Background

Body mass index (BMI) has been implicated as a primary factor influencing cancer development. However, understanding the relationship between these two complex traits has been confounded by both environmental and genetic heterogeneity.

Methods

In order to gain insight into the genetic factors linking BMI and cancer, we performed chemical carcinogenesis on a genetically heterogeneous cohort of interspecific backcross mice ((Mus Spretus × FVB/N) F1 × FVB/N). Using this cohort, we performed quantitative trait loci (QTL) analysis to identify regions linked to BMI. We then performed an integrated analysis incorporating gene expression, sequence comparison between strains, and gene expression network analysis to identify candidate genes influencing both tumor development and BMI.

Results

Analysis of QTL linked to tumorigenesis and BMI identified several loci associated with both phenotypes. Exploring these loci in greater detail revealed a novel relationship between the Pannexin 3 gene (Panx3) and both BMI and tumorigenesis. Panx3 is positively associated with BMI and is strongly tied to a lipid metabolism gene expression network. Pre-treatment Panx3 gene expression levels in normal skin are associated with tumor susceptibility and inhibition of Panx function strongly influences inflammation.

Conclusions

These studies have identified several genetic loci that influence both BMI and carcinogenesis and implicate Panx3 as a candidate gene that links these phenotypes through its effects on inflammation and lipid metabolism.

Ptch1 is a key regulator of embryonic development, acting through the sonic hedgehog (SHH) signaling pathway. Ptch1 is best known as a tumor suppressor, as germline or somatic mutations in Ptch1 lead to the formation of skin basal cell carcinomas. Here we show that Ptch1 also acts as a lineage-dependent oncogene, as overexpression of Ptch1 in adult skin in K14Ptch(FVB) transgenic mice synergizes with chemically induced Hras mutations to promote squamous carcinoma development. These effects were not because of aberrant activation of SHH signaling by the K14Ptch(FVB) transgene, as developmental defects in the highest expressing transgenic lines were consistent with the inhibition of this pathway. Carcinomas from K14Ptch(FVB) transgenic mice had only a small number of nonproliferative Ptch1 transgene-positive cells, suggesting that the Ptch1 transgene is not required for tumor maintenance, but may have a critical role in cell-fate determination at the initiation stage.

Ptch1 is a key regulator of embryonic development, acting through the sonic hedgehog (SHH) signaling pathway. Ptch1 is best known as a tumor suppressor, as germline or somatic mutations in Ptch1 lead to the formation of skin basal cell carcinomas. Here we show that Ptch1 also acts as a lineage-dependent oncogene, as overexpression of Ptch1 in adult skin in K14Ptch(FVB) transgenic mice synergizes with chemically induced Hras mutations to promote squamous carcinoma development. These effects were not because of aberrant activation of SHH signaling by the K14Ptch(FVB) transgene, as developmental defects in the highest expressing transgenic lines were consistent with the inhibition of this pathway. Carcinomas from K14Ptch(FVB) transgenic mice had only a small number of nonproliferative Ptch1 transgene-positive cells, suggesting that the Ptch1 transgene is not required for tumor maintenance, but may have a critical role in cell-fate determination at the initiation stage.

Lung neuroendocrine (NE) tumors are a heterogeneous group of tumors arising from neuroendocrine cells that includes typical carcinoid, atypical carcinoid, small cell lung cancer (SCLC), and large cell NE cancer. The subtyping of NE tumors is based on the number of mitoses per high powered field and the presences of necrosis. However, the best diagnostic criteria to differentiate various subtypes of lung NE tumors remains controversial and few diagnostic markers distinguish typical and atypical carcinoid. In this study, we show that FAIM2, an inhibitory molecule in the Fas-apoptosis pathway, is significantly overexpressed in SCLC compared to non-small cell lung cancer. In addition, FAIM2 expression is significantly higher in atypical carcinoid than typical carcinoid. As atypical carcinoid has been shown to have worse clinical outcomes than typical carcinoid, our data suggests that FAIM2 may be a useful diagnostic marker for atypical carcinoid. Knockdown of FAIM2 expression increases Fas-induced apoptotic cell death in SCLC cells. Etoposide treatment combined with FAIM2 inhibition also shows modest but significant reduction of viable SCLC cells. Taken together, our results suggest that FAIM2 is a potential NE tumor marker with higher expression in atypical carcinoid and SCLC, and could be a new therapeutic target for SCLC.

BACKGROUND: Gremlin, a member of the Dan family of BMP antagonists, is a glycosylated extracellular protein. Previously Gremlin has been shown to play a role in dorsal-ventral patterning, in tissue remodeling, and recently in angiogenesis. Evidence has previously been presented showing both over- and under-expression of Gremlin in different tumor tissues. Here, we sought to quantify expression of Gremlin in cancers of the lung and performed in vitro experiments to check whether Gremlin promotes cell growth and proliferation. METHODOLOGY/PRINCIPAL FINDINGS: Expression of Gremlin in 161 matched tumor and normal lung cancer specimens is quantified by quantitative real-time PCR and protein level is measured by immunohistochemistry. GREM1 was transfected into lung fibroblast and epithelial cell lines to assess the impact of overexpression of Gremlin in vitro. RESULTS: Lung adenocarcinoma but not squamous cell carcinoma shows a significant increase in Gremlin expression by mRNA and protein level. Lung fibroblast and epithelial cell lines transfected with GREM1 show significantly increased cell proliferation. CONCLUSIONS/SIGNIFICANCE: Our data suggest that Gremlin acts in an oncogenic manner in lung adenocarcinoma and could hold promise as a new diagnostic marker or potential therapeutic target in lung AD or general thoracic malignancies.

How oncogenes modulate the self-renewal properties of cancer-initiating cells is incompletely understood. Activating KRAS and NRAS mutations are among the most common oncogenic lesions detected in human cancer, and occur in myeloproliferative disorders (MPDs) and leukemias. We investigated the effects of expressing oncogenic Kras(G12D) from its endogenous locus on the proliferation and tumor-initiating properties of murine hematopoietic stem and progenitor cells. MPD could be initiated by Kras(G12D) expression in a highly restricted population enriched for hematopoietic stem cells (HSCs), but not in common myeloid progenitors. Kras(G12D) HSCs demonstrated a marked in vivo competitive advantage over wild-type cells. Kras(G12D) expression also increased the fraction of proliferating HSCs and reduced the overall size of this compartment. Transplanted Kras(G12D) HSCs efficiently initiated acute T-lineage leukemia/lymphoma, which was associated with secondary Notch1 mutations in thymocytes. We conclude that MPD-initiating activity is restricted to the HSC compartment in Kras(G12D) mice, and that distinct self-renewing populations with cooperating mutations emerge during cancer progression.

The Aurora-A kinase gene is frequently amplified and/or overexpressed in a variety of human cancers, leading to major efforts to develop therapeutic agents targeting this pathway. Here, we show that Aurora-A is targeted for ubiquitination and subsequent degradation by the F-box protein FBXW7 in a process that is regulated by GSK3β. Using a series of truncated Aurora-A proteins and site-directed mutagenesis, we identified distinct FBXW7 and GSK3β-binding sites in Aurora-A. Mutation of critical residues in either site substantially disrupts degradation of Aurora-A. Furthermore, we show that loss of Pten results in the stabilization of Aurora-A by attenuating FBXW7-dependent degradation of Aurora-A through the AKT/GSK3β pathway. Moreover, radiation-induced tumor latency is significantly shortened in Fbxw7(+/-)Pten(+/-) mice as compared with either Fbxw7(+/-) or Pten(+/-) mice, indicating that Fbxw7 and Pten appear to cooperate in suppressing tumorigenesis. Our results establish a novel posttranslational regulatory network in which the Pten and Fbxw7 pathways appear to converge on the regulation of Aurora-A level.

Malignant pleural mesothelioma (MPM), a rare malignancy with a poor prognosis, is mainly caused by exposure to asbestos or other organic fibers, but the underlying genetic mechanism is not fully understood. Genetic alterations and causes for multiple primary cancer development including MPM are unknown. We used whole exome sequencing to identify somatic mutations in a patient with MPM and two additional primary cancers who had no evidence of venous, arterial, lymphovascular, or perineural invasion indicating dissemination of a primary lung cancer to the pleura. We found that the MPM had R282W, a key TP53 mutation, and genome-wide allelic loss or loss of heterozygosity, a distinct genomic alteration not previously described in MPM. We identified frequent inactivating SETDB1 mutations in this patient and in 68 additional MPM patients (mutation frequency: 10%, 7/69) by targeted deep sequencing. Our observations suggest the possibility of a new genetic mechanism in the development of either MPM or multiple primary cancers. The frequent SETDB1 inactivating mutations suggest there could be new diagnostic or therapeutic options for MPM.

The G-protein-coupled receptors LGR4, LGR5 and LGR6 are Wnt signaling mediators, but their functions in squamous cell carcinoma (SCC) are unclear. Using lineage tracing in Lgr5-EGFP-CreERT2/Rosa26-Tomato and Lgr6-EGFP-CreERT2/Rosa26-Tomato reporter mice, we demonstrate that Lgr6, but not Lgr5, acts as an epithelial stem cell marker in SCCs in vivo. We identify, by single-molecule in situ hybridization and cell sorting, rare cells positive for Lgr6 expression in immortalized keratinocytes and show that their frequency increases in advanced SCCs. Lgr6 expression is enriched in cells with stem cell characteristics, and Lgr6 downregulation in vivo causes increased epidermal proliferation with expanded lineage tracing from epidermal stem cells positive for Lgr6 expression. Surprisingly, mice with germline knockout of Lgr6 are predisposed to SCC development, through a mechanism that includes compensatory upregulation of Lgr5. These data provide a model for human patients with germline loss-of-function mutations in Wnt pathway genes, including RSPO1 or LGR4, who show increased susceptibility to squamous tumor development.