Addressing How Cindr Suppresses JNK Activity in Drosophila

<p>Epithelial tissues provide essential barriers against chemical toxins, microbial pathogens, UV radiation and mechanical stress. Understanding how epithelial cells maintain their positions under environmental stress is relevant in studying certain cancer models. Previous studies conducted in the Johnson lab examined a novel interaction between the adaptor protein Cindr and the JNK signaling pathway in Drosophila epithelia. Adaptor proteins act as scaffolds for signal transduction pathways to orchestrate the assembly of specific protein complexes. JNK is the terminal kinase in a highly conserved signal transduction pathway. This pathway transduces signals that stimulate a variety of cell behaviors, including cell migration, proliferation and apoptosis. Members of the Johnson lab were the first to report that Cindr has an inhibitory effect on JNK activity to maintain epithelial sheet integrity. Additionally, independent yeast-two hybrid studies reported an interaction between Cindr and Drosophila JNK. However, the molecular mechanism underlying the Cindr-JNK interaction remained elusive because Cindr, as an adaptor protein, lacks inherent enzymatic abilities. This begs the question: How does Cindr modulate JNK activity?</p> <p>In this study we investigate three models addressing how Cindr represses JNK activity by sequestration, deactivation or degradation. We used gel electrophoresis and western blotting to investigate whether modifying the levels of Cindr changed the levels of JNK. We found that there was a decrease in JNK when Cindr was over expressed and an increase when Cindr was reduced. This supported our model where Cindr’s inhibitory role on JNK was mediated by an E3 ubiquitin ligase. To establish an inventory of potential candidates we conducted a genetic modifier screen. This approach identified the ubiquitin ligases No poles, Parkin and Traf6 as potential candidates. Both Parkin and Traf6 suppressed the cindrRNAi phenotype in the pupal eye. Thus, these ubiquitin ligases may be recruited by Cindr to fine tune JNK activity. These findings may provide insights into the molecular events in emerging epithelial cancers.</p>