title: Human translocation liposarcoma-CCAAT/enhancer binding protein (C/EBP) homologous protein (TLS-CHOP) oncoprotein prevents adipocyte differentiation by directly interfering with C/EBPbeta function.
abstract: Human translocation liposarcoma (TLS)-CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP) is a fusion oncoprotein found specifically in a malignant tumor of adipose tissue and results from a t(12;16) translocation that fuses the amino-terminal part of TLS to the entire coding region of CHOP. Being that CHOP is a member of the C/EBP transcription factor family, proteins that comprise part of the adipocyte differentiation machinery, we examined whether TLS-CHOP blocked adipocyte differentiation by directly interfering with C/EBP function. Using a single-step retroviral infection protocol, either wild-type or mutant TLS-CHOP were co-expressed along with C/EBPbeta in naïve NIH3T3 cells, and their ability to inhibit C/EBPbeta-driven adipogenesis was determined. TLS-CHOP was extremely effective at blocking adipocyte differentiation when expressed at a level comparable to that observed in human myxoid liposarcoma. This effect of TLS-CHOP required a functional leucine zipper domain and correlated with its ability to heterodimerize with C/EBPbeta and inhibit C/EBPbeta DNA binding and transactivation activity in situ. In contrast, the TLS-CHOP basic region was dispensable, making it unlikely that the inhibitory effect of TLS-CHOP is attributable to unscheduled gene expression resulting from TLS-CHOP's putative transactivation activity. Another adipogenic transcription factor, PPARgamma2, was able to rescue TLS-CHOP-inhibited cells, indicating that TLS-CHOP interferes primarily with C/EBPbeta-driven adipogenesis and not with other requisite events of the adipocyte differentiation program. Together, the results demonstrate that TLS-CHOP blocks adipocyte differentiation by directly preventing C/EBPbeta from binding to and transactivating its target genes. Moreover, they provide strong support for the thesis that a blockade to normal differentiation is an important aspect of the cancer process.
authors.affiliation: Departments of Molecular Biology and Radiation Oncology, Henry Ford Health System, Detroit, Michigan 48202-3450, USA.
authors.forename: G
authors.initials: G
authors.lastname: Adelmant
authors.forename: J D
authors.initials: JD
authors.lastname: Gilbert
authors.forename: S O
authors.initials: SO
authors.lastname: Freytag
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology* / Q000187:drug effects; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D051379:Mice; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology*; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000494:pharmacology*; D010641:Phenotype; D034702:RNA-Binding Protein FUS; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis; D051742:Transcription Factor CHOP; D014157:Transcription Factors / Q000096:biosynthesis / Q000502:physiology*
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D015514:Oncogene Proteins, Fusion; D034702:RNA-Binding Protein FUS; D018160:Receptors, Cytoplasmic and Nuclear; C106030:TLS-CHOP fusion protein, human; D014157:Transcription Factors; D051742:Transcription Factor CHOP; D004247:DNA