Modulation of KSR activity in Caenorhabditis elegans by Zn ions, PAR-1 kinase and PP2A phosphatase

Abstract

Vulval differentiation in Caenorhabditis elegans is controlled by a conserved signal transduction pathway mediated by Ras and a kinase cascade that includes Raf, Mek and MAPK. Activation of this cascade is positively regulated by a number of proteins such as KSR (kinase suppressor of Ras), SUR‐8/SOC‐2, SUR‐6/PP2A‐B and CDF‐1. We describe the functional characterization of sur‐7 and several genes that regulate signaling downstream of ras. We identified sur‐7 by isolating a mutation that suppresses an activated ras allele, and showed that SUR‐7 is a divergent member of the cation diffusion facilitator family of heavy metal ion transporters that is probably localized to the endoplosmic recticulum membrane and regulates cellular Zn2+ concentrations. Genetic double mutant analyses suggest that the SUR‐7‐mediated effect is not a general toxic response. Instead, Zn2+ ions target a specific step of the pathway, probably regulation of the scaffolding protein KSR. Biochemical analysis in mammalian cells indicates that high Zn2+ concentration causes a dramatic increase of KSR phosphorylation. Genetic analysis also indicates that PP2A phosphatase and PAR‐1 kinase act downstream of Raf to positively and negatively regulate KSR activity, respectively.

Identification of Mutations in Caenorhabditis elegans That Cause Resistance to High Levels of Dietary Zinc and Analysis Using a Genomewide Map of Single Nucleotide Polymorphisms Scored by Pyrosequencing

“…Zinc has also been implicated in signaling processes and may be a signaling molecule: zinc is concentrated in some synaptic vesicles and then released into the synapse where it might modulate neurotransmission (Frederickson and Bush 2001;Colvin et al 2003;Wall 2005;Yamasaki et al 2007). Zinc affects epidermal growth factor receptor/Ras-mediated signal transduction, thus playing a role in cell fate determination (Wu et al 1999;Bruinsma et al 2002;Samet et al 2003;Yoder et al 2004). The importance of the processes that involve zinc is demonstrated by the observation that severe zinc deficiency is incompatible with growth and survival.…”

“…Two genes that encode members of the CDF family have been demonstrated to play a role in zinc metabolism: cdf-1 and sur-7. cdf-1(lf) and sur-7(lf) mutants display dose-dependent developmental delays when cultured on standard nematode growth media supplemented with zinc, indicating that these genes are necessary for zinc tolerance (Bruinsma et al 2002, Yoder et al 2004. Mutations of both genes were identified in genetic screens for mutants with abnormal vulval formation, and both genes play a role in Ras-mediated signaling during vulval development.…”

Caenorhabditis elegans CNK-1 promotes Raf activation but is not essential for Ras/Raf signaling

“…and before activating phosphorylation in the kinase domain. This placement is distinct from sur-8, which is required upstream of the dephosphorylation event (45) and ksr-1 and sur-6, which are required downstream of activating phosphorylation in the kinase domain. ksr-1 and sur-6 could also have additional, upstream requirements.…”

Nucleoside diphosphate kinases (NDPKs) in animal development

“…Moreover, cancer invasion induced by NM23-H1 silencing was reverted by a pharmacological inhibitor of the Ras/ ERK pathway, further showing an inverse relationship between NDPK activity and Ras/ERK activation in human [67]. Structural differences in worm and mammalian KSRs might lead to altered regulation of these scaffold proteins [68,69]. Furthermore, the mechanisms of Raf activation, which is proposed to occur through Raf dimerization [70], might not be evolutionary conserved as the nematode possess only a single B-Raf homolog whereas in mammalian systems, 3 Raf isoforms are present [69].…”