It is Election Day here in the US, which means that some of us need stress relief until the results are tallied. So, maybe you can imagine the graceful membrane dynamics of a cell and let their lava-lamp-like groove lull you into a happy place. Today’s image is from a paper describing the regulation of caveola biogenesis.
Caveolae are small invaginations on a cell’s plasma membrane that play important roles in cell signaling and endocytosis (the uptake of material into a cell). Caveolae depend on proteins called caveolins, but the details of caveola biogenesis are not completely understood. A recent paper describes results showing the importance of phosphorylation of Caveolin-1 (Cav1) in the formation of caveolae. Phosphorylation is the addition of a phosphate group to a protein, which functions as a molecular switch to change the protein’s activity. Joshi and colleagues found that the phosphorylation of Cav1 induces a feedback loop that links together mechanical stress on the cell, caveola biogenesis, and focal adhesion regulation at the cell’s membrane. These results place Cav1 on a list of critical proteins that help a cell respond to mechanical stress. In the images above, mutations of Cav1 that mimic phosphorylation (Cav1Y14R and Cav1Y14D) cause the formation of more caveolae and caveolae clusters (arrows and asterisks) than control cells (Cav1WT).
Joshi, B., Bastiani, M., Strugnell, S., Boscher, C., Parton, R., & Nabi, I. (2012). Phosphocaveolin-1 is a mechanotransducer that induces caveola biogenesis via Egr1 transcriptional regulation originally published in the Journal of Cell Biology, 199 (3), 425-435 DOI: 10.1083/jcb.201207089
Phosphorylation serves as a molecular switch, and the combinations of different proteins phosphorylated or dephosphorylated at any given time is mind-numbing. Phosphorylation caused one of many “Holy crap, cells are amazing!” moments in college as I realized how the regulation within a cell can be so complex. Today’s image is from a study that looks at the regulation of phosphorylation of a polarity protein.
Protein kinase C (PKC) is a family of kinases, one of which is the well-studied polarity protein atypical PKC (aPKC). These kinases must be phosphorylated before their catalytic domain is activated. The protein PDK1 serves to phosphorylate and activate newly-made PKC proteins, and a recent paper reveals that it can also phosphorylate older PKC proteins that have been since dephosphorylated, seen as a “rescue” of activity. Mashukova and colleagues also found that PDK1 is localized in membrane compartments on the apical side of some epithelial cells in close proximity to intermediate filaments, suggesting a new signaling function in these membrane compartments (endosomes). In the images above, epithelial cells have PDK1 (red) localized to the apical pole of the cells, where intermediate filaments (green) are found.
Mashukova, A., Forteza, R., Wald, F., & Salas, P. (2012). PDK1 in apical signaling endosomes participates in the rescue of the polarity complex atypical PKC by intermediate filaments in intestinal epithelia Molecular Biology of the Cell, 23 (9), 1664-1674 DOI: 10.1091/mbc.E11-12-0988
