Jennifer L. Cotton

TRIB2 Acts Downstream of Wnt/TCF in Liver Cancer Cells to Regulate YAP and C/EBPα Function

Dysregulation of Wnt signaling is closely associated with human liver tumorigenesis. However, liver cancer-specific Wnt transcriptional programs and downstream effectors remain poorly understood. Here, we identify tribbles homolog 2 (TRIB2) as a direct target of Wnt/TCF in liver cancer and demonstrate that transcription of Wnt target genes, including TRIB2, is coordinated by the TCF and FoxA transcription factors in liver cancer cells. We show that Wnt-TRIB2 activation is critical for cancer cell survival and transformation. Mechanistically, TRIB2 promotes protein stabilization of the YAP transcription coactivator through interaction with the βTrCP ubiquitin ligase. Furthermore, we find that TRIB2 relieves the liver tumor suppressor protein C/EBPα-mediated inhibition of YAP/TEAD transcriptional activation in liver cancer cells. Altogether, our study uncovers a regulatory mechanism underlying liver cancer-specific Wnt transcriptional output, and suggests that TRIB2 functions as a signaling nexus to integrate the Wnt/β-catenin, Hippo/YAP, and C/EBPα pathways in cancer cells.

The activity of Gli transcription factors is essential for Kras-induced pancreatic tumorigenesis

Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive human malignancies, is thought to be initiated by KRAS activation. Here we find that transcriptional activation mediated by the Gli family of transcription factors, although dispensable for pancreatic development, is required for Kras-induced proliferation and survival in primary pancreatic epithelial cells in culture and for Kras-driven pancreatic intraepithelial neoplasia and PDAC formation in vivo. Further, ectopic Gli1 activation in the mouse pancreas accelerates Kras-driven tumor formation, underscoring the importance of Gli transcription factors in pancreatic tumorigenesis. Interestingly, we demonstrate Gli-regulated I-kappa-B kinase epsilon (IKBKE) and NF-κB activity in pancreatic cancer cells and show that this activity is a critical downstream mediator for Gli-dependent PDAC cell transformation and survival. Together, these studies demonstrate the requirement for Gli in Kras-dependent pancreatic epithelial transformation, suggest a mechanism of Gli-NF-κB oncogenic activation, and provide genetic evidence supporting the therapeutic targeting of Gli activity in pancreatic cancer.

The Conserved Misshapen-Warts-Yorkie Pathway Acts in Enteroblasts to Regulate Intestinal Stem Cells in Drosophila

Similar to the mammalian intestine, the Drosophila adult midgut has resident stem cells that support growth and regeneration. How the niche regulates intestinal stem cell activity in both mammals and flies is not well understood. Here, we show that the conserved germinal center protein kinase Misshapen restricts intestinal stem cell division by repressing the expression of the JAK-STAT pathway ligand Upd3 in differentiating enteroblasts. Misshapen, a distant relative to the prototypic Warts activating kinase Hippo, interacts with and activates Warts to negatively regulate the activity of Yorkie and the expression of Upd3. The mammalian Misshapen homolog MAP4K4 similarly interacts with LATS (Warts homolog) and promotes inhibition of YAP (Yorkie homolog). Together, this work reveals that the Misshapen-Warts-Yorkie pathway acts in enteroblasts to control niche signaling to intestinal stem cells. These findings also provide a model in which to study requirements for MAP4K4-related kinases in MST1/2-independent regulation of LATS and YAP.

Tead and AP1 Coordinate Transcription and Motility

The Tead family transcription factors are the major intracellular mediators of the Hippo-Yap pathway. Despite the importance of Hippo signaling in tumorigenesis, Tead-dependent downstream oncogenic programs and target genes in cancer cells remain poorly understood. Here, we characterize Tead4-mediated transcriptional networks in a diverse range of cancer cells, including neuroblastoma, colorectal, lung, and endometrial carcinomas. By intersecting genome-wide chromatin occupancy analyses of Tead4, JunD, and Fra1/2, we find that Tead4 cooperates with AP1 transcription factors to coordinate target gene transcription. We find that Tead-AP1 interaction is JNK independent but engages the SRC1-3 co-activators to promote downstream transcription. Furthermore, we show that Tead-AP1 cooperation regulates the activity of the Dock-Rac/CDC42 module and drives the expression of a unique core set of target genes, thereby directing cell migration and invasion. Together, our data unveil a critical regulatory mechanism underlying Tead- and AP1-controlled transcriptional and functional outputs in cancer cells.

Riboflavin Is an Active Redox Cofactor in the Na+-pumping NADH:Quinone Oxidoreductase (Na+-NQR) from Vibrio cholerae

Here we present new evidence that riboflavin is present as one of four flavins in Na+-NQR. In particular, we present conclusive evidence that the source of the neutral radical is not one of the FMNs and that riboflavin is the center that gives rise to the neutral flavosemiquinone. The riboflavin is a bona fide redox cofactor and is likely to be the last redox carrier of the enzyme, from which electrons are donated to quinone. We have constructed a double mutant that lacks both covalently bound FMN cofactors (NqrB-T236Y/NqrC-T225Y) and have studied this mutant together with the two single mutants (NqrB-T236Y and NqrC-T225Y) and a mutant that lacks the noncovalently bound FAD in NqrF (NqrF-S246A). The double mutant contains riboflavin and FAD in a 0.6:1 ratio, as the only flavins in the enzyme; noncovalently bound flavins were detected. In the oxidized form, the double mutant exhibits an EPR signal consistent with a neutral flavosemiquinone radical, which is abolished on reduction of the enzyme. The same radical can be observed in the FAD deletion mutant. Furthermore, when the oxidized enzyme reacts with ubiquinol (the reduced form of the usual electron acceptor) in a process that reverses the physiological direction of the electron flow, a single kinetic phase is observed. The kinetic difference spectrum of this process is consistent with one-electron reduction of a neutral flavosemiquinone. The presence of riboflavin in the role of a redox cofactor is thus far unique to Na+-NQR.

Specific Requirement of Gli Transcription Factors in Hedgehog-mediated Intestinal Development

Background: Hedgehog signaling plays important roles during intestinal development. Results: Mesenchymal Gli2 activation, but not Gli3 removal, rescued Hedgehog pathway defects. Screen identified small leucine-rich glycoproteins (SLRPs) downstream of Hedgehog in the gut. Conclusion: Hedgehog activity is mediated by Gli2 and involves SLRP regulation in the developing intestine. Significance: This study uncovers novel genetic and molecular mechanisms underlying Hedgehog function in intestinal development. Hedgehog (Hh) signaling is involved in multiple aspects of embryonic gut development, including mesenchymal growth and smooth muscle differentiation. The Gli family transcription factors is thought to collectively mediate Hh signaling in mammals. However, the function of different Gli proteins in gut development remains uncharacterized. Here, we genetically dissect the contribution of Gli transcriptional activation and de-repression in intestinal growth and patterning. We find that removal of the Gli3 repressor is dispensable for intestinal development and does not play a major role in Hh-controlled gut development. However, Gli2 activation is able to fully rescue the Smoothened (Smo)-null intestinal phenotype, suggesting that the Gli2 transcription factor is the main effector for Hh signaling in the intestine. To understand further the molecular mechanism underlying Hh/Gli function in the developing gut, we identify a subset of small leucine-rich glycoproteins (SLRPs) that may function downstream of Hh signaling in the mesenchyme. We show that osteoglycin, a SLRP, inhibits Hh-induced differentiation toward the smooth muscle lineage in C3H10T1/2 pluripotent mesenchymal cells. Taken together, our study reveals, for the first time, the distinct roles of Gli proteins in intestine development and suggests SLRPs as novel regulators of smooth muscle cell differentiation.

Distinct cellular origin and genetic requirement of Hedgehog-Gli in postnatal rhabdomyosarcoma genesis.

Dysregulation of the Hedgehog (Hh)-Gli signaling pathway is implicated in a variety of human cancers, including basal cell carcinoma (BCC), medulloblastoma (MB) and embryonal rhabdhomyosarcoma (eRMS), three principle tumors associated with human Gorlin syndrome. However, the cells of origin of these tumors, including eRMS, remain poorly understood. In this study, we explore the cell populations that give rise to Hh-related tumors by specifically activating Smoothened (Smo) in both Hh-producing and -responsive cell lineages in postnatal mice. Interestingly, we find that unlike BCC and MB, eRMS originates from the stem/progenitor populations that do not normally receive active Hh signaling. Furthermore, we find that the myogenic lineage in postnatal mice is largely Hh quiescent and that Pax7-expressing muscle satellite cells are not able to give rise to eRMS upon Smo or Gli1/2 overactivation in vivo, suggesting that Hh-induced skeletal muscle eRMS arises from Hh/Gli quiescent non-myogenic cells. In addition, using the Gli1 null allele and a Gli3 repressor allele, we reveal a specific genetic requirement for Gli proteins in Hh-induced eRMS formation and provide molecular evidence for the involvement of Sox4/11 in eRMS cell survival and differentiation.

Abstract B06: Complex requirement of YAP and TAZ in gastrointestinal development and tumorigenesis

YAP and TAZ are the major intracellular mediators of Hippo signaling in mammals; however, the precise function of YAP/TAZ in gastrointestinal development and tumorigenesis remains poorly understood. By specific removal of YAP/TAZ from the developing endoderm and gastrointestinal tract, we find that YAP/TAZ are dispensable for Wnt signal transduction and normal gastrointestinal epithelial differentiation, but act as the direct TCF4 targets and downstream effectors during epithelial transformation. Surprisingly, our loss- and gain-of-function genetic analyses identify an essential role for YAP/TAZ in the gastrointestinal mesenchyme as a molecular switch to coordinate growth and differentiation. We find that YAP/TAZ are required for the expansion of the primitive progenitor populations critical for mesenchymal growth. However, persistent YAP activation inhibits the induction of the smooth muscle lineage, and YAP/TAZ down-regulation during later development is essential for Hedgehog signaling-induced differentiation of smooth muscle cells. Taken together, our studies uncover a complex requirement of YAP/TAZ in the gastrointestinal tract and demonstrate the functional interplays among key signaling pathways during gastrointestinal development and tumorigenesis. Citation Format: Jennifer L. Cotton, Qi Li, Lifang Ma, Tony Ip, Randy Johnson, Junhao Mao. Complex requirement of YAP and TAZ in gastrointestinal development and tumorigenesis. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr B06.

Abstract B07: Tead and AP1 coordinate transcription and motility in cancer cells

The Tead family transcription factors are the major mediators of the Hippo-Yap pathway. Although misregulation of Hippo signaling has been implicated in many human cancers, Tead dependent downstream transcriptional programs in cancer cells remain poorly understood. Here we characterize Tead4-mediated transcriptional networks in diverse cancer cells, including neuroblastoma, colorectal, lung, and endometrial carcinomas. By intersecting genome-wide chromatin occupancy analyses of Tead4, JunD, and Fra1/2, we find that Tead4 cooperates with AP1 factors to coordinate target gene transcription. We find that the interaction of AP1 and Tead4 is JNK independent, but engages the SRC coactivators to promote downstream transcription. Furthermore we show that Tead and AP1 drive the expression of a unique core set of target genes to direct cell motility and invasion. Together, our data unveil a critical regulatory mechanism coordinating AP1 and Tead -controlled transcriptional and functional output in cancer cells. Citation Format: Xiangfan Liu, Huapeng Li, Mihir Rajurkar, Jennifer Cotton, Arthur Mercurio, Roger Davis, Junhao Mao. Tead and AP1 coordinate transcription and motility in cancer cells. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr B07.

Abstract 98: A novel mouse model for intestinal serrated polyposis

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Serrated polyps have recently been proposed to comprise at least 30% of the origins of human colorectal cancer (CRC). Unlike adenomatous polyps, which are initiated by APC/β-catenin mutations, the genetic and molecular mechanisms underlying the serrated pathway that leads to serrated polyp initiation and progression remain poorly understood. Here we describe a novel genetically modified mouse model of serrated polyposis via conditional activation of SMAD7, an inhibitory SMAD protein, in the intestinal epithelia. We show that SMAD7 activation is sufficient to drive serrated polyp initiation and progression to aggressive adenocarcinoma in both mouse intestine and colon. Mechanistically, we find that SMAD7-induced foci formation in non-transformed intestinal epithelial cells in vitro and serrated polyposis in vivo are Wnt/β-catenin independent. Furthermore, we find that, in addition to its regulation of TGFβ/BMP pathway, SMAD7 interacts with BRAF/MAPK signaling to regulate serrated polyposis. Taken together, our studies implicate for the first time the involvement of SMAD7 in serrated polyposis and reveal a potential novel molecular mechanism underlying the serrated polyp pathway. Citation Format: Jennifer Cotton, He Huang, Mihir Rajurkar, Junhao Mao. A novel mouse model for intestinal serrated polyposis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 98. doi:10.1158/1538-7445.AM2014-98