Disease relevance of CNKSR1

• Immunoprecipitates of MST1 endogenous to LoVo colon cancer cells contain endogenous CNK1; however, no association of these two polypeptides can be detected in a yeast two-hybrid assay [1].

High impact information on CNKSR1

• KSR overexpression constitutively activates Raf-1 [2].
• Kinase suppressor of Ras (KSR) is a conserved component of the Ras pathway that interacts directly with MEK and MAPK [3].
• Human CNK1 acts as a scaffold protein, linking Rho and Ras signal transduction pathways [4].
• Association of CNK1 with Rho guanine nucleotide exchange factors controls signaling specificity downstream of Rho [5].
• Down-regulation of endogenously expressed CNK1 by small inhibitory RNA interferes with Src-dependent activation of ERK [6].

Biological context of CNKSR1

• The connector enhancer of KSR (CNK) is a multidomain scaffold protein discovered in Drosophila, where it is necessary for Ras activation of the Raf kinase [1].
• Overexpression of CNK1-(1-282), a fragment that binds RASSF1A but is not proapoptotic, blocks the apoptosis induced by CNK1 and by Ki-Ras(G12V) [1].
• The scaffold protein CNK1 interacts with the tumor suppressor RASSF1A and augments RASSF1A-induced cell death [1].
• Phosphoamino acid analysis identified serine as the major target, and two peaks of Nm23-H1 phosphorylation were identified upon high performance liquid chromatography analysis of KSR tryptic peptides [7].
• Bioluminescence resonance energy transfer identify scaffold protein CNK1 interactions in intact cells [8].

Anatomical context of CNKSR1

• Overexpression of hCNK1 does not affect the actin cytoskeleton and does not modify the appearance of stress fibers in cells overexpressing a constitutively active form of RhoA [8].
• Microarray and quantitative polymerase chain reaction-based gene expression profiling demonstrates that definitive endoderm formation under these conditions closely parallels that following specification with elevated Activin A and low fetal calf serum (FCS)/knockout serum replacement (KSR) [9].

Associations of CNKSR1 with chemical compounds

• In vitro, low nanomolar concentrations of natural ceramide stimulate KSR to autophosphorylate, and transactivate Raf-1 [2].
• In vitro, KSR specifically phosphorylated c-Raf-1 on threonine residues during the first stage of the two-stage kinase assay [10].
• The scaffold protein CNK1 interacts with the angiotensin II type 2 receptor [11].
• The exchange of a conserved leucine residue with arginine in the CRIC domain increases the binding affinity of CNK1 to the AT2 receptor [11].

Physical interactions of CNKSR1

• In this work, using in vivo bioluminescence resonance energy transfer (BRET) assays and in vitro co-immunoprecipitation, we show that hCNK1 interacts with the active form of Rho A (G14V) proteins [8].
• CNK1 binds preactivated Raf-1 and activated Src and forms a trimeric complex [6].

Regulatory relationships of CNKSR1

• CNK1 regulates the activation of Raf-1 by Src in a concentration-dependent manner typical for a scaffold protein [6].

Other interactions of CNKSR1

• In contrast, hCNK1 was able to significantly decrease the RhoA-induced transcriptional activity of the serum response element (SRE) without effect on the Ras-induced SRE activation [8].
• Thus, CNK1 allows cross-talk between Src and Raf-1 and is essential for the full activation of Raf-1 [6].

Analytical, diagnostic and therapeutic context of CNKSR1

• Using site-directed mutagenesis, we found that Nm23-H1 phosphorylated KSR serine 392, a 14-3-3-binding site, as well as serine 434 when serine 392 was mutated [7].

References