Liprin-a and actin remodelling

  • Published 2012


Temporal and spatial remodelling of the actin cytoskeleton is important for cell morphology and migration. The mammalian homologue of Diaphanous (mDia) – an actin nucleator that forms unbranched actin filaments – is an effector of the small GTPase RhoA, which itself is a key regulator of actin remodelling. But how is mDia activity regulated in cells? To answer this question, Shuh Narumiya and colleagues (p. 108) have been looking for mDia-binding proteins in mouse brain lysates using an N-terminal mDia1 fragment as bait. mDia is autoregulated through an intra-molecular interaction between an N-terminal Dia-inhibitory domain (DID) and a C-terminal Dia autoregulatory domain (DAD). Binding of GTP-bound RhoA to mDia disrupts this intra-molecular interaction and activates mDia. In their pull-down assay, the authors identify Liprin-a (an interacting protein of the leukocyte common antigen-related family of receptor protein tyrosine phosphatases) as an mDia-binding protein. Liprin-a, they report, binds to the active form of mDia through the DID and negatively regulates the localization of mDia to the plasma membrane and the formation of actin stress fibres. Thus, they conclude, Liprin-a is a negative regulator of mDia, and further studies on this function of Liprin-a could shed new light onto the regulation of mDia-mediated actin remodelling in cells. (written by Jane Bradbury) Cajal bodies: no integrity without integrator The eukaryotic nucleus is compartmentalised into a number of functional domains, including chromosome territories and nuclear bodies. The Cajal body is one of the most prominent nuclear bodies and is thought to be the site for formation of small nuclear and small nucleolar ribonucleoprotein particles (snRNPs and snoRNPs, respectively). Although it is known that Cajal bodies contain a number of proteins, such as coilin, fibrillarin, dyskerin and Nopp140, in addition to snRNPs and snoRNPs, the mechanism underlying their formation remained unclear so far. Here, Hideaka Takata, Kei-ichi Shibahara and colleagues (p. 166) shed light on the biogenesis of these snRNA-related suborganelles by highlighting a role for the integrator complex in establishing Cajal bodies. They show that RNAi-mediated depletion of two integrator subunits (INTS4 and INTS11) results in the relocalisation of coilin to the nucleolus instead of to Cajal bodies. In addition, the Cajal body component survival of motor neuron protein (SMN) and Sm proteins localise to the cytoplasm, where they form prominent cytoplasmic granules. The authors also find that cells lacking INTS4 accumulate premature U2 snRNAs in the nucleus and conclude that the 3 -end processing activity of snRNAs by the integrator complex is crucial for the formation of completely functional Cajal bodies.

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@inproceedings{2012LiprinaAA, title={Liprin-a and actin remodelling}, author={}, year={2012} }