPII coat components partition into stress granules(31), which are membraneless organelles formed by LLPS during stress(32, 33), suggesting an affinity for biomolecular condensates.As recently suggested(34), LLPS may also underly the formation of the Golgi matrix (35). This matrix consists of golgins, which are transmembrane or membrane-associated proteins with long coiled-coil regions in their cytosolic domains (36,37). The cis-golgin GM130 has recently been shown to undergo LLPS in vitro and when overexpressed in cells(38). Similarly, TFG1 (Trk-fused gene 1), which interacts with Sec16A(39), forms a matrix at the interface between the ER and the ER-Golgi Intermediate Compartment (ERGIC) through oligomerization of C-terminal PQ (proline-glutamine)-rich IDRs (40,41)....

PDZ domains are involved in many cellular processes and are key regulators of the cell physiology. A huge number of studies have investigated the binding specificity of PDZ domains to the carboxyl-terminal sequence of target proteins, while the molecular mechanisms that mediate the recognition of internal binding regions are largely unexplored. In the present study, we describe a ligand motif located in the catalytic domain of the phosphatase Dusp26 which mediates its binding to the PDZ-4 of Scribble. Site-directed mutagenesis identified a conserved tyrosine residue as relevant for the binding. The interaction with the PDZ domain could help the phosphatase to recruit its specific targets.

The DUSP26 gene encodes for an atypical dual specificity phosphatase commonly referred to as Dusp26 or MPK8. Although its physiological role is poorly understood, different substrates have been reported to be dephosphorylated by Dusp26, including p53, Kif3, Erk and p38. In this report we summarize the current knowledge on DUSP26 gene, its transcripts, the encoded protein and its function in normal and tumorous tissues. Notably, the phosphatase is overexpressed in neuroblastoma and ATC cells, where it promotes chemoresistance by inhibiting the p53 and the p38 proteins, respectively. Dusp26 represents a promising novel therapeutic target to be integrated with others and with conventional medicine, to improve survival outcome in patients and to reduce toxicity.