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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.METHODS:To accurately analyze the association between the histological types and molecular features of each type of serrated lesion,we consecutively collected1386 formalin-fixed paraffin-embedded tissue specimens that comprised all histological types[hyperplastic polyps(HPs,n=121),sessile serrated adenomas(SSAs,n=132),traditional serrated adenomas(TSAs,n=111),non-serrated adenomas(n=195),and colorectal cancers(n=827)].We evaluated the methylation levels of IGF2 DMR0 and long interspersed nucleotide element-1(LINE-1)in HPs(n=115),SSAs(n=120),SSAs with cytological dysplasia(n=10),TSAs(n=91),TSAs with high-grade dysplasia(HGD)(n=15),non-serrated adenomas(n=80),non-serrated adenomas with HGD(n=105),and CRCs(n=794).For the accurate quantification of the relative methylation levels(scale 0%-100%)of IGF2 DMR0 and LINE-1,we used bisulfite pyrosequencing method.Tumor specimens were analyzed for microsatellite instability,KRAS(codons 12 and 13),BRAF(V600E),and PIK3CA(exons 9and 20)mutations;MLH1 and MGMT methylation;and IGF2 expression by immunohistochemistry.RESULTS:The distribution of the IGF2 DMR0 methylation level in 351 serrated lesions and 185 non-serrated adenomas(with or without HGD)was as follows:mean61.7,median 62.5,SD 18.0,range 5.0-99.0,interquartile range 49.5-74.4.The IGF2 DMR0 methylation level was divided into quartiles(Q1≥74.5,Q2 62.6-74.4,Q3 49.6-62.5,Q4≤49.5)for further analysis.With regard to the histological type,the IGF2 DMR0 methylation levels of SSAs(mean±SD,73.1±12.3)were significantly higher than those of HPs(61.9±20.5),TSAs(61.6±19.6),and non-serrated adenomas(59.0±15.8)(P<0.0001).The IGF2 DMR0 methylation level was inversely correlated with the IGF2 expression level(r=-0.21,P=0.0051).IGF2 DMR0 hypomethylation was less frequently detected in SSAs compared with HPs,TSAs,and non-serrated adenomas(P<0.0001).Multivariate logistic regression analysis also showed that IGF2 DMR0 hypomethylation was inversely associated with SSAs(P<0.0001).The methylation levels of IGF2 DMR0 and LINE-1 in TSAs with HGD(50.2±18.7and 55.7±5.4,respectively)were significantly lower than those in TSAs(61.6±19.6 and 58.8±4.7,respectively)(IGF2 DMR0,P=0.038;LINE-1,P=0.024).CONCLUSION:IGF2 DMR0 hypomethylation may be an infrequent epigenetic alteration in the SSA pathway.Hypomethylation of IGF2 DMR0 and LINE-1 may play a role in TSA pathway progression.
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. METHODS: To accurately analyze the association between the histological types and molecular features of each type of serrated lesion, we consecutively collected1386 formalin-fixed paraffin-embedded tissue specimens that comprised all histological types [hyperplastic polyps (HPs, n = 121), sessile serrated adenomas (SSAs, n = 132) 111), non-serrated adenomas (n = 195), and colorectal cancers (n = 827)]. We evaluated the methylation levels of IGF2 DMR0 and long interspersed nucleotide element- 1 (LINE- 1) , SSAs (n = 120), SSAs with cytological dysplasia (n = 10), TSAs (n = 91), TSAs with high-grade dysplasia (n = 15), non-serrated adenomas non-serrated adenomas with HGD (n = 105), and CRCs (n = 794). For the accurate quantification of the relative methylation levels (scale 0% -100%) of IGF2 DMRO and LINE-1, we used bisulfite pyrosequencing method. Tumor specimens were analyzed for microsatellite instability, KRAS (codons 12 and 13), BRAF (V600E), and PIK3CA (exons 9 and 20) mutations; MLH1 and MGMT methylation; expression by immunohistochemistry .RESULTS: The distribution of the IGF2 DMR0 methylation level in 351 serrated lesions and 185 non-serrated adenomas (with or without HGD) was as follows: mean61.7, median 62.5, SD 18.0, range 5.0-99.0, interquartile range 49.5-74.4.The IGF2 DMRO methylation level was divided into quartiles (Q1 ≧ 74.5, Q2 62.6-74.4, Q3 49.6-62.5, Q4 ≦ 49.5) for further analysis. Regard regard to the histological type, the IGF2 DMR0 methylation levels of SSAs (mean ± SD, 73.1 ± 12.3) were significantly higher than those of HPs (61.9 ± 20.5), TSAs (61.6 ± 19.6), and non-serrated adenomas (59.0 ± 15.8) level was inversely correlated with the IGF2 expression level (r = -0.21, P = 0.0051) .IGF2 DMR0 hypomethylation was less frequently detected in SSAs comparedwith HPs, TSAs, and non-serrated adenomas (P <0.0001) .Multivariate logistic regression analysis also showed that IGF2 DMR0 hypomethylation was inversely associated with SSAs (P <0.0001). The methylation levels of IGF2 DMR0 and LINE- 1 in TSAs with HCL (50.2 ± 18.7 and 55.7 ± 5.4, respectively) were significantly lower than those in TSAs (61.6 ± 19.6 and 58.8 ± 4.7, respectively) (IGF2 DMR0, P = 0.038; DMR0 hypomethylation may be an infrequent epigenetic alteration in the SSA pathway. Hypomthylation of IGF2 DMR0 and LINE-1 may play a role in TSA pathway progression.