Polycomb group (PcG) proteins function to maintain the stable epigenetic repression of homeotic genes and other important developmental and cell cycle regulatory genes. Such maintenance establishes a form of cellular memory for its identity or state of differentiation. Accumulating evidence indicates that perturbation of this transcriptional memory may be required for tumor progression and may represent a hallmark of cancer. We have identified a novel gene encoding a human homologue of the Drosophila polycomblike protein, hPCL3. Through alternative polyadenylation and/or splicing, the gene encodes two nuclear proteins, hPCL3S and hPCL3L. Both proteins repressed transcription upon recruitment to the proximity of an HSV-tk promoter by a Gal4 DNA binding domain. Interestingly, the products of the hPCL3 gene, particularly the short form, hPCL3S, are markedly overexpressed in many types of cancers, including colon, skin, lung, rectal, cervical, uterus, and liver cancers. This increase in expression correlated with tumor progression. Both hPCL3S and hPCL3L messages were increased dramatically in most cell lines derived from various stages of melanoma and glioma tumor progression. Thus, our data link PcG deregulation to the progression of multiple cancers and may have important implications for unraveling the mechanisms of tumor progression.
PcG (Polycomb group) proteins are conserved transcriptional repressors essential to regulate cell fate and to maintain epigenetic cellular memory. They work in concert through two main families of chromatin-modifying complexes, PRC1 (Polycomb repressive complex 1) and PRC2-4. In Drosophila, PRC2 contains the H3K27 histone methyltransferase E(Z) whose trimethylation activity towards PcG target genes is stimulated by PCL (Polycomb-like). In the present study, we have examined hPCL3, one of its three human paralogues. Through alternative splicing, hPCL3 encodes a long isoform, hPCL3L, containing an N-terminal TUDOR domain and two PHDs (plant homeodomains) and a smaller isoform, hPCL3S, lacking the second PHD finger (PHD2). By quantitative reverse transcription-PCR analyses, we showed that both isoforms are widely co-expressed at high levels in medulloblastoma. By co-immunoprecipitation analyses, we demonstrated that both isoforms interact with EZH2 through their common TUDOR domain. However, the hPCL3L-specific PHD2 domain, which is better conserved than PHD1 in the PCL family, is also involved in this interaction and implicated in the self-association of hPCL3L. Finally, we have demonstrated that both hPCL3 isoforms are physically associated with EZH2, but in different complexes. Our results provide the first evidence that the two hPCL3 isoforms belong to different complexes and raise important questions about their relative functions, particularly in tumorigenesis.
PcG (Polycomb group) proteins are conserved transcriptional repressors essential to regulate cell fate and to maintain epigenetic cellular memory. They work in concert through two main families of chromatin-modifying complexes, PRC1 (Polycomb repressive complex 1) and PRC2-4. In Drosophila, PRC2 contains the H3K27 histone methyltransferase E(Z) whose trimethylation activity towards PcG target genes is stimulated by PCL (Polycomb-like). In the present study, we have examined hPCL3, one of its three human paralogues. Through alternative splicing, hPCL3 encodes a long isoform, hPCL3L, containing an N-terminal TUDOR domain and two PHDs (plant homeodomains) and a smaller isoform, hPCL3S, lacking the second PHD finger (PHD2). By quantitative reverse transcription-PCR analyses, we showed that both isoforms are widely co-expressed at high levels in medulloblastoma. By co-immunoprecipitation analyses, we demonstrated that both isoforms interact with EZH2 through their common TUDOR domain. However, the hPCL3L-specific PHD2 domain, which is better conserved than PHD1 in the PCL family, is also involved in this interaction and implicated in the self-association of hPCL3L. Finally, we have demonstrated that both hPCL3 isoforms are physically associated with EZH2, but in different complexes. Our results provide the first evidence that the two hPCL3 isoforms belong to different complexes and raise important questions about their relative functions, particularly in tumorigenesis.
Polycomb group (PcG) proteins function to maintain the stable epigenetic repression of homeotic genes and other important developmental and cell cycle regulatory genes. Such maintenance establishes a form of cellular memory for its identity or state of differentiation. Accumulating evidence indicates that perturbation of this transcriptional memory may be required for tumor progression and may represent a hallmark of cancer. We have identified a novel gene encoding a human homologue of the Drosophila polycomblike protein, hPCL3. Through alternative polyadenylation and/or splicing, the gene encodes two nuclear proteins, hPCL3S and hPCL3L. Both proteins repressed transcription upon recruitment to the proximity of an HSV-tk promoter by a Gal4 DNA binding domain. Interestingly, the products of the hPCL3 gene, particularly the short form, hPCL3S, are markedly overexpressed in many types of cancers, including colon, skin, lung, rectal, cervical, uterus, and liver cancers. This increase in expression correlated with tumor progression. Both hPCL3S and hPCL3L messages were increased dramatically in most cell lines derived from various stages of melanoma and glioma tumor progression. Thus, our data link PcG deregulation to the progression of multiple cancers and may have important implications for unraveling the mechanisms of tumor progression.
Protein involved in the transfer of genetic information from DNA to messenger RNA (mRNA) by DNA-directed RNA polymerase. In the case of some RNA viruses, protein involved in the transfer of genetic information from RNA to messenger RNA (mRNA) by RNA-directed RNA polymerase.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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