Winter et al.: one isoform of the protein anchors mitochondria to the cytoskeleton and keeps these organelles in shape, and may also create a platform for signaling.
Plectin is a “cytolinker” protein responsible for connecting intermediate filaments with, among other things, actin microfilaments, microtubules, and myosin motors. Its versatility arises from alternative splicing—almost a dozen isoforms are known, which differ at their N termini, affecting the substrates to which they can attach. One isoform, P1b, has been found targeted to mitochondria, but the significance of this linkage has been unclear.
The authors have now found that P1b links mitochondria to the intermediate filament protein, vimentin. P1b colocalized with vimentin, and loss of P1b reduced the amount of vimentin in mitochondrial extracts. Loss of P1b also dramatically altered mitochondrial shape, increasing the number of mitochondria that were highly elongated. Elongation was not caused by alterations in mitochondrial membrane potential, mass, or fusion dynamics. But it may have resulted from a reduction in protein kinase C-δ activation, as this was apparent in cells that lacked P1b, through unknown mechanisms. PKC-δ promotes mitochondrial fission, and the authors suggest that intermediate filament–linked P1b may serve as a scaffold for recruiting PKC-δ, and perhaps other signaling molecules, to regulate mitochondrial fission.