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  • Rockefeller University Press  (2)
  • The American Society for Biochemistry and Molecular Biology (ASBMB)  (2)
  • 1
    Publication Date: 2012-10-02
    Description: The cancer-associated loss of microRNA (miRNA) expression leads to a proliferative advantage and aggressive behavior through largely unknown mechanisms. Here, we exploit a model system that recapitulates physiological terminal differentiation and its reversal upon oncogene expression to analyze coordinated mRNA/miRNA responses. The cell cycle reentry of myotubes, forced by the E1A oncogene, was associated with a pattern of mRNA/miRNA modulation that was largely reciprocal to that induced during the differentiation of myoblasts into myotubes. The E1A-induced mRNA response was preponderantly Retinoblastoma protein (Rb)-dependent. Conversely, the miRNA response was mostly Rb-independent and exerted through tissue-specific factors and Myc. A subset of these miRNAs (miR-1, miR-34, miR-22, miR-365, miR-29, miR-145, and Let-7) was shown to coordinately target Rb-dependent cell cycle and DNA replication mRNAs. Thus, a dual level of regulation—transcriptional regulation via Rb–E2F and posttranscriptional regulation via miRNAs—confers robustness to cell cycle control and provides a molecular basis to understand the role of miRNA subversion in cancer.
    Electronic ISSN: 1540-8140
    Topics: Biology
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  • 2
    Publication Date: 2016-07-30
    Description: Amino acid permeases (AAPs) in the plasma membrane (PM) of Saccharomyces cerevisiae are responsible for the uptake of amino acids and involved in regulation of their cellular levels. Here, we report on a strong and complex module for PM association found in the C-terminal tail of AAPs. Using in silico analyses and mutational studies we found that the C-terminal sequences of Gap1, Bap2, Hip1, Tat1, Tat2, Mmp1, Sam3, Agp1, and Gnp1 are about 50 residues long, associate with the PM, and have features that discriminate them from the termini of organellar amino acid transporters. We show that this sequence (named PMasseq) contains an amphipathic α-helix and the FWC signature, which is palmitoylated by palmitoyltransferase Pfa4. Variations of PMasseq, found in different AAPs, lead to different mobilities and localization patterns, whereas the disruption of the sequence has an adverse effect on cell viability. We propose that PMasseq modulates the function and localization of AAPs along the PM. PMasseq is one of the most complex protein signals for plasma membrane association across species and can be used as a delivery vehicle for the PM.
    Print ISSN: 0021-9258
    Electronic ISSN: 1083-351X
    Topics: Biology , Chemistry and Pharmacology
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  • 3
    Publication Date: 2014-07-22
    Description: The mechanisms by which tumor cells metastasize and the role of endocytic proteins in this process are not well understood. We report that overexpression of the GTPase RAB5A, a master regulator of endocytosis, is predictive of aggressive behavior and metastatic ability in human breast cancers. RAB5A is necessary and sufficient to promote local invasion and distant dissemination of various mammary and nonmammary tumor cell lines, and this prometastatic behavior is associated with increased intratumoral cell motility. Specifically, RAB5A is necessary for the formation of invadosomes, membrane protrusions specialized in extracellular matrix (ECM) degradation. RAB5A promotes RAB4- and RABENOSYN-5–dependent endo/exocytic cycles (EECs) of critical cargos (membrane-type 1 matrix metalloprotease [MT1-MMP] and β3 integrin) required for invadosome formation in response to motogenic stimuli. This trafficking circuitry is necessary for spatially localized hepatocyte growth factor (HGF)/MET signaling that drives invasive, proteolysis-dependent chemotaxis in vitro and for conversion of ductal carcinoma in situ to invasive ductal carcinoma in vivo. Thus, RAB5A/RAB4 EECs promote tumor dissemination by controlling a proteolytic, mesenchymal invasive program.
    Electronic ISSN: 1540-8140
    Topics: Biology
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  • 4
    Publication Date: 2012-07-28
    Description: The bacterial multidrug transporter EmrE is a dual-topology membrane protein and as such is able to insert into the membrane in two opposite orientations. The functional form of EmrE is a homodimer; however, the relative orientation of the subunits in the dimer is under debate. Using EmrE variants with fixed, opposite orientations in the membrane, we now show that, although the proteins are able to form parallel dimers, an antiparallel organization of the subunits in the dimer is preferred. Blue-native PAGE analyses of intact oligomers and disulfide cross-linking demonstrate that in membranes, the proteins form parallel dimers only if no oppositely orientated partner is present. Co-expression of oppositely orientated proteins almost exclusively yields antiparallel dimers. Finally, parallel dimers can be disrupted and converted into antiparallel dimers by heating of detergent-solubilized protein. Importantly, in vivo function is correlated clearly to the presence of antiparallel dimers. Our results suggest that an antiparallel arrangement of the subunits in the dimer is more stable than a parallel organization and likely corresponds to the functional form of the protein.
    Print ISSN: 0021-9258
    Electronic ISSN: 1083-351X
    Topics: Biology , Chemistry and Pharmacology
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