Molecular-glue degraders mediate interactions between target proteins and components of the ubiquitin-proteasome system to cause selective protein degradation. Here, we report a new molecular glue HQ461 discovered by high-throughput screening. Using loss-of-function and gain-of-function genetic screening in human cancer cells followed by biochemical reconstitution, we show that HQ461 acts by promoting an interaction between CDK12 and DDB1-CUL4-RBX1 E3 ubiquitin ligase, leading to polyubiquitination and degradation of CDK12-interacting protein Cyclin K (CCNK). Degradation of CCNK mediated by HQ461 compromised CDK12 function, leading to reduced phosphorylation of a CDK12 substrate, downregulation of DNA damage response genes, and cell death. Structure-activity relationship analysis of HQ461 revealed the importance of a 5-methylthiazol-2-amine pharmacophore and resulted in an HQ461 derivate with improved potency. Our studies reveal a new molecular glue that recruits its target protein directly to DDB1 to bypass the requirement of a substrate-specific receptor, presenting a new strategy for targeted protein degradation.

The collapse in trade and the contraction of output that occurred during 2008-9 was comparable to, and in many countries more severe than, the Great Depression of the 1930s. However, it did not give rise to the rampant protectionism that followed the Great Crash. The idea that the rise in the fragmentation of production across global value chains -vertical specialization -may be a deterrent against protectionism is underappreciated in the literature. Institutions also played a role in limiting the extent of protectionist responses. World Trade Organization discipline raises the cost of using trade policies for member countries and has proved to be a stable foundation for the open multilateral trading system that has been built over the past 50 years. Using trade and protection data for seven large emerging market countries that have a history of active use of trade policy, the influence of these and other factors on trade policy responses to the 2008 crisis are empirically examined. An instrumental variables strategy is used to identify their impact. Participation in global value chains is found to be a powerful economic factor determining trade policy responses. JEL codes: F13, F5, L52The contraction in output and collapse in trade that followed the 2008 financial crisis was comparable to what occurred in the early years of the Great Depression of 1930. Eichengreen and O'Rourke (2012, Figure 2) depict, in parallel, how far and how fast trade collapsed following the Great Depression and the

The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

Aberrant fibroblast growth factor 19 (FGF19) signaling mediated by its receptor, FGF receptor 4 (FGFR4), and coreceptor, klotho β (KLB), is a driver of hepatocellular carcinoma (HCC). Several potent FGFR4-selective inhibitors have been developed but have exhibited limited efficacy in HCC clinical trials. Here, by using HCC cell line models from the Cancer Cell Line Encyclopedia (CCLE) and the Liver Cancer Model Repository (LIMORE), we show that selective FGFR4 inactivation was not sufficient to inhibit cancer cell proliferation and tumor growth in FGF19-positive HCC. Moreover, genetic inactivation of KLB in these HCC cells resulted in a fitness defect more severe than that resulting from inactivation of FGFR4 . By a combination of biochemical and genetic approaches, we found that KLB associated with FGFR3 and FGFR4 to mediate the prosurvival functions of FGF19. KLB mutants defective in interacting with FGFR3 or FGFR4 could not support the growth or survival of HCC cells. Genome-wide CRISPR loss-of-function screening revealed that FGFR3 restricted the activity of FGFR4-selective inhibitors in inducing cell death; the pan-FGFR inhibitor erdafitinib displayed superior potency than FGFR4-selective inhibitors in suppressing the growth and survival of FGF19-positive HCC cells. Among FGF19-positive HCC cases from The Cancer Genome Atlas (TCGA), FGFR3 is prevalently coexpressed with FGFR4 and KLB, suggesting that FGFR redundancy may be a common mechanism underlying the de novo resistance to FGFR4 inhibitors. Our study provides a rationale for clinical testing of pan-FGFR inhibitors as a treatment strategy for FGF19-positive HCC.