HIGHLIGHTS from MBoC

The Editorial Board of Molecular Biology of the Cell has highlighted the following articles from the September 2016 issues. From among the many fine articles in the journal, the Board

The internalization of macromolecules from the extracellular environment is critical for the normal growth and development of all cells. Components of the endocytic machinery direct this process and must bind and bend the relatively flat surface of the cell to generate highly curved transport carriers. In this image, tubulation of synthetic liposomes is observed upon incubation with a new membrane binding and bending module, the EH domain of the endocytic scaffolding protein Eps15. Wang et al. (Mol. Biol. Cell 27, 2675–2687) demonstrate that membrane bending mediated by Eps15 functions in concert with another factor, Fcho1, to initially sculpt endocytic transport carriers. (Image: Michael Hanna and Anjon Audhya, University of Wisconsin, Madison)

The internalization of macromolecules from the extracellular environment is critical for the normal growth and development of all cells. Components of the endocytic machinery direct this process and must bind and bend the relatively flat surface of the cell to generate highly curved transport carriers. In this image, tubulation of synthetic liposomes is observed upon incubation with a new membrane binding and bending module, the EH domain of the endocytic scaffolding protein Eps15. Wang et al. (Mol. Biol. Cell 27, 2675–2687) demonstrate that membrane bending mediated by Eps15 functions in concert with another factor, Fcho1, to initially sculpt endocytic transport carriers. (Image: Michael Hanna and Anjon Audhya, University of Wisconsin, Madison)

selects for these Highlights articles that are of broad interest and significantly advance knowledge or provide new concepts or approaches that extend our understanding.

Ribosomal proteins produced in excess are degraded by the ubiquitin–proteasome system
Min-Kyung Sung, Justin M. Reitsma, Michael J. Sweredoski, Sonja Hess, and Raymond J. Deshaies
Overexpression of ribosomal proteins in yeast is prevented by ubiquitination of unassembled ribosomal proteins in the nucleus and/or nucleolus followed by proteasome-dependent degradation. Brief inhibition of the proteasome causes strong accumulation of multiple ribosomal proteins in an insoluble fraction, suggesting that this is a general phenomenon.
Mol. Biol. Cell 27 (17), 2642–2652

AMPK activity regulates trafficking of mitochondria to the leading edge during cell migration and matrix invasion
Brian Cunniff, Andrew J. McKenzie, Nicholas H. Heintz, and Alan K. Howe
Mitochondria infiltrate leading edge lamellipodia, increasing local mitochondrial mass and relative ATP concentration. AMPK regulates infiltration of mitochondria into the leading edge of 2D lamellipodia and 3D invadopodia, coupling local metabolic sensing to subcellular targeting of mitochondria during cell movement.
Mol. Biol. Cell 27 (17), 2662–2674

Eps15 membrane-binding and -bending activity acts redundantly with Fcho1 during clathrin-mediated endocytosis
Lei Wang, Adam Johnson, Michael Hanna, and Anjon Audhya
Clathrin-mediated endocytosis involves a network of proteins that direct cargo capture while simultaneously facilitating membrane remodeling. Eps15 is a critical factor that binds and bends membranes and acts redundantly with Fcho1 to ensure clathrin lattice stability during the initial stages of plasma membrane invagination.
Mol. Biol. Cell 27 (17), 2675–2687

Cell migration involves complex coordination of localized biochemical processes, many of which are energy-expensive. Shown is a color-coded image of mitochondrial flux in an ovarian cancer cell expressing a fluorescent mitochondrial marker as the cell migrates through a three-dimensional extracellular matrix. To make the image, each frame of a time-lapse live-cell movie was assigned a different hue on the color spectrum from indigo (first time point) to red (last time point), and these images were overlaid to illustrate the infiltration of mitochondria into the invasive leading edge. Cunniff, McKenzie, et al. (Mol. Biol. Cell 27, 2662–2674) detail this mitochondrial flux and show that it is controlled by localized activation of a signaling pathway that senses subcellular changes in energy status. These observations couple localized cellular energy demand to the subcellular targeting of mitochondria during cell movement. (Image: Alan K. Howe, University of Vermont)

Cell migration involves complex coordination of localized biochemical processes, many of which are energy-expensive. Shown is a color-coded image of mitochondrial flux in an ovarian cancer cell expressing a fluorescent mitochondrial marker as the cell migrates through a three-dimensional extracellular matrix. To make the image, each frame of a time-lapse live-cell movie was assigned a different hue on the color spectrum from indigo (first time point) to red (last time point), and these images were overlaid to illustrate the infiltration of mitochondria into the invasive leading edge. Cunniff, McKenzie, et al. (Mol. Biol. Cell 27, 2662–2674) detail this mitochondrial flux and show that it is controlled by localized activation of a signaling pathway that senses subcellular changes in energy status. These observations couple localized cellular energy demand to the subcellular targeting of mitochondria during cell movement. (Image: Alan K. Howe, University of Vermont)

Detection of protein–protein interactions at the septin collar in Saccharomyces cerevisiae using a tripartite split-GFP system
Gregory C. Finnigan, Angela Duvalyan, Elizabeth N. Liao, Aspram Sargsyan, and Jeremy Thorner
A tripartite split-GFP system faithfully reports the order of the subunits in septin hetero-octamers (and thus can serve as a “molecular ruler”), conversely yields little or no false signal even with very highly expressed cytosolic proteins, and detects authentic interactions of other cellular proteins that are bona fide septin-binding proteins.
Mol. Biol. Cell 27 (17), 2708–2725

Interaction of Gcn4 with target gene chromatin is modulated by proteasome function
Gregory C. Howard and William P. Tansey
The yeast transcription factor Gcn4 requires a ubiquitin ligase and the proteasome to function. Inhibiting proteasome function prevents the interaction of Gcn4 with target gene chromatin, and this activity is suppressed by inactivation of the ubiquitin-selective chaperone Cdc48. Thus proteolysis of Gcn4 is not required for its function.
Mol. Biol. Cell 27 (17), 2735–2741

TSSC1 is novel component of the endosomal retrieval machinery
David C. Gershlick, Christina Schindler, Yu Chen, and Juan S. Bonifacino
A previously uncharacterized WD40 domain–containing protein named TSSC1 is shown to interact with the GARP and EARP tethering complexes, promoting retrograde transport of Shiga toxin from endosomes to the TGN, as well as recycling internalized transferrin from endosomes to the plasma membrane.
Mol. Biol. Cell 27 (18), 2867–2878

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