The Fbxw7 (F-box/WD repeat–containing protein 7; also called CDC4, Sel10, Ago, and Fbw7) component of the SCF (Skp1/Cullin/F-box protein) E3 ubiquitin ligase complex acts as a tumor suppressor in several tissues and targets multiple transcriptional activators and protooncogenes for ubiquitin-mediated degradation. To understand Fbxw7 function in the murine intestine, in this study, we specifically deleted Fbxw7 in the murine gut using Villin-Cre (Fbxw7^ΔG). In wild-type mice, loss of Fbxw7 in the gut altered homeostasis of the intestinal epithelium, resulted in elevated Notch and c-Jun expression, and induced development of adenomas at 9–10 mo of age. In the context of APC (adenomatous polyposis coli) deficiency (Apc^Min/+ mice), loss of Fbxw7 accelerated intestinal tumorigenesis and death and promoted accumulation of β-catenin in adenomas at late but not early time points. At early time points, Fbxw7 mutant tumors showed accumulation of the DEK protooncogene. DEK expression promoted cell division and altered splicing of tropomyosin (TPM) RNA, which may also influence cell proliferation. DEK accumulation and altered TPM RNA splicing were also detected in FBXW7 mutant human colorectal tumor tissues. Given their reduced lifespan and increased incidence of intestinal tumors, Apc^Min/+Fbxw7^ΔG mice may be used for testing carcinogenicity and drug screening.

Carcinomas are complex heterocellular systems containing epithelial cancer cells, stromal fibroblasts, and multiple immune cell‐types. Cell‐cell communication between these tumor microenvironments (TME) and cells drives cancer progression and influences response to existing therapies. In order to provide better treatments for patients, we must understand how various cell‐types collaborate within the TME to drive cancer and consider the multiple signals present between and within different cancer types. To investigate how tissues function, we need a model to measure both how signals are transferred between cells and how that information is processed within cells. The interplay of collaboration between different cell‐types requires cell‐cell communication. This article aims to review the current in vitro and in vivo mono‐cellular and multi‐cellular cultures models of colorectal cancer (CRC), and to explore how they can be used for single‐cell multi‐omics approaches for isolating multiple types of molecules from a single‐cell required for cell‐cell communication to distinguish cancer cells from normal cells. Integrating the existing single‐cell signaling measurements and models, and through understanding the cell identity and how different cell types communicate, will help predict drug sensitivities in tumor cells and between‐ and within‐patients responses.

Wnt signalling is a crucial signalling pathway controlling intestinal homeostasis and cancer. We show here that the JNK MAP kinase pathway and one of its most important substrates, the AP‐1 transcription factor c‐Jun, modulates Wnt signalling strength in the intestine. Transgenic gut‐specific augmentation of JNK signalling stimulated progenitor cell proliferation and migration, resulting in increased villus length. In the crypt, c‐Jun protein was highly expressed in progenitor cells and the absence of c‐Jun resulted in decreased proliferation and villus length. In addition to several known c‐Jun/AP‐1 target genes, expression of Wnt target genes Axin2 and Lgr5 were stimulated by JNK activation, suggesting a cross talk of JNK to Wnt signalling. Expression of the Wnt pathway component TCF4 was controlled by JNK activity, and chromatin immunoprecipitation and reporter assays identified tcf4 as a direct c‐Jun target gene. Consequently, increased JNK activity accelerated tumourigenesis in a model of colorectal carcinogenesis. As c‐jun is a direct target of the TCF4/β‐catenin complex, the control of tcf4 expression by JNK/c‐Jun leads to a positive feedback loop that connects JNK and Wnt signalling. This mechanism regulates the physiological function of progenitor cells and oncogenic transformation.

The ERK MAPK signalling pathway is a highly conserved kinase cascade linking transmembrane receptors to downstream effector mechanisms. To investigate the function of ERK in neurons, a constitutively active form of MEK1 (caMEK1) was conditionally expressed in the murine brain, which resulted in ERK activation and caused spontaneous epileptic seizures. ERK activation stimulated phosphorylation of eukaryotic translation initiation factor 4E (eIF4E) and augmented NMDA receptor 2B (NR2B) protein levels. Pharmacological inhibition of NR2B function impaired synaptic facilitation in area cornus ammonicus region 3 (CA3) in acute hippocampal slices derived from caMEK1‐expressing mice and abrogated epilepsy in vivo . In addition, expression of caMEK1 caused phosphorylation of the transcription factor, cAMP response element‐binding protein (CREB) and increased transcription of ephrinB2 . EphrinB2 overexpression resulted in increased NR2B tyrosine phosphorylation, which was essential for caMEK1‐induced epilepsy in vivo , since conditional inactivation of ephrinB2 greatly reduced seizure frequency in caMEK1 transgenic mice. Therefore, our study identifies a mechanism of epileptogenesis that links MAP kinase to Eph/Ephrin and NMDA receptor signalling.