We performed a genomic, transcriptomic, and immunophenotypic study of 347 patients with diffuse large B-cell lymphoma (DLBCL) to uncover the molecular basis underlying acquired defi ciency of MHC expression. Low MHC-II expression defi nes tumors originating from the centroblast-rich dark zone of the germinal center (GC) that was associated with inferior prognosis. MHC-II-defi cient tumors were characterized by somatically acquired gene mutations reducing MHC-II expression and a lower amount of tumor-infi ltrating lymphocytes. In particular, we demonstrated a strong enrichment of EZH2 mutations in both MHC-I-and MHC-II-negative primary lymphomas, and observed reduced MHC expression and T-cell infi ltrates in murine lymphoma models expressing mutant Ezh2 Y641. Of clinical relevance, EZH2 inhibitors signifi cantly restored MHC expression in EZH2-mutated human DLBCL cell lines. Hence, our fi ndings suggest a tumor progression model of acquired immune escape in GC-derived lymphomas and pave the way for development of complementary therapeutic approaches combining immunotherapy with epigenetic reprogramming. SIGNIFICANCE: We demonstrate how MHC-defi cient lymphoid tumors evolve in a cell-of-origin-specifi c context. Specifi cally, EZH2 mutations were identifi ed as a genetic mechanism underlying acquired MHC defi ciency. The paradigmatic restoration of MHC expression by EZH2 inhibitors provides the rationale for synergistic therapies combining immunotherapies with epigenetic reprogramming to enhance tumor recognition and elimination.
Sporadic clear cell renal cell carcinoma (cRCC) is genetically characterized by the recurrent loss of the short arm of chromosome 3, with a hotspot for copy number loss in the 3p21 region. We applied a method called "gene identification by nonsense-mediated mRNA decay inhibition" to a panel of 10 cRCC cell lines with 3p21 copy number loss to identify biallelic inactivated genes located at 3p21. This revealed inactivation of the histone methyltransferase gene SETD2, located on 3p21.31, as a common event in cRCC cells. SETD2 is nonredundantly responsible for trimethylation of the histone mark H3K36. Consistent with this function, we observed loss or a decrease of H3K36me3 in 7 out of the 10 cRCC cell lines. Identification of missense mutations in 2 out of 10 primary cRCC tumor samples added support to the involvement of loss of SETD2 function in the development of cRCC tumors. Cancer Res; 70(11); 4287-91. ©2010 AACR.
In the past decade important progress has been made in our understanding of the epigenetic regulatory machinery. It has become clear that genetic aberrations in multiple epigenetic modifier proteins are associated with various types of cancer. Moreover, targeting the epigenome has emerged as a novel tool to treat cancer patients. Recently, the first drugs have been reported that specifically target SETD2-negative tumors. In this review we discuss the studies on the associated protein, Set domain containing 2 (SETD2), a histone modifier for which mutations have only recently been associated with cancer development. Our review starts with the structural characteristics of SETD2 and extends to its corresponding function by combining studies on SETD2 function in yeast, Drosophila, Caenorhabditis elegans, mice, and humans. SETD2 is now generally known as the single human gene responsible for trimethylation of lysine 36 of Histone H3 (H3K36). H3K36me3 readers that recruit protein complexes to carry out specific processes, including transcription elongation, RNA processing, and DNA repair, determine the impact of this histone modification. Finally, we describe the prevalence of SETD2-inactivating mutations in cancer, with the highest frequency in clear cell Renal Cell Cancer, and explore how SETD2-inactivation might contribute to tumor development.
The study of human microRNAs is seriously hampered by the lack of proper tools allowing genome-wide identification of miRNA targets. We performed Ribonucleoprotein ImmunoPrecipitation—gene Chip (RIP-Chip) using antibodies against wild-type human Ago2 in untreated Hodgkin lymphoma (HL) cell lines. Ten to thirty percent of the gene transcripts from the genome were enriched in the Ago2-IP fraction of untreated cells, representing the HL miRNA-targetome. In silico analysis indicated that ∼40% of these gene transcripts represent targets of the abundantly co-expressed miRNAs. To identify targets of miR-17/20/93/106, RIP-Chip with anti-miR-17/20/93/106 treated cells was performed and 1189 gene transcripts were identified. These genes were analyzed for miR-17/20/93/106 target sites in the 5′-UTRs, coding regions and 3′-UTRs. Fifty-one percent of them had miR-17/20/93/106 target sites in the 3′-UTR while 19% of them were predicted miR-17/20/93/106 targets by TargetScan. Luciferase reporter assay confirmed targeting of miR-17/20/93/106 to the 3′-UTRs of 8 out of 10 genes. In conclusion, we report a method which can establish the miRNA-targetome in untreated human cells and identify miRNA specific targets in a high throughput manner. This approach is applicable to identify miRNA targets in any human tissue sample or purified cell population in an unbiased and physiologically relevant manner.
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