Comparison of molecular profiles derived from untreated and treated SP and non-SP populations showed that the majority of the common CSC signature (932/1,259 genes, 74%) overlapped with the SP fraction-dependent gene set and thus was defined by CSC properties but not ZEB exposure. We confirmed this conclusion through a further comparison of the CSC signature with a ZEB methylation signature that was generated for Huh7, WRL68, and KMCH cells using Illumina Infinium HumanMethylation27 microarray involving 27,578 CpG sites. Only 28 genes overlapped between the 617-gene CSC signature and ZEB methylation signature (990 genes), indicating that the described CSC signature was reflective of intrinsic

selleck screening library CSC properties. Finally, screening the promoters of 118 genes, which best classified HCC patients according to clinical outcome (Fig. 6B) for the presence of 5′-CpG islands using the EMBOSS CpGplot/report (guanine-cytosine content, >50%; ratio of CpG-to-GpC, >0.6; minimum length, 200 bp)27 revealed that Cisplatin price only 52.5% of genes contained promoter CpG islands compared with a 60% expected average within the human genome.28

To test the clinical significance of the SP-ZEB signature, we integrated individual SP signatures with our published gene expression dataset from 139 human HCCs.24 Kaplan-Meier analysis showed that each SP signature independently classified HCC patients according to survival (Supporting Phospholipase D1 Fig. 4D). All three SP signatures were enriched in the

poorly differentiated HCC subtype A, including tumors defined by hepatic stem cell–like traits and worse clinical outcome (HB [hepatoblast] subtype) (Supporting Fig. 4C).24, 29 These findings were confirmed by integrative analysis of the common SP-ZEB signature using gene expression data from 53 HCC patients generated on Illumina beadchips (Fig. 6A,C). To narrow down the common SP-ZEB signature to genes most significantly associated with the identified clusters, we generated a 118-gene classifier using leave-one-out cross-validation and confirmed its predictive value by seven different prediction models (Fig. 6B). The 118-gene set successfully differentiated HCC patients according to overall survival (P < 0.006) and disease recurrence (P < 0.02) (Fig. 6D,E). Notably, removal of genes involved in proliferation and cell cycle did not impact the ability of the signature to classify liver cancer patients according to clinical outcome (P = 0.01).30, 31 Furthermore, a meta-analysis performed on gene expression data from 40 different primary tumor types demonstrated that the 118-gene classifier also predicted survival of patients with other tumors (e.g., lung, breast, kidney) and successfully classified lung adenocarcinoma according to clinical outcome (Fig. 6F, Supporting Fig. 6A,B), suggesting prognostic use of the SP-ZEB signature for cancers other than HCC.21, 32 (A complete list of these genes is provided in Supporting Table 5.