Cell signaling mediated by the Hedgehog (Hh) family of secreted proteins plays crucial roles in animal development and human diseases. The Hh pathway is operating in a similar way among organisms ranging from insects to human. Drosophila has been a powerful model organism to study Hh signaling mechanisms, as sophisticated genetic, molecular, and biochemical tools are available to dissect this important pathway in whole organisms as well as in cultured cells. The long-term goal of my laboratory is to delineate the complex regulatory network that governs Hh signal transduction in order to understand how graded Hh signal is transduced to generate multiple developmental outputs. Hh exerts its biological influence through a conserved signaling cascade that culminates in controlling the balance between the activator and repressor forms of the transcription factor Ci/Gli (CiA/GliA and CiR/GliR). The goal of this research is to investigate the multifaceted regulatory mechanisms that control Ci activity. Our recent study has uncovered a dual role of the Ser/Thr kinase Fused (Fu) in the regulation of both the production of CiR and the activity of CIA, and revealed that Fu is activated through dimerization-mediated phosphorylation of its activation loop. These findings provide a critical inroad into a mechanistic dissection of Ci activation. We will explore the mechanism by which Fu promotes the maturation of Ci into CiA and investigate how the Hh gradient is translated into a Ci activity gradient (Aim 1). In a genetic modifier screen, we have discovered that the SUMO pathway can modulate Hh signaling activity and identified Ci as a SUMO substrate. We will further characterize this new post-translational modification of Ci to explore its role and mechanism of action in Hh signaling (Aim 2). The molecular mechanism by which Sufu inhibits Ci is still poorly understood. We have uncovered a previously unidentified nuclear localization signal (NLS) that overlaps with the Sufu binding domain in Ci. We will further study the function of this NLS and its regulation (Aim 3). Finally, how Ci functions in the nucleus to control Hh target gene expression has not been fully explored. We have identified multiple domains required for CiR-mediated repression. Identifying cofactors that interact with these domains and investigating their roles in Hh signaling should shed important lights into how Ci regulates its target gene expression. Therefore, we will carry out protein- protein interaction screen and in vivo RNAi screen to identify Ci co-repressors (Aim 4). The proposed study should provide a much deeper understanding of the Hh signal transduction mechanism and shed new light into how graded Hh signals are translated into different developmental outcomes.

Public Health Relevance

The Hh pathway is a major signaling pathway that controls embryonic development and adult tissue homeostasis. Deregulation of Hh signaling has been attributed to many human disorders including birth defects and cancers. Investigation of the multifaceted and conserved mechanisms that regulate Hh signaling activity will not only provide insights into fundamental developmental problems such as how cells interpret different levels of spatial signals but may also provide new avenues for developing diagnostic tools and therapeutic treatments for cancers caused by deregulation of Hh signaling activity.

National Institute of Health (NIH)
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Development - 2 Study Section (DEV2)
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Hoodbhoy, Tanya
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University of Texas Sw Medical Center Dallas
Anatomy/Cell Biology
Schools of Medicine
United States
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Li, Shuang; Ma, Guoqiang; Wang, Bing et al. (2014) Hedgehog induces formation of PKA-Smoothened complexes to promote Smoothened phosphorylation and pathway activation. Sci Signal 7:ra62
Shi, Qing; Han, Yuhong; Jiang, Jin (2014) Suppressor of fused impedes Ci/Gli nuclear import by opposing Trn/Kap?2 in Hedgehog signaling. J Cell Sci 127:1092-103
Chen, Yongbin; Jiang, Jin (2013) Decoding the phosphorylation code in Hedgehog signal transduction. Cell Res 23:186-200
Yue, Tao; Tian, Aiguo; Jiang, Jin (2012) The cell adhesion molecule echinoid functions as a tumor suppressor and upstream regulator of the Hippo signaling pathway. Dev Cell 22:255-67
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Shi, Qing; Li, Shuang; Jia, Jianhang et al. (2011) The Hedgehog-induced Smoothened conformational switch assembles a signaling complex that activates Fused by promoting its dimerization and phosphorylation. Development 138:4219-31
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Ren, Fangfang; Zhang, Lei; Jiang, Jin (2010) Hippo signaling regulates Yorkie nuclear localization and activity through 14-3-3 dependent and independent mechanisms. Dev Biol 337:303-12
Zhang, Qing; Shi, Qing; Chen, Yongbin et al. (2009) Multiple Ser/Thr-rich degrons mediate the degradation of Ci/Gli by the Cul3-HIB/SPOP E3 ubiquitin ligase. Proc Natl Acad Sci U S A 106:21191-6

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