When oncogenes do not cause cancer

Environmental cues, not oncogene-induced senescence, may stop melanocytes with an activating mutation in the BRAF gene from turning into melanoma.

Molecular drivers of tumor progression in microsatellite stable APC mutation-negative colorectal cancers

The tumor suppressor gene adenomatous polyposis coli (APC) is the initiating mutation in approximately 80% of all colorectal cancers (CRC), underscoring the importance of aberrant regulation of intracellular WNT signaling in CRC development. Recent studies have found that early-onset CRC exhibits an increased proportion of tumors lacking an APC mutation. We set out to identify mechanisms underlying APC mutation-negative (APCmut–) CRCs. We analyzed data from The Cancer Genome Atlas to compare clinical phenotypes, somatic mutations, copy number variations, gene fusions, RNA expression, and DNA methylation profiles between APCmut– and APC mutation-positive (APCmut+) microsatellite stable CRCs. Transcriptionally, APCmut– CRCs clustered into two approximately equal groups. Cluster One was associated with enhanced mitochondrial activation. Cluster Two was strikingly associated with genetic inactivation or decreased RNA expression of the WNT antagonist RNF43, increased expression of the WNT agonist RSPO3, activating mutation of BRAF, or increased methylation and decreased expression of AXIN2. APCmut– CRCs exhibited evidence of increased immune cell infiltration, with significant correlation between M2 macrophages and RSPO3. APCmut– CRCs comprise two groups of tumors characterized by enhanced mitochondrial activation or increased sensitivity to extracellular WNT, suggesting that they could be respectively susceptible to inhibition of these pathways.

Gut-associated cGMP mediates colitis and dysbiosis in a mouse model of an activating mutation in GUCY2C

Activating mutations in receptor guanylyl cyclase C (GC-C), the target of gastrointestinal peptide hormones guanylin and uroguanylin, and bacterial heat-stable enterotoxins cause early-onset diarrhea and chronic inflammatory bowel disease (IBD). GC-C regulates ion and fluid secretion in the gut via cGMP production and activation of cGMP-dependent protein kinase II. We characterize a novel mouse model harboring an activating mutation in Gucy2c equivalent to that seen in an affected Norwegian family. Mutant mice demonstrated elevated intestinal cGMP levels and enhanced fecal water and sodium content. Basal and linaclotide-mediated small intestinal transit was higher in mutant mice, and they were more susceptible to DSS-induced colitis. Fecal microbiome and gene expression analyses of colonic tissue revealed dysbiosis, up-regulation of IFN-stimulated genes, and misregulation of genes associated with human IBD and animal models of colitis. This novel mouse model thus provides molecular insights into the multiple roles of intestinal epithelial cell cGMP, which culminate in dysbiosis and the induction of inflammation in the gut.

Molecular Drivers of Tumor Progression in Microsatellite Stable APC Mutation-Negative Colorectal Cancers

ABSTRACTBackgroundThe tumor suppressor gene adenomatous polyposis coli (APC) is the initiating mutation in approximately 80% of all colorectal cancers (CRC), underscoring the importance of aberrant regulation of intracellular WNT signaling in CRC development. Recent studies have found that early-onset CRC exhibits an increased proportion of tumors lacking an APC mutation. We set out to identify mechanisms underlying APC mutation-negative (APCmut–) CRCs.MethodsWe analyzed data from The Cancer Genome Atlas to compare clinical phenotypes, somatic mutations, copy number variations, gene fusions, RNA expression, and DNA methylation profiles between APCmut– and APC mutation-positive (APCmut+) microsatellite stable CRCs.ResultsTranscriptionally, APCmut– CRCs clustered into two approximately equal groups. Cluster One was associated with enhanced mitochondrial activation. Cluster Two was strikingly associated with genetic inactivation or decreased RNA expression of the WNT antagonist RNF43, increased expression of the WNT agonist RSPO3, activating mutation of BRAF, or increased methylation and decreased expression of AXIN2. APCmut– CRCs exhibited evidence of increased immune cell infiltration, with significant correlation between M2 macrophages and RSPO3.ConclusionsAPCmut– CRCs comprise two groups of tumors characterized by enhanced mitochondrial activation or increased sensitivity to extracellular WNT, suggesting that they could be respectively susceptible to inhibition of these pathways.

Activation of the viral sensor oligoadenylate synthetase 2 (Oas2) prevents pregnancy-driven mammary cancer metastases

BackgroundThe interferon response can influence the primary and metastatic activity of breast cancers and can interact with checkpoint immunotherapy to modulate its effects. Using N-ethyl-N-nitrosourea mutagenesis we found a mouse with an activating mutation in oligoadenylate synthetase 2 ( Oas2 ), a sensor of viral double stranded RNA, that resulted in an interferon response and prevented lactation in otherwise healthy mice. MethodsTo determine if activation of Oas2 could alter the course of mammary cancer we combined the Oas2 mutation with the MMTV-PyMT oncogene model of breast cancer and examined disease progression and the effects of checkpoint immunotherapy using Kaplan-Meier survival analysis with immunohistochemistry and flow cytometry. ResultsOas2 mutation prevented pregnancy from increasing metastases to lung. Checkpoint immunotherapy with antibodies against programmed death-ligand 1 (PD-L1) was more effective when the Oas2 mutation was present. ConclusionsThese data establish OAS2 as a therapeutic target for agents designed to reduce metastases and increase the effectiveness of checkpoint immunotherapy in cases of pregnancy-associated breast cancer and outside of pregnancy in cases showing the lactation and involution-mimicry phenotypes.

Multiple Primary Intracranial and Spinal Juvenile Xanthogranuloma: A Case Report

Juvenile Xanthogranuloma (JXG) is a rare histiocytic disorder that belongs to the non-Langerhans cell histiocytosis family. It commonly occurs in the skin of young children, particularly the head and neck region. Occasional cases with extracutaneous involvement have been described. However, involvement of the central nervous system without cutaneous lesions is extremely rare. We present a case of an 11-year-old male child with multiple intracranial and spinal JXGs. At 30 months follow up, after administration of chemotherapy, the patient had passed away. The broad clinical spectrum of JXG and the morphological resemblance to other histiocytic lesions prompt a cautious approach for the diagnosis. Immunohistochemically, those lesions were positive for CD68 and negative for S100 and CD1a. A revised classification for histiocytosis was recently proposed, based on the underlying molecular characteristics. The diagnosis of extracutaneous or disseminated JXG with MAPK-activating mutation or ALK translocations was considered as Erdheim-Chester disease. However, our study did not fit into the proposed classification due to the absence of BRAF-V600E gene mutation and ALK gene rearrangement. Chemotherapy with or without radiotherapy has been suggested as treatment options for unresectable central nervous system lesions.

The Biology of Classic Hairy Cell Leukemia

Classic hairy cell leukemia (HCL) is a rare mature B-cell malignancy associated with pancytopenia and infectious complications due to progressive infiltration of the bone marrow and spleen. Despite tremendous therapeutic advances achieved with the implementation of purine analogues such as cladribine into clinical practice, the culprit biologic alterations driving this fascinating hematologic disease have long stayed concealed. Nearly 10 years ago, BRAF V600E was finally identified as a key activating mutation detectable in almost all HCL patients and throughout the entire course of the disease. However, additional oncogenic biologic features seem mandatory to enable HCL transformation, an open issue still under active investigation. This review summarizes the current understanding of key pathogenic mechanisms implicated in HCL and discusses major hurdles to overcome in the context of other BRAF-mutated malignancies.