Genetic Screening And Mechanisic Study Of Wnt/Wg And JNK Signaling Pathways Regulators

Cancer is an important disease that threatens human health,with various forms and complex mechanisms,many questions have remained unknown.To explore the pathogenesis of cancer,Drosophila melanogaster was used as a model organism to search for genes related to tumorigenesis and metastasis.The Wnt signaling pathway is highly conserved in evolution,and its abnormality has been implicated in various cancers.The research found that activation of Wnt signaling in Drosophila eyes results in a small-eye phenotype in adults,which was inhibited by overexpression of the E3 ubiquitin ligase POSH(Plenty of SH3 domains).Overexpressing POSH in the wing imaginal discs inhibits the expression of Wnt pathway target genes,and produced a notch phenotype in adult wings that phenotypes reduced Wnt signaling.The genetic epistasis results suggest that POSH may act on Armadillo(Arm),a downstream component of the Wnt pathway.Overexpression of POSH results in reduced Arm protein level both in vivo and in vitro.Biochemical results suggest that POSH could physically interact with Arm and promote K48 ubiquitination-mediated Arm degradation.Finally,in HEK293 T cells,SH3RF1 and SH3RF3,the human orthologs of POSH,also promotes the degradation of the Arm ortholog β-catenin and inhibits the Wnt signaling pathway.Hence,the role and mechanism of POSH in inhibiting the Wnt signaling are highly conserved from fly to Human.In addition,this study identified that two genes regulate cell invasion-dGLYAT and Gp93.The JNK signaling pathway is known to play pivotal roles in tumor invasion.In Drosophila wing imaginal discs,loss of cell polarity in epithelia leads to JNKmediated cell invasion.It was found that knockdown of dGLYAT inhibits JNK signaling-mediated cell invasion.dGLYAT encodes a member of the Gcn5-related Nacetyltransferase(GNAT)family.The GNAT family is involved in histone acetylation,which regulates transcription.After performing m RNA-seq analysis,it was found that knockdown of dGLYAT results in decreased Gadd45 m RNA level.Depletion of Gadd45 also inhibits loss of cell polarity-triggered cell invasion and JNK pathway activation.It was concluded that dGLYAT regulates JNK signaling-mediated cell invasion by modulating Gadd45 transcription.Furthermore,it was found that knockdown of Gp93 results in cell invasion and JNK signaling activation.As a molecular chaperone,Gp93 is required for the proper folding of proteins,while Gp93 depletion leads to impaired protein folding that activates the Unfolded Protein Response(UPR).This study checked three UPR-related pathways,and confirmed that the Ire1-Xbp1 pathway is associated with Gp93 functions.Blocking Ire1-Xbp1 pathway inhibits Gp93 depletion-induced cell invasion and JNK signaling activation,while overexpressing Xbp1 was sufficient to activate cell invasion and JNK signaling.It was concluded that Gp93 regulates JNK signaling-mediated cell invasion via the Ire1-Xbp1 pathway.In summary,by using Drosophila as a model organism,this study characterized three genes,POSH,dGLYAT and Gadd45,that regulate tumorigenesis and progression via the Wnt or JNK pathway.The results presented in this thesis provide insights for human cancer research,and shed light on the design of new strategies and potential drug targets for cancer therapy.