We recently reported a role of Polycomb repressive complex 2 (PRC2) and PRC2 trimethylation of histone 3 lysine 27 (H3K27me3) in the regulation of homeobox (HOX) (Marcinkiewicz and Gudas, 2013) gene transcript levels in human oral keratinocytes (OKF6-TERT1R) and tongue squamous cell carcinoma (SCC) cells. SIX2 the H3K9me3 levels were conversely higher in SCC-9 than in OKF6-TERT1R. The H3K79me3 mark was detectable only at IRX1 in OKF6-TERT1R and at IRX4 in SCC-9 cells. The levels of H3K4me3 and H3K36me3 marks correlate with the transcript levels of the assessed homeobox genes in both OKF6-TERT1R and SCC-9. We detected generally lower CpG methylation levels on DNA in SCC-9 cells at annotated genomic regions which were differentially methylated between OKF6-TERT1R and SCC-9 cells; however, some genomic regions, including the HOX gene clusters, showed DNA methylation at higher levels in SCC-9 than OKF6-TERT1R. Thus, both altered histone modification patterns and changes in DNA methylation are associated with dysregulation of homeobox gene expression in human oral cavity SCC cells, and this dysregulation potentially plays a role in the neoplastic phenotype Cd8a of oral keratinocytes. valuevaluevaluevaluevaluevaluevaluevaluewhich were differentially methylated between OKF6-TERT1R and SCC-9 cells. Open in a separate window Figure 4 DNA methylation levels along annotated gene bodies and proximal promoter regions with at least a 20% point difference in methylation levels between OKF6-TERT1R and SCC-9 cellsMethylation levels expressed as % (see: Methods section) along Teglicar annotated gene bodies (top panel) or proximal promoter regions ((defined as a 2000 bp sequence immediately upstream of the first TSS; bottom panel) with at least a 20 percent point difference in methylation levels between the OKF6-TERT1R and SCC-9 cells are shown in OKF6-TERT1R (x-axis) versus SCC-9 cells (y-axis). This shows the lower methylation levels along gene bodies and gene proximal promoter regions in SCC-9 as compared to OKF6-TERT1R cells. Some promoters frequently methylated in human OSCC samples have higher methylation levels in SCC-9 than in OKF6-TERT1R Next, we reviewed the literature to identify genes known to undergo promoter methylation during carcinogenesis, and we compiled gene body and proximal promoter region ERRBS data for these genes (Table 2). Many of the Teglicar genes with promoter regions frequently methylated in human OSCC samples versus normal oral mucosa also show higher methylation levels in their proximal promoter regions in SCC-9 compared to OKF6-TERT1R cells; CDKN2A, 76.7% vs. 56.4%; DAPK1, 10.8% vs. 4.4%; IRF8, 38.2% vs. 19.7%; IRX1, 66.1% vs. 2.7%; MGMT1, 28.1% vs. 23.1%; p53, 96.0% vs. 86.0%; p73, 11.0% vs. 6.5%; and RAR, 20.0% vs. 11.1% (Table 2). Other genes have higher methylation levels along gene bodies in SCC-9 than in OKF6-TERT1R cells; CDKN2A, 69.6% vs. 32.8%; EBF3, 61.7% vs. 28.1%; HOXA9, 70.5% vs. 12.1%; IRX1, 72.9% vs. 45.9%; and SERPINB5, 83.9% vs. 61.2% (Table 2). In contrast, some genes show higher methylation levels along gene bodies in OKF6-TERT1R compared to SCC-9 cells: AIM2, 40.3% vs. 7.7%; DCC, 31.6% vs. 2.9%; and MGMT, 39.4% vs. 6.2% (Table 2). These data suggest that some of the differences in transcript levels between OKF6-TERT1R and SCC-9 may result from different DNA methylation patterns. Table 2 Methylation levels along gene body and proximal promoter regions for genes frequently methylated in oral squamous cell carcinoma. is shown (Table 3). Interestingly, HOX genes show higher DNA methylation levels in SCC-9 than in OKF6-TERT1R. HOXB3, HOXB7, HOXD4, HOXC4, and HOXD10 have higher DNA methylation levels along their gene bodies in SCC-9 than in OKF6-TERT1R (HOXB3, 69.2% vs. 5.2%; HOXB7, 20.6% vs. 2.5%; HOXD4, 54.5% vs. 11.3%; HOXC4, 46.2% vs. 9.0%; and HOXD10, 59.9% vs. 11.8%; Table 3). These data are consistent with reports in the books that more positively transcribed genes have DNA methylation in their gene bodies (Hahn et al., 2011; Hellman and Chess, 2007; Jjingo et al., 2012; Kulis et al., 2013; Maunakea et al., 2010; Nguyen et al., 2001; Shenker and Teglicar Flanagan, 2012). Additionally, HOX genes B3, B7, D4, and C4 have higher methylation levels along their proximal promoter regions in SCC-9 than in OKF6-TERT1R (HOXB3, 78.4% vs. 13.4%; HOXB7, 77.0% vs. 9.1%; HOXD4, 72.6% vs. 22.7%; HOXC4 50.2% vs. 9.4%; Table 3). The DNA methylation levels at individual CpGs within the genomic regions of entire HOX gene clusters are also shown (Fig. 5(c)). Table 3 Gene body and promoter methylation data.