Defining the full complement of substrates for each ubiquitin ligase remains an important challenge. Improvements in mass spectrometry instrumentation and computation and in protein biochemistry methods have resulted in several new methods for ubiquitin ligase substrate identification. Here we used the parallel adapter capture (PAC) proteomics approach to study βTrCP2, a substrate adaptor for the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase complex. The processivity of the ubiquitylation reaction necessitates transient physical interactions between βTrCP2 and its substrates, thus making biochemical purification of FBXW11-bound substrates difficult. Using the PAC-based approach, we inhibited the proteasome to “trap” ubiquitylated substrates on the SCF (βTrCP2) E3 complex. Comparative mass spectrometry analysis of immunopurified βTrCP2 protein complexes before and after proteasome inhibition revealed 21 known and 23 putatively novel substrates. Interestingly, many novel substrates for βTrCP2, including TBC1D4, HCFC1, DENND4C, FNIP1, and FLCN are related to cell metabolism. TBC1D4 encodes a GTPase activating protein for the small GTPase Rab that controls insulin-dependent trafficking of the GLUT4 glucose transporter in adipocytes. DENND4C acts as a guanine nucleotide exchange factor for Rab10 and its activity is required for insulin-stimulated GLUT4 translocation to plasma membrane in adipocytes. HCFC1 is a member of the host cell factor family, affecting gluconeogenesis by modulating PGC-1α stability. These suggest βTrCP2 might play important roles in glucose homeostasis by regulating stability of several different target proteins. Here, in focused study, we found that βTrCP1/2 bound, polyubiquitylated, and destabilized FNIP1, FLCN interacting protein 1. We further demonstrated that FNIP1 degradation was promoted by AMPK activation after glucose depletion and expression of a degradation-resistant FNIP1 mutant results in sustained activation of mTORC1 signaling. Hence, our findings reveal that βTrCP1/2 is involved in nutrient sensing through the AMPK-FLCN-FNIP1 and mTORC1 signaling pathways. Citation Format: Tai Young Kim, Jee Yun Chang, Jin Mo Ku, Se Hyang Hong, ji Hye Kim, Hyeong Sim Choi, Kangwook Lee, Myeong-Sun Kim, Sang Mi Woo, Michael B. Major, Seong-Gyu Ko. Substrate trapping proteomics reveals novel mechanism for regulation of mTORC1 signaling by βTrCP-FNIP1/2-FLCN axis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4543.

Pancreatic cancer has a poor prognosis and very low survival rate over the world. Because pancreatic cancer probably is diagnosed at a late stage, aggressive local invasion, and poor response to chemotherapy. Gemcitabine was the standard treatment for advanced and metastatic pancreatic cancer patients, but it is associated with multiple adverse effects-fever, fatigue, nausea, and drug resistance. Whether cucurbitacin D has any efficacy against human pancreatic cancer was examined in cell culture system. In vitro, cell viability was measured by MTT assay to recognize of cell cytotoxicity. Consequently, cytotoxicity was observed at a low concentration of cucurbitacin D. Wound healing assay and clonogenic assay indicated that cucurubitacin D inhibited the growth of cell growth through cyclins and CDKs regulation, and decreased colony-forming ability. Also, this compound down-regulated expression level of anti-apoptotic protein, Bcl-2, up-regulated of pro-apoptotic molecule Bax, and activated caspase-8, caspase-3 cascade extrinsic pathway. Additionally, PARP, caspase-3 substrate, protein was cleaved by cucurbitacin D treatment. Overall, our study suggest that cucurbitacin D could be a clinical medicine for the treatment of pancreatic cancers. Citation Format: Myeong-Sun Kim, Ji Hye Kim, Jin Mo Ku, Se Hyang Hong, Kangwook Lee, Hyeong Sim Choi, Sang Mi Woo, Jee Yun Chang, Tai Young Kim, Seong Gyu Ko Ko. Cyclins and CDKs regulation and caspase cascade activation by cucurbitacin D induced cell cycle arrest and apoptosis in pancreatic tumor. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3522.