Serrated pathway in colorectal carcinogenesis

Serrated adenocarcinoma is a recently described subset of colorectal cancer(CRC),which account for about10%of all CRCs and follows an alternative pathway in which serrated polyps replace the traditional adenoma as the precursor lesion to CRC.Serrated polyps form a heterogeneous group of colorectal lesions that includes hyperplastic polyps(HPs),sessile serrated adenoma(SSA),traditional serrated adenoma(TSA)and mixed polyps.HPs are the most common serrated polyp followed by SSA and TSA.This distinct histogenesis is believed to have a major influence in prevention strategies,patient prognosis and therapeutic impact.Genetically,serrated polyps exhibited also a distinct pattern,with KRAS and BRAF having an important contribution to its development.Two other molecular changes that have been implicated in the serrated pathway include microsatellite instability and the CpG island methylator phenotype.In the present review we will address the current knowledge of serrated polyps,clinical pathological features and will update the most recent findings of its molecular pathways.The understanding of their biology and malignancy potential is imperative to implement a surveillance approach in order to prevent colorectal cancer development.

MicroRNA-31 expression in colorectal serrated pathway progression

MicroRNAs have been increasingly recognized as useful biomarkers for colorectal cancers(CRC).We have recently observed that microRNA-31(miR-31)expression is associated with BRAF mutation and prognosis in CRC.Moreover,high miR-31 expression is frequently detected in sessile serrated adenomas compared with hyperplastic polyps(HPs).These results suggest that miR-31 may contribute to the progression of serrated lesions.At a follow-up colonoscopy,we observed the case of a 75-year-old man with a 7-mm flat-elevated lesion in the cecum and diagnosed the lesion as an early invasive carcinoma with serrated features.Tissue specimens were obtained from the representative areas to compare the molecular alterations in the carcinoma component with those in the HP component.Higher miR-31 expression was observed in the carcinoma component(57-fold increase)and the HP component(8-fold increase)compared with the paired normal mucosa,suggesting that miR-31 may be one of the key molecules in serrated pathway progression.

What could microRNA expression tell us more about colorectal serrated pathway carcinogenesis?

In the last two decades,the vision of a unique carcinogenesis model for colorectal carcinoma(CRC)has completely changed.In addition to the adenoma to carcinoma transition,colorectal carcinogenesis can also occur via the serrated pathway.Small non-coding RNA,known as microRNAs(miRNAs),were also shown to be involved in progression towards malignancy.Furthermore,increased expression of certain miRNAs in premalignant sessile serrated lesions(SSLs)was found,emphasizing their role in the serrated pathway progression towards colon cancer.Since miRNAs function as post-transcriptional gene regulators,they have enormous potential to be used as useful biomarkers for CRC and screening in patients with SSLs particularly.In this review,we have summarized the most relevant information about the specific role of miRNAs and their relevant signaling pathways among different serrated lesions and polyps as well as in serrated adenocarcinoma.Additional focus is put on the correlation between gut immunity and miRNA expression in the serrated pathway,which remains unstudied.

5’tiRNA-Pro-TGG,a novel tRNA halve,promotes oncogenesis in sessile serrated lesions and serrated pathway of colorectal cancer

BACKGROUND Transfer RNA(tRNA)-derived small RNAs(tsRNAs)are small fragments that form when tRNAs severe.tRNA halves(tiRNAs),a subcategory of tsRNA,are involved in the oncogenic processes of many tumors.However,their specific role in sessile serrated lesions(SSLs),a precancerous lesion often observed in the colon,has not yet been elucidated.AIM To identify SSL-related tiRNAs and their potential role in the development of SSLs and serrated pathway of colorectal cancer(CRC).METHODS Small-RNA sequencing was conducted in paired SSLs and their adjacent normal control(NC)tissues.The expression levels of five SSL-related tiRNAs were validated by q-polymerase chain reaction.Cell counting kit-8 and wound healing assays were performed to detect cell proliferation and migration.The target genes and sites of tiRNA-1:33-Pro-TGG-1(5′tiRNA-Pro-TGG)were predicted by TargetScan and miRanda algorithms.Metabolism-associated and immune-related pathways were analyzed by single-sample gene set enrichment analysis.Functional analyses were performed to establish the roles of 5′tiRNA-Pro-TGG based on the target genes.RESULTS In total,we found 52 upregulated tsRNAs and 28 downregulated tsRNAs in SSLs compared to NC.The expression levels of tiRNA-1:33-Gly-CCC-2,tiRNA-1:33-Pro-TGG-1,and tiRNA-1:34-Thr-TGT-4-M25′tiRNAs were higher in SSLs than those in NC,while that of 5′tiRNA-Pro-TGG was associated with the size of SSLs.It was demonstrated that 5′tiRNAPro-TGG promoted cell proliferation and migration of RKO cell in vitro.Then,heparanase 2(HPSE2)was identified as a potential target gene of 5′tiRNA-Pro-TGG.Its lower expression was associated with a worse prognosis in CRC.Further,lower expression of HPSE2 was observed in SSLs compared to normal controls or conventional adenomas and in BRAF-mutant CRC compared to BRAF-wild CRC.Bioinformatics analyses revealed that its low expression was associated with a low interferonγresponse and also with many metabolic pathways such as riboflavin,retinol,and cytochrome p450 drug metabolism pathways.CONCLUSION tiRNAs may profoundly impact the development of SSLs.5′tiRNA-Pro-TGG potentially promotes the progression of serrated pathway CRC through metabolic and immune pathways by interacting with HPSE2 and regulating its expression in SSLs and BRAF-mutant CRC.In the future,it may be possible to use tiRNAs as novel biomarkers for early diagnosis of SSLs and as potential therapeutic targets in serrated pathway of CRC.

Serrated polyposis syndrome:Molecular,pathological and clinical aspects

Hyperplastic polyps have traditionally been considered not to have malignant potential.New pathological classification of serrated polyps and recent discoveries about the serrated pathway of carcinogenesis have revolutionized the concepts and revitalized the research in this area.Until recently,it has been thought that most colorectal cancers arise from conventional adenomas via the traditional tumor suppressor pathway initiated by a mutation of the APC gene,but it has been found thatthis pathway accounts for only approximately 70%-80% of colorectal cancer(CRC)cases.The majority of the remaining colorectal cancer cases follow an alternative pathway leading to CpG island methylator phenotype carcinoma with BRAF mutation and with or without microsatellite instability.The mechanism of carcinomas arising from this alternative pathway seems to begin with an activating mutation of the BRAF oncogene.Serrated polyposis syndrome is a relatively rare condition characterized by multiple and/or large serrated polyps of the colon.Clinical characteristics,etiology and relationship of serrated polyposis syndrome to CRC have not been clarified yet.Patients with this syndrome show a high risk of CRC and both sporadic and hereditary cases have been described.Clinical criteria have been used for diagnosis and frequent colonoscopy surveillance should be performed in order to prevent colorectal cancer.In this review,we try to gather new insights into the molecular pathogenesis of serrated polyps in order to understand their possible clinical implications and to make an approach to the management of this syndrome.

From traditional serrated adenoma to tubulovillous adenoma and beyond

It is well established that colorectal cancer develops from a series of precursor epithelial polyps, including tubular adenomas, villous/tubulovillous adenomas (VA/TVA), sessile serrated adenomas (SSA) and traditional serrated adenomas (TSA). Of these, TSAs are least common and account for only 5% of all serrated polyps. TSAs are characterised by the presence of a “pinecone-like” architecture, granular eosinophilic cytoplasm, luminal serrations, ectopic crypt foci (ECF) and elongated, pencillate nuclei. However, the distinct slit-like luminal serrations, reminiscent of small bowel mucosa, appear to be the most unique and reproducible feature to distinguish TSAs from other polyps. There is a contention that TSAs are not inherently dysplastic and that the majority do not show cytological atypia. Two types of dysplasia are associated with TSA. Serrated dysplasia is less well recognised and less commonly encountered than adenomatous dysplasia. In addition, it is now becoming increasingly evident that TSAs can be admixed with HP, SSA and VA/TVA. At a genetic level, polyps may switch phenotype as they accumulate genetic changes, evolving from a serrated pathway to a more conventional one, which could be the basis for a spectrum theory starting out with a TSA with serration and ECF evolving into a TSA with conventional dysplasia and, eventually, to a well-developed conventional adenoma. Nevertheless, there is an exigency for future studies to provide further illumination and bridge the gaps in our present understanding.

IGF2 differentially methylated region hypomethylation in relation to pathological and molecular features of serrated lesions

AIM: To investigate insulin-like growth factor 2 (IGF2) differentially methylated region (DMR)0 hypomethylation in relation to clinicopathological and molecular features in colorectal serrated lesions.

Missed colorectal cancers in a fecal immunochemical test-based screening program: Molecular profiling of interval carcinomas

BACKGROUND For optimizing fecal immunochemical test(FIT)-based screening programs,reducing the rate of missed colorectal cancers(CRCs)by FIT(FIT-interval CRCs)is an important aspect.Knowledge of the molecular make-up of these missed lesions could facilitate more accurate detection of all(precursor)lesions.AIM To compare the molecular make-up of FIT-interval CRCs to lesions that are detected by FIT[screen-detected CRCs(SD-CRCs)].METHODS FIT-interval CRCs observed in a Dutch pilot-program of FIT-based screening were compared to a control group of SD-CRCs in a 1:2 ratio,resulting in 27 FIT-interval CRC and 54 SD-CRCs.Molecular analyses included microsatellite instability(MSI),CpG island methylator phenotype(CIMP),DNA sequence mutations and copy number alterations(CNAs).RESULTS Although no significant differences were reached,FIT-interval CRCs were more often CIMP positive and MSI positive(33%CIMP in FIT-interval CRCs vs 21%in SD-CRCs(P=0.274);19%MSI in FIT-interval CRCs vs 12%in SD-CRCs(P=0.469)),and showed more often serrated pathway associated features such as BRAF(30%vs 12%,P=0.090)and PTEN(15%vs 2.4%,P=0.063)mutations.APC mutations,a classic feature of the adenoma-carcinoma-sequence,were more abundant in SD-CRCs(68%vs 40%in FIT-interval CRCs P=0.035).Regarding CNAs differences between the two groups;FIT-interval CRCs less often showed gains at the regions 8p11.22-q24.3(P=0.009),and more often gains at 20p13-p12.1(P=0.039).CONCLUSION Serrated pathway associated molecular features seem to be more common in FIT-interval CRCs,while classic adenoma carcinoma pathway associated molecular features seem to be more common in SD-CRCs.This indicates that proximal serrated lesions may be overrepresented among FITinterval CRCs.