Biochemical Characterization of RolledSem, an Activated Form of Drosophila Mitogen-activated Protein Kinase

Abstract

Sem is more active than Rl following short term as well as prolonged treatment with epidermal growth factor. Interestingly, a more pronounced difference in kinase activity is observed when the proteins are immunoprecipitated from extracts of Drosophila rl and rl Sem larvae. In fact, the kinase activity of Rl Sem from larvae extracts is comparable to the kinase activity of larvae expressing either an activated Sevenless receptor or an activated Raf kinase. We also demonstrate that Dsor1, which has been placed upstream of rl genetically, is able to phosphorylate and activate Rl in vitro.The mitogen-activated protein kinase (MAPK) 1 cascade is a major signaling system by which cells translate extracellular signals into intracellular responses. The mammalian extracellular signal-regulated kinases (ERKs) are the best studied members of the MAP kinase family (for reviews, see Refs. 1 and 2). They are activated by phosphorylation on threonine and tyrosine residues by dual specificity MAPK kinases (MAPKKs). On activation, MAP kinases translocate to the nucleus (3) and activate transcription factors through phosphorylation of serine or threonine residues in the motif P/LXT/SP. One of the best characterized target proteins of MAPK is the ternary complex factor ELK-1, which is phosphorylated by MAP kinases in vitro on sites essential for trans-activation by the serum response element on the c-fos promotor in vivo (4, 5).Many steps of the MAP kinase cascade are conserved in different species, and homologous components have been identified in mammals, yeast, Drosophila melanogaster, and Caenorhabditis elegans. In Drosophila, for example, the specification of the R7 photoreceptor cell fate in each ommatidium of the developing eye is dependent on the components of the MAP kinase cascade. In the R7 precursor cells the Sevenless (Sev) receptor tyrosine kinase is activated by its ligand, the Brideof-sevenless (Boss) protein. The signal is then transduced via Drk (an SH3-SH2-SH3 adaptor protein, homologous to Grb2), Sos, Ras1, and the protein kinases Raf, Dsor1 (MAPKK), and Rl (MAPK) to the nucleus (reviewed in Refs. 6 and 7). A gainof-function mutation in the rl gene, rl Sem , was identified in a genetic screen for dominant mutations that result in the specification of R7 cells in the absence of the inducing signal, the Boss ligand. This dominant mutation is caused by a single amino acid substitution (D334N) in the catalytic domain of the kinase (8). Interestingly, this mutation not only activates the Sev pathway in the developing eye but also induces the formation of additional wing veins and causes female sterility mimicking the activation of the Drosophila EGF receptor homologue (DER) and Torso receptor tyrosine kinases, respectively. Therefore, Rl function is not only necessary but also sufficient to activate multiple receptor tyrosine kinase pathways in Drosophila. The homologue of the MAP kinase activating kinase (MAPKK) encoded by the Dsor1 gene is also required for multiple developmental pathways (9). Using a temperatu...

Mapping the binding interface of ERK and transcriptional repressor Capicua using photocrosslinking

“…This mutation, termed the sevenmaker mutation, was first identified in a screen for gain-of-function mutants in Drosophila that rescue ERK-dependent eye development in the absence of upstream components of the ERK signaling pathway (34). This mutation has been shown to weaken the interaction between ERK and DRS-interacting proteins, especially regulators of ERK, including a number of phosphatases (14,21,(35)(36)(37)(38)(39)(40). Thus, it appears that both Cic and ERK phosphatases recognize overlapping surfaces in ERK, although possibly involving different amino acid contacts.…”

ERK as a Model for Systems Biology of Enzyme Kinetics in Cells

“…The sevenmaker gain of function mutant of ERK was discovered in a genetic screen performed in Drosophila (68, 69). The mutation was found to lie in one of the ERK docking domains, the DRS.…”

“…However, increased activity may arise from an imbalance of this effect on different ERK-interacting proteins. It is possible that deactivation of ERK by phosphatases is more sensitive to disruption of the DRS than activation by kinases or catalysis by ERK (69, 70). Thus, even if all binding interactions involving the DRS are negatively impacted by the sevenmaker mutation, if the disruption is more pronounced in ERK phosphatases relative to ERK’s other binding partners, the ratio of active to inactive ERK increases.…”

Negative Regulation of EGFR/MAPK Pathway by Pumilio in Drosophila melanogaster

“…Extra wing veins also arise when EGFR/Ras/MAPK signaling is enhanced [3], [21]. For example, a gain of function mutant, rl [Sem] heterozygotes ( rl [Sem] /+) with elevated MAPK activity [3], [22] produces extra vein material (Figure 1E) (penetrance >90%, n>10). In addition, wing veins arose in the posterior compartment of the wing when Ras was expressed by en-Gal4 ( en-gal4 / UAS-Ras ) (Figure 1H).…”