ABSTRACT
The human oncogene JUN encodes a component of the AP-1 complex and is consequently involved in a wide range of pivotal cellular processes, including cell proliferation, transformation, and apoptosis. Nevertheless, despite extensive analyses of its functions, it has never been directly involved in a human cancer. We demonstrate here that it is highly amplified and overexpressed in undifferentiated and aggressive human sarcomas, which are blocked at an early step of adipocyte differentiation. We confirm by cellular and xenograft mouse models recapitulating these sarcoma genetics that the failure to differentiate is dependent upon JUN amplification/overexpression.
Subject(s)
Adipocytes/pathology , Cell Differentiation , Gene Amplification , Liposarcoma/pathology , Proto-Oncogene Proteins c-jun/genetics , 3T3-L1 Cells , Adipocytes/metabolism , Adipogenesis , Aged , Animals , Chromosomes, Artificial, Bacterial , Chromosomes, Human, Pair 1/genetics , Female , Gene Expression Profiling , Gene Expression Regulation , Humans , Liposarcoma/genetics , Liposarcoma/metabolism , Mice , Mice, Nude , Proto-Oncogene Proteins c-jun/metabolism , RNA, Messenger/genetics , RNA, Messenger/metabolism , Retroperitoneal Neoplasms/genetics , Retroperitoneal Neoplasms/metabolism , Retroperitoneal Neoplasms/pathology , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Protein kinases orthologous with Cak1 of Saccharomyces cerevisiae (ScCak1) appear specific to ascomycetes. ScCak1 phosphorylates Cdc28, the cyclin-dependent kinase (CDK) governing the cell cycle, as well as Kin28, Bur1 and Ctk1, CDKs required for the transcription process performed by RNA polymerase II (RNA Pol II). Using genetic methods, we found that Cak1 genetically interacts with Paf1 and Ctr9, two components belonging to the PAF1 elongation complex needed for histone modifications, and with Ssu72, a protein phosphatase that dephosphorylates serine-5 phosphate in the RNA Pol II C-terminal domain. We present evidence suggesting that the interactions linking Cak1 with the PAF1 complex and with Ssu72 are not direct but mediated via Ctk1 and Bur1. We discuss the possibility that Ssu72 intervenes at the capping checkpoint step of the transcription cycle.
Subject(s)
Carrier Proteins/metabolism , Cyclin-Dependent Kinases/metabolism , Nuclear Proteins/metabolism , Protein Kinases/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/enzymology , Base Sequence , Carrier Proteins/genetics , Cell Cycle Proteins/genetics , Cell Cycle Proteins/metabolism , Cyclin-Dependent Kinases/genetics , DNA, Complementary/genetics , DNA, Fungal/genetics , Genes, Fungal , Genes, Lethal , Mutation , Nuclear Proteins/genetics , Phosphoprotein Phosphatases , Plasmids/genetics , Protein Kinases/genetics , Saccharomyces cerevisiae/genetics , Saccharomyces cerevisiae/metabolism , Saccharomyces cerevisiae Proteins/genetics , Suppression, Genetic , Temperature , Transcriptional Elongation Factors , mRNA Cleavage and Polyadenylation Factors , Cyclin-Dependent Kinase-Activating KinaseABSTRACT
Ssu72 is an essential yeast protein that is involved in transcription. It physically interacts with transcription initiation and termination complexes. In this report, we provide evidence that Ssu72 is a phosphatase that physically interacts with the CTD kinase Kin28 and functionally interacts with the CTD phosphatase Fcp1. A genome-wide expression analysis of mutant ssu72-ts69 during growth in complete medium revealed a number of defects, including the accumulation of a limited number of mRNAs and the read-through transcription of small nucleolar RNAs and of some mRNAs. We hypothesize that Ssu72 plays a key role in the transcription termination of certain transcripts, possibly by promoting RNA polymerase pausing and release. The possibility that the CTD of the largest subunit of RNA polymerase II is a substrate of Ssu72 is discussed.