ABSTRACT
MCM3 acetylase (MCM3AP) and germinal-centre associated nuclear protein (GANP) are transcribed from the same locus and are therefore confused in databases because the MCM3 acetylase DNA sequence is contained entirely within the much larger GANP sequence and the entire MCM3AP sequence is identical to the carboxy terminus of GANP. Thus, the MCM3AP and GANP genes are read in the same reading frame and MCM3AP is an N-terminally truncated region of GANP. However, we show here that MCM3AP and GANP are different proteins, occupying different locations in the cell and transcribed from different promoters. Intriguingly, a promoter for MCM3AP lies within an intron of GANP. This report is an interesting example in nature of two separate gene products from the same locus that perform two entirely different functions in the cell. Therefore, to avoid further confusion, they should now be referred to as separate but overlapping genes.
Subject(s)
Acetyltransferases/genetics , Genes, Overlapping , Databases, Genetic , Genetic Loci , Genome, Human , HEK293 Cells , Humans , Intracellular Signaling Peptides and Proteins , Introns , Nuclear Proteins/genetics , Promoter Regions, Genetic , RNA, Messenger/genetics , Sequence Analysis, DNA , Transcription, GeneticABSTRACT
Bulk nuclear export of messenger ribonucleoproteins (mRNPs) through nuclear pore complexes (NPCs) is mediated by NXF1. It binds mRNPs through adaptor proteins such as ALY and SR splicing factors and mediates translocation through the central NPC transport channel via transient interactions with FG nucleoporins. Here, we show that mammalian cells require GANP (germinal center-associated nuclear protein) for efficient mRNP nuclear export and for efficient recruitment of NXF1 to NPCs. Separate regions of GANP show local homology to FG nucleoporins, the yeast mRNA export factor Sac3p, and the mammalian MCM3 acetyltransferase. GANP interacts with both NXF1 and NPCs and partitions between NPCs and the nuclear interior. GANP depletion inhibits mRNA export, with retention of mRNPs and NXF1 in punctate foci within the nucleus. The GANP N-terminal region that contains FG motifs interacts with the NXF1 FG-binding domain. Overexpression of this GANP fragment leads to nuclear accumulation of both poly(A)(+)RNA and NXF1. Treatment with transcription inhibitors redistributes GANP from NPCs into foci throughout the nucleus. These results establish GANP as an integral component of the mammalian mRNA export machinery and suggest a model whereby GANP facilitates the transfer of NXF1-containing mRNPs to NPCs.
Subject(s)
Acetyltransferases/metabolism , Germinal Center/metabolism , Nuclear Proteins/metabolism , RNA, Messenger/metabolism , Acetyltransferases/antagonists & inhibitors , Acetyltransferases/genetics , Active Transport, Cell Nucleus , Amino Acid Sequence , Animals , Base Sequence , Cell Line , Humans , Intracellular Signaling Peptides and Proteins , Mammals , Models, Biological , Molecular Sequence Data , Nuclear Proteins/antagonists & inhibitors , Nuclear Proteins/genetics , Nucleocytoplasmic Transport Proteins/antagonists & inhibitors , Nucleocytoplasmic Transport Proteins/genetics , Nucleocytoplasmic Transport Proteins/metabolism , Phosphoproteins/genetics , RNA, Messenger/genetics , RNA, Small Interfering/genetics , RNA-Binding Proteins/antagonists & inhibitors , RNA-Binding Proteins/genetics , RNA-Binding Proteins/metabolism , Ribonucleoproteins/metabolism , Sequence Homology, Amino AcidABSTRACT
The extracellular matrix (ECM) can induce chemotherapy resistance via AKT-mediated inhibition of apoptosis. Here, we show that loss of the ECM protein TGFBI (transforming growth factor beta induced) is sufficient to induce specific resistance to paclitaxel and mitotic spindle abnormalities in ovarian cancer cells. Paclitaxel-resistant cells treated with recombinant TGFBI protein show integrin-dependent restoration of paclitaxel sensitivity via FAK- and Rho-dependent stabilization of microtubules. Immunohistochemical staining for TGFBI in paclitaxel-treated ovarian cancers from a prospective clinical trial showed that morphological changes of paclitaxel-induced cytotoxicity were restricted to areas of strong expression of TGFBI. These data show that ECM can mediate taxane sensitivity by modulating microtubule stability.
Subject(s)
Extracellular Matrix Proteins/metabolism , Microtubules/drug effects , Microtubules/metabolism , Ovarian Neoplasms/metabolism , Paclitaxel/pharmacology , Transforming Growth Factor beta/metabolism , Antineoplastic Agents, Phytogenic/pharmacology , Cell Adhesion/drug effects , Cell Death/drug effects , Cell Line, Tumor , Centrosome/drug effects , Centrosome/metabolism , Drug Resistance, Neoplasm/drug effects , Extracellular Matrix Proteins/deficiency , Female , Fibronectins/metabolism , Gene Silencing/drug effects , Humans , Integrins/metabolism , Mitosis/drug effects , Models, Biological , Ovarian Neoplasms/pathology , Protein Transport/drug effects , Recombinant Proteins/metabolism , Transforming Growth Factor beta/deficiency , Tubulin/metabolismABSTRACT
Plasmid R1 inhibits growth of bacteria by synthesizing an inhibitor of cell proliferation, Kid, and a neutralizing antidote, Kis, which binds tightly to the toxin. Here we report that this toxin and antidote, which have evolved to function in bacteria, also function efficiently in a wide range of eukaryotes. Kid inhibits cell proliferation in yeast, Xenopus laevis and human cells, whilst Kis protects. Moreover, we show that Kid triggers apoptosis in human cells. These effects can be regulated in vivo by modulating the relative amounts of antidote and toxin using inducible eukaryotic promoters for independent transcriptional control of their genes. These findings allow highly regulatable, selective killing of eukaryotic cells, and could be applied to eliminate cancer cells or specific cell lineages in development.
