Lee IC, etal., J Biol Chem. 2014 Sep 26;289(39):26989-7003. doi: 10.1074/jbc.M114.588079. Epub 2014 Aug 8.
Myotonic dystrophy kinase-related Cdc42-binding kinase (MRCK) has been shown to localize to the lamella of mammalian cells through its interaction with an adaptor protein, leucine repeat adaptor protein 35a (LRAP35a), which links it with myosin 18A (MYO18A) for activation of the lamellar actomyosin
network essential for cell migration. Here, we report the identification of another adaptor protein LRAP25 that mediates MRCK association with LIM kinase 1 (LIMK1). The lamellipodium-localized LRAP25-MRCK complex is essential for the regulation of local LIMK1 and its downstream F-actin regulatory factor cofilin. Functionally, inhibition of either MRCK or LRAP25 resulted in a marked suppression of LIMK1 activity and down-regulation of cofilin phosphorylation in response to aluminum fluoride induction in B16-F1 cells, which eventually resulted in deregulation of lamellipodial F-actin and reorganization of cytoskeletal structures causing defects in cell polarization and motility. These biochemical and functional characterizations thus underline the functional relevance of the LRAP25-MRCK complex in LIMK1-cofilin signaling and the importance of LRAP adaptors as key determinants of MRCK cellular localization and downstream specificities.
Williams syndrome (WS) is a complex neurodevelopmental disorder arising from a microdeletion at Chr band 7q11.23, which results in a hemizygous condition for a number of genes. Within this region we have completely characterized 200 kb containing the genes LIMK1
, WBSCR1, and RFC2. Evidence was also found for WBSCR5 in this region, but not the previously proposed genes WSCR2 and WSCR6. The syntenic region in mouse was also sequenced (115 kb) and characterized, and a comparative sequence analysis with a percent identity plot (PIP) easily allowed us to identify coding exons. This genomic region is GC rich (50.1% human, 49.9% mouse) and contains an unusually high abundance of repetitive elements consisting primarily of Alu (45.4%, one of the highest levels identified to date) in human, and the B family of SINES (30.6% of the total sequence) in mouse. WBSCR1 corresponds to eukaryotic initiation factor 4H, identified in rabbit, and is herein found to be constitutively expressed in both human and mouse, with two RNA and protein products formed (exon 5 is alternatively spliced). The transcription pattern of WBSCR5 was also examined and discussed along with its putative amino acid sequence.
In this study, we examined the subcellular distribution and functions of LIMK1 in developing neurons. Confocal microscopy, subcellular fractionation, and expression of several epitope-tagged LIMK1 constructs revealed that ... (more)
pan style='font-weight:700;'>LIMK1 is enriched in the Golgi apparatus and growth cones, with the LIM domain required for Golgi localization and the PDZ domain for its presence at neuritic tips. Overexpression of wild-type LIMK1 suppresses the formation of trans-Golgi derived tubules, and prevents cytochalasin D-induced Golgi fragmentation, whereas that of a kinase-defective mutant has the opposite effect. Transfection of wild-type LIMK1 accelerates axon formation and enhances the accumulation of Par3/Par6, insulin-like growth factor (IGF)1 receptors, and neural cell adhesion molecule (NCAM) at growth cones, while inhibiting the Golgi export of synaptophysin-containing vesicles. These effects were dependent on the Golgi localization of LIMK1, paralleled by an increase in cofilin phosphorylation and phalloidin staining in the region of the Golgi apparatus, and prevented by coexpression of constitutive active cofilin. The long-term overexpression of LIMK1 produces growth cone collapse and axon retraction, an effect that is dependent on its growth cone localization. Together, our results suggest an important role for LIMK1 in axon formation that is related with its ability to regulate Golgi dynamics, membrane traffic, and actin cytoskeletal organization.
Liu A, etal., J Cell Biol. 2016 Feb 15;212(4):449-63. doi: 10.1083/jcb.201509023.
Neuroligin (NLG) 1 is important for synapse development and function, but the underlying mechanisms remain unclear. It is known that at least some aspects of NLG1 function are independent of the presynaptic neurexin, suggesting that the C-terminal domain (CTD) of NLG1 may be sufficient for synaptic
regulation. In addition, NLG1 is subjected to activity-dependent proteolytic cleavage, generating a cytosolic CTD fragment, but the significance of this process remains unknown. In this study, we show that the CTD of NLG1 is sufficient to (a) enhance spine and synapse number, (b) modulate synaptic plasticity, and (c) exert these effects via its interaction with spine-associated Rap guanosine triphosphatase-activating protein and subsequent activation of LIM-domain protein kinase 1/cofilin-mediated actin reorganization. Our results provide a novel postsynaptic mechanism by which NLG1 regulates synapse development and function.
