Receptor tyrosine kinase fusions act as a significant alternative driver of the serrated pathway in colorectal cancer development

Serrated polyps are a clinically and molecularly heterogeneous group of lesions that can contribute to the development of colorectal cancers (CRCs). However, the molecular mechanism underlying the development of serrated lesions is still not well understood. Here, we combined multiple approaches to analyze the genetic alterations in 86 colorectal adenomas (including 35 sessile serrated lesions, 15 traditional adenomas, and 36 conventional adenomatous polyps). We also investigated the in vitro and in vivo oncogenic properties of a novel variant of the NCOA4-RET fusion gene. Molecular profiling revealed that sessile serrated lesions and traditional serrated adenomas have distinct clinicopathological and molecular features. Moreover, we identified receptor tyrosine kinase translocations exclusively in sessile serrated lesions (17%), and the observation was validated in a separate cohort of 34 sessile serrated lesions (15%). The kinase fusions as well as the BRAF and KRAS mutations were mutually exclusive to each other. Ectopic expression of a novel variant of the NCOA4-RET fusion gene promoted cell proliferation in vitro and in vivo, and the proliferation was significantly suppressed by RET kinase inhibitors. All of these underscored the importance of mitogen-activated protein kinase (MAPK) pathway activation in the serrated pathway of colorectal tumorigenesis. In addition, we demonstrated that the kinase fusion may occur early in the precursor lesion and subsequent loss of TP53 may drives the transformation to carcinoma during serrated tumorigenesis. In conclusion, we identified kinase fusions as a significant alternative driver of the serrated pathway in colorectal cancer development, and detecting their presence may serve as a biomarker for the diagnosis of sessile serrated lesions. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Correlative Analysis of DNA Methyltransferase Expression and Promoter Hypermethylation of Tumor Suppressor Genes in Hepatocellular Carcinoma

BACKGROUND

Promoter hypermethylation of tumor suppressor genes (TSGs) is a common phenomenon in liver carcinogenesis, although the controlling mechanism remains unclear.

MATERIALS AND METHODS

The mRNA expression of DNA methyltransferases (DNMT1, 2, 3a, 3b and splice variants 3b3 and 3b4) and methyl-CpG binding protein (MBD2) were quantitated in 51 liver specimens (41 hepatocellular carcinoma (HCC), 1 cholangiocarcinoma, 1 macroregenerative nodule and 8 HCC cell lines) and the expression levels were correlated with the promoter methylation status of 14 TSG, including APC, RASSF1A, SOCS-1, GSTP1, E-cadherin, p14, p15, p16, DAP-kinase, HIC1, MGMT, TIMP-3, hMLH1 and HLTF.

RESULTS

Up-regulations of DNMT1, DNMT2, DNMT3a, DNMT3b4 and MBD2 were suggested in more than 40% of the cases. In particular, the overexpression of DNMT3b and the splice variant DNMT3b3 were identified in as many as 91% and 97.8% of cases, respectively. Using methylation-specific PCR, the most frequently methylated TSGs were APC (90.2%), RASSF1A (86.3%), SOC-1 (74.5%), GSTP1 (72.5%), E-cadherin (64.7%) and p16 (58%). Statistical correlations did not suggest the DNMTs and MBD2 expressions in association with cumulative methylated index in individual cases, but increased expression levels of DNMT2 and DNMT3a showed significant association with the hypermethylation of GSTP1 (p=0.014) and DAP-kinase (p=0.006), respectively. Furthermore, the analysis with clinicopathological data indicated aberrant DAP-kinase methylation was significantly associated with advanced stage T3/T4 HCC tumors (p=0.032) and that p16 hypermethylation was distinct more prevalent in tumors arising from a cirrhotic background (p=0.005).

CONCLUSION

Our study indicated that DNMT deregulations are common in liver cancers and the existence of a relationship between DNMT2 and DNMT3a overexpression and promoter hypermethylation of candidate tumor suppressor genes in HCC.

Constitutional activation of IL-6-mediated JAK/STAT pathway through hypermethylation of SOCS-1 in human gastric cancer cell line

The interleukin-mediated Janus kinase (JAK)/STAT pathway plays a crucial role in carcinogenesis. Recently, increased STAT3 activity was found in hepatocellular carcinoma and multiple myeloma in which there was silencing of SOCS-1 (suppressor of cytokine signalling-1) by gene promoter hypermethylation. We investigated the expression level of interleukin-6 (IL-6) and SOCS-1 in gastric cancer cell lines. Expression of SOCS-1 correlated with IL-6 level in most of the cell lines, except for AGS cells in which SOCS-1 was absent despite a high level of IL-6 production. Methylation analysis by methylation-specific polymerase chain reaction and bisulphite sequencing revealed that CpG island of SOCS-1 was densely methylated in AGS cells. Demethylation treatment by 5'aza-deoxycytidine restored SOCS-1 expression and also suppressed constitutive STAT3 phosphorylation in AGS cells. Moreover, methylation of SOCS-1 was detected in 27.5% (11 of 40) of primary gastric tumours samples, 10% (one of 10) of adjacent noncancer tissues but not in any (zero of nine) normal gastric mucosa. Methylation of SOCS-1 also correlated with the loss of mRNA expression in some primary gastric cancers. In conclusion, this is the first report to demonstrate that hypermethylation of SOCS-1 led to gene silencing in gastric cancer cell line and primary tumour samples. Downregulation of SOCS-1 cooperates with IL-6 in the activation of JAK/STAT pathway in gastric cancer.

Nasopharyngeal carcinoma in situ (NPCIS)--pathologic and clinical perspectives

BACKGROUND

Dysplasia or carcinoma in situ lesions (NPCIS) of the nasopharynx have rarely been reported. The prevalence, biologic behavior, and the transformation period of the pure preinvasive lesions have not been fully explained.

METHODS

All cases of NPCIS were retrospectively reviewed during the period between 1990 and 2000. The clinical features of all cases were studied. The biopsy samples were examined using light microscopy and in situ hybridization (ISH) for EBV-encoded RNA (EBER). The sera taken before and after the transformation were analyzed for anti-viral capsid antigen (VCA) EBV titers and circulating cell-free EBV DNA concentration.

RESULTS

Three cases of NPCIS were identified. Two of the three cases subsequently developed into invasive NPC after initial presentation. The interval of transformation varied from 40 to 48 months. In all three cases, the specimens showed abnormal findings on light microscopy and positive staining for EBER. Elevated anti-VCA titers were present in two of the preinvasive lesions. No cell-free EBV DNA was detected in the sera of these patients during the preinvasive phase of the disease.

CONCLUSIONS

Preinvasive NPC is a rare but distinct entity. Its transformation period can be as long as 4 to 5 years. Elevated anti-VCA titers, in the presence of abnormal cells on light microscopy, should alert the pathologist to perform ISH EBER studies to diagnose this rare condition.