Gene fusions in gastrointestinal tract cancers.

Fusion genes have been identified in a wide array of human neoplasms including hematologic and solid tumors, including gastrointestinal tract neoplasia. A fusion gene is the product of parts of two genes that are joined together following a deletion, translocation, or chromosomal inversion. Together with single nucleotide variants, insertions, deletions, and amplification, fusion genes represent one of the key genomic mechanisms for tumor development. Detecting fusions in the clinic is accomplished by a variety of techniques including break-apart fluorescence in situ hybridization, reverse transcription-polymerase chain reaction, and next-generation sequencing. Some recurrent gene fusions have been successfully targeted by small molecule or monoclonal antibody therapies (ie targeted therapies), while others are used as biomarkers for diagnostic and prognostic purposes. The purpose of this review article is to discuss the clinical utility of detection of gene fusions in carcinomas and neoplasms arising primarily in the digestive system.

GPNMB methylation: a new marker of potentially carcinogenic colon lesions.

BACKGROUND: Epigenetic plays an important role in colorectal neoplasia process. There is a need to determine sound biomarkers of colorectal cancer (CRC) progression with clinical and therapeutic implications. Therefore, we aimed to examine the role and methylation status of Glyco Protein Non-Metastatic GPNM B (GPNMB) gene in normal, adenoma and CRC in African American (AA) patients. METHODS: The methylation status of 13 CpG sites (chr7: 23287345-23,287,426) in GPNMB gene's promoter, was analyzed by pyrosequencing in human CRC cell lines (HCT116, SW480, and HT29) and microdissected African American paraffin embedded samples (20 normal, 21 non-advanced adenoma (NA), 48 advanced adenoma (AD), and 20 cancer tissues. GPNMB expression was analyzed by immunohistochemistry (IHC) on tissue microarrays (TMA). Correlations between GPNMB methylation and expression with clinicopathological features were analyzed. GPNMB functional analysis was performed in triplicates using cell proliferation, migration and invasion assays in HCT116 colon cell line after stable transfection with a GPNMB-cDNA expression vector. RESULTS: GPNMB methylation was lower in normal mucosa compared to CRC samples (1/20 [5%] vs. 18/20 [90%]; P < 0.001). AD also had a significantly higher GPNMB methylation frequency than normal colon samples (42/48 [88%] vs 1/20 [5%]; P < 0.001). GPNMB was more frequently methylated in AD than in matched normal mucosa from three patients (3/3 [100%] vs 1/3 [33.3%]; P < 0.001). The frequency of GPNMB methylation in NA differed significantly from that in the normal mucosa (16/21 [76%] vs 1/20 [5%]; P = 0.008). There was statistically significant correlation of higher methylation at advanced stages and lower methylation at stage 1 CRCs (P < 0.05). In agreement with these findings, GPNMB protein expression decreased in CRC tissues compared with AD and NA colon mucosa (p < 0.05). GPNMB overexpression in HCT116 colon cancer cell line decreased cell proliferation [(24 h, P = 0.02), (48 h, P < 0.001, 72 h, P = 0.007)], invasion (p < 0.05) and migration (p > 0.05) compared to the mock-transfected cells. CONCLUSION: Our data indicate a high methylation profile leading to a lower GPNMB expression in adenoma and CRC samples. The functional analysis established GPNMB as a potential tumor suppressor gene. As such, GPNMB might be useful as a biomarker of adenomas with high carcinogenic potential.

Identification of novel mutations by exome sequencing in African American colorectal cancer patients.

BACKGROUND: The purpose of this study was to identify genome-wide single nucleotide variants and mutations in African American patients with colorectal cancer (CRC). There is a need of such studies in African Americans, because they display a higher incidence of aggressive CRC tumors. METHODS: We performed whole exome sequencing (WES) on DNA from 12 normal/tumor pairs of African American CRC patient tissues. Data analysis was performed using the software package GATK (Genome Analysis Tool Kit). Normative population databases (eg, 1000 Genomes SNP database, dbSNP, and HapMap) were used for comparison. Variants were annotated using analysis of variance and were validated via Sanger sequencing. RESULTS: We identified somatic mutations in genes that are known targets in CRC such as APC, BRAF, KRAS, and PIK3CA. We detected novel alterations in the Wnt pathway gene, APC, within its exon 15, of which mutations are highly associated with CRC. CONCLUSIONS: This WES study in African American patients with CRC provides insight into the identification of novel somatic mutations in APC. Our data suggest an association between specific mutations in the Wnt signaling pathway and an increased risk of CRC. The analysis of the pathogenicity of these novel variants may shed light on the aggressive nature of CRC in African Americans.

EGFR mediates activation of RET in lung adenocarcinoma with neuroendocrine differentiation characterized by ASCL1 expression.

Achaete-scute homolog 1 (ASCL1) is a neuroendocrine transcription factor specifically expressed in 10-20% of lung adenocarcinomas (AD) with neuroendocrine (NE) differentiation (NED). ASCL1 functions as an upstream regulator of the RET oncogene in AD with high ASCL1 expression (A+AD). RET is a receptor tyrosine kinase with two main human isoforms; RET9 (short) and RET51 (long). We found that elevated expression of RET51 associated mRNA was highly predictive of poor survival in stage-1 A+AD (p=0.0057). Functional studies highlighted the role of RET in promoting invasive properties of A+AD cells. Further, A+AD cells demonstrated close to 10 fold more sensitivity to epidermal growth factor receptor (EGFR) inhibitors, including gefitinib, than AD cells with low ASCL1 expression. Treatment with EGF robustly induced phosphorylation of RET at Tyr-905 in A+AD cells with wild type EGFR. This phosphorylation was blocked by gefitinib and by siRNA-EGFR. Immunoprecipitation experiments found EGFR in a complex with RET in the presence of EGF and suggested that RET51 was the predominant RET isoform in the complex. In the microarray datasets of stage-1 and all stages of A+AD, high levels of EGFR and RET RNA were significantly associated with poor overall survival (p < 0.01 in both analyses). These results implicate EGFR as a key regulator of RET activation in A+AD and suggest that EGFR inhibitors may be therapeutic in patients with A+AD tumors even in the absence of an EGFR or RET mutation.

Toward a comprehensive and systematic methylome signature in colorectal cancers.

CpG Island Methylator Phenotype (CIMP) is one of the underlying mechanisms in colorectal cancer (CRC). This study aimed to define a methylome signature in CRC through a methylation microarray analysis and a compilation of promising CIMP markers from the literature. Illumina HumanMethylation27 (IHM27) array data was generated and analyzed based on statistical differences in methylation data (1st approach) or based on overall differences in methylation percentages using lower 95% CI (2nd approach). Pyrosequencing was performed for the validation of nine genes. A meta-analysis was used to identify CIMP and non-CIMP markers that were hypermethylated in CRC but did not yet make it to the CIMP genes' list. Our 1st approach for array data analysis demonstrated the limitations in selecting genes for further validation, highlighting the need for the 2nd bioinformatics approach to adequately select genes with differential aberrant methylation. A more comprehensive list, which included non-CIMP genes, such as APC, EVL, CD109, PTEN, TWIST1, DCC, PTPRD, SFRP1, ICAM5, RASSF1A, EYA4, 30ST2, LAMA1, KCNQ5, ADHEF1, and TFPI2, was established. Array data are useful to categorize and cluster colonic lesions based on their global methylation profiles; however, its usefulness in identifying robust methylation markers is limited and rely on the data analysis method. We have identified 16 non-CIMP-panel genes for which we provide rationale for inclusion in a more comprehensive characterization of CIMP+ CRCs. The identification of a definitive list for methylome specific genes in CRC will contribute to better clinical management of CRC patients.