Chen et al. Page 468

Despite previous assumptions that constitutively high Wnt signaling promotes colorectal cancer in each stage of disease, recent studies have demonstrated that reduced Wnt signaling is associated with colorectal cancer invasiveness and poor prognoses. However, little work has been done to elucidate how diminished Wnt signaling underlies aggressive colorectal cancer phenotypes. Chen and colleagues used genetic manipulation strategies and orthotopic mouse models to show that abrogating Wnt signaling increases colorectal cancer invasiveness and decreases immune responsiveness in vivo. Disrupting Wnt signaling by targeting Wnt coreceptor LDL receptor-related protein 6 (LRP6) with CRISPR/Cas9 or transducing a dominant negative version of Wnt transcriptional effector lymphoid enhancer binding factor 1 (LEF1) increases tumor submucosal invasion and dissemination in mice. Using RNA-Seq, the authors revealed that reducing Wnt signaling elevates expression of markers associated with stemness and a mesenchymal phenotype, while repressing expression of immune-stimulatory molecules and collagens. The authors used TCGA data to demonstrate that the low Wnt signaling expression profile corresponds with poor survival in colorectal cancer patients, underscoring the potential clinical relevance of dampened Wnt signaling in colorectal cancer progression.

Zhang et al. Page 350

Cholangiocarcinoma (CCA) is an aggressive biliary tract cancer for which effective therapeutics are lacking. Prostaglandin E2 (PGE2)-mediated inflammation is a critical component of CCA carcinogenesis and progression. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) chemically modifies and inactivates PGE2, but its expression is often diminished in CCA. In their work, Zhang and colleagues leveraged public data to show that expression of histone methyltransferase G9a negatively correlates with 15-PGDH expression. The authors validated the G9a-15-PGDH relationship in a mouse model of CCA in which the Notch intracellular domain and constitutively active Akt are expressed via hydrodynamic injection of sleeping beauty transposase-based plasmids. shRNA-mediated G9a silencing increases 15-PGDH expression in CCA cell lines, limiting cell proliferation in vitro and tumor growth in vivo. ChIP assays demonstrated that G9a is recruited to the 15-PGDH promoter by the Myc/Max/E-box complex, which prevents signal transducer and activator of transcription 4 (STAT4) from binding the promoter and inducing 15-PGDH expression. The work presented elucidates a previously unknown mechanism underlying CCA development and progression and reveals a novel potential target for CCA therapeutic strategies.

Cho et al. Page 412

Neurofibromatosis type 2 is characterized by growth of benign nervous system tumors, such as schwannomas, which can lead to deafness, brain stem compression, and death. Neurofibromatosis type 2 is caused by mutations in tumor suppressor gene NF2. Previously, Cho and colleagues demonstrated that NF2 loss promotes elevated TβR1 signaling, resulting in phosphorylation and degradation of tumor suppressor Raf kinase inhibitor protein (RKIP). While TGF-β inhibitors halt schwannoma growth, they are not ideal therapeutics given schwannomas occur around adolescence and TGF-β is required for development. Here, Cho and colleagues developed a novel TβR1 inhibitor, Nf18001, that abrogates TβR1-mediated RKIP degradation while maintaining canonical TGF-β signaling. The authors used human and mouse schwannoma cell lines to demonstrate that Nf18001 disrupts TβR1-RKIP interactions to sustain RKIP expression and lower NF2-mutant cell viability while not influencing normal fibroblast survival. Nf18001 arrests cell cycle progression in schwannoma cells, and augments Schwann cell differentiation marker expression while diminishing expression of markers associated with cell stemness. Nf18001 also displayed efficacy in a schwannoma allograft mouse model, where treatment slowed tumor growth.

Zhou et al. Page 456

The pro-tumorigenic role of signal transducer and activator of transcription 3 (STAT3) in multiple myeloma has been established, but therapeutically targeting STAT3 has proven challenging. Similarly, given its canonical role in DNA damage repair, checkpoint kinase 1 (Chk1) inhibition has been tested in anti-cancer therapeutic regimens, but with ambiguous results. In their study, Zhou and colleagues employed a gene expression array to demonstrate that Chk1 inhibition diminishes expression of oncogenic STAT3 target genes in multiple myeloma cells, suggesting Chk1 inhibition may also effectively inhibit STAT3 activity. Subsequent work showed that Chk1 directly binds to STAT3 and phosphorylates it at tyrosine 705, enabling STAT3 dimerization and DNA binding. Chk1 inhibition — pharmacologically and via shRNA silencing — diminishes STAT3 tyrosine 705 phosphorylation and inhibits STAT3 DNA binding, reducing expression of STAT3 transcriptional targets. Chk1 inhibition abrogates STAT3 tyrosine 705 phosphorylation in IL-6–dependent, -independent, and bortezomib-resistant cells, as well as in patient primary myeloma mononuclear cells and multiple myeloma cells implanted into mice, suggesting Chk1 inhibition may provide therapeutic efficacy against multiple myeloma through a STAT3-related mechanism.