Distinct oncogenic signatures in malignant PEComa and leiomyosarcoma identified by integrative RNA-seq and H3K27ac ChIP-seq analysis.

Abstract

11552 Background: Malignant perivascular epithelioid cell tumor (PEComa) and leiomyosarcoma (LMS) are two sarcomas with overlapping morphologic and immunophenotypic features which can make their diagnostic distinction challenging. We aimed to characterize the transcriptional and epigenetic landscape of PEComa and LMS to identify distinguishing features. Methods: We performed whole transcriptome RNA-sequencing on 19 PEComas and compared their gene expression profile to 259 sarcomas from The Cancer Genome Atlas (TCGA) including 104 LMS. ChIP-sequencing for H3K27ac, a histone modification associated with activation of nearby genes/open chromatin, was conducted on 9 malignant PEComas and 12 LMS and were compared with publicly available data from 4 other sarcoma subtypes (chordoma; osteosarcoma; undifferentiated pleomorphic sarcoma; rhabdomyosarcoma; n = 29 tumors). Results: Genome-wide epigenetic and transcriptional analyses revealed overlapping patterns between PEComa and LMS, which were distinct from other sarcomas. However, we also identified a set of highly expressed and epigenetically distinct transcripts which may represent diagnostic?biomarkers: e.g., DAPL1, MLANA, SULT1C2, GPR143, and CHI3L1 for PEComa; and MYOCD, WDFC2, DES, MYH11, and CNN1 for LMS; each of which showed >17x fold higher expression for each tumor entity by DESeq2 (FDR<0.0001). Gene Set Enrichment Analyses (GSEA) demonstrated enrichment in the KEGG Lysosome pathway for PEComa (FDR=0.11), whereas myogenesis and smooth muscle contraction pathways were enriched in LMS (FDR=0.09). Integrative transcriptomic and epigenetic analyses revealed a unique set of master core transcription factors for each tumor type including among others MYOCD for LMS; MITF for PEComa, which require further functional investigation. Twelve selected genes including new as well as known and standard diagnostic markers (e.g., DAPL1, MLANA, GPR143, PNL2, CHI3L1, DES, MYH11, ER, CD68, PU.1, pS6 and CNN1) were validated by immunohistochemistry (IHC) in multiple sections from PEComa and LMS (n = 26). The combination of three melanocytic markers (HMB45, MLANA, PNL2) and pS6 can distinguish LMS from PEComas (**** p<0.0001). IHC for CD68 and PU.1 macrophage markers did not show any difference regarding the degree of immune infiltration in PEComa vs. LMS. Conclusions: Our studies revealed novel epigenetic signatures translating into lysosomal and melanocytic proteins for PEComa and myogenic proteins for LMS, which may serve as useful diagnostic biomarkers in the distinction of these two sarcoma subtypes.