Microtubule binding distinguishes dystrophin from utrophin

Abstract

Dystrophin and utrophin are highly similar proteins that both link cortical actin filaments with a complex of sarcolemmal glycoproteins, yet localize to different subcellular domains within normal muscle cells. In mdx mice and Duchenne muscular dystrophy patients, dystrophin is lacking and utrophin is consequently up-regulated and redistributed to locations normally occupied by dystrophin. Transgenic overexpression of utrophin has been shown to significantly improve aspects of the disease phenotype in the mdx mouse; therefore, utrophin up-regulation is under intense investigation as a potential therapy for Duchenne muscular dystrophy. Here we biochemically compared the previously documented microtubule binding activity of dystrophin with utrophin and analyzed several transgenic mouse models to identify phenotypes of the mdx mouse that remain despite transgenic utrophin overexpression. Our in vitro analyses revealed that dystrophin binds microtubules with high affinity and pauses microtubule polymerization, whereas utrophin has no activity in either assay. We also found that transgenic utrophin overexpression does not correct subsarcolemmal microtubule lattice disorganization, loss of torque production after in vivo eccentric contractions, or physical inactivity after mild exercise. Finally, our data suggest that exerciseinduced inactivity correlates with loss of sarcolemmal neuronal NOS localization in mdx muscle, whereas loss of in vivo torque production after eccentric contraction-induced injury is associated with microtubule lattice disorganization.

Microtubule-targeting agents augment the toxicity of DNA-damaging agents by disrupting intracellular trafficking of DNA repair proteins

“…We thus nominate these nine proteins to what should become a growing list of crucial proteins trafficking on MTs. For some of these proteins (23)(24)(25)(26), an association with or trafficking on MTs has been previously reported and the present data corroborate and extend those observations (27). We demonstrate effects consistent with our hypothesis using multiple cell lines, different methodologies, and both vincristine and paclitaxel.…”

Dystrophin's central domain forms a complex filament that becomes disorganized by in-frame deletions

“…This compartmentalization may allow dystrophin to recruit protein partners simultaneously while bound to the plasma membrane (37). In particular, the bulkiest molecules, intermediate filaments and F-actin, are recruited by the large R11-17 domain while microtubules are recruited by R20-23 (38) and due to steric hindrance, these interactions could not occur simultaneously with a straight central domain. Remarkably, these regions overlap with DMD gene mutational hotspots (exons 44 to 55) (6, 7).…”

Triadin and CLIMP-63 form a link between triads and microtubules in muscle cells

“…The triadin-CLIMP-63 protein pair is most probably not the only microtubule organizer in muscle fibers, and the creation of orthogonal grid of microtubules would be expected to require numerous other proteins. For example, dystrophin as well as the complex ankyrin-Bdynactin-4 have been proposed as being responsible for microtubule anchoring at costameres (Ayalon et al, 2008;Belanto et al, 2014;Prins et al, 2009). …”