Kalirin is required for BDNF-TrkB stimulated neurite outgrowth and branching

Abstract

Exogenous brain-derived neurotrophic factor (BDNF), acting through TrkB, is known to promote neurite formation and branching. This response to BDNF was eliminated by inhibition of TrkB kinase and by specific inhibition of the GEF1 domain of Kalirin, which activates Rac1. Neurons from Kalrn knockout mice were unable to activate Rac1 in response to BDNF. BDNF-triggered neurite outgrowth was abolished when Kalrn expression was reduced using shRNA that targets all of the major Kalrn isoforms, and reduced in neurons from Kalrn knockout mice. The Kalrn isoforms expressed early in development also include a GEF2 domain that activates RhoA. However, BDNF-stimulated neurite outgrowth in Kalrn knockout neurons was rescued by expression of Kalirin-7, which includes only the GEF1 domain but lacks the GEF2 domain. Dendritic morphogenesis, which requires spatially restricted, coordinated changes in the actin cytoskeleton and in the organization of microtubules, involves essential contributions from multiple Rho GEFs. Since Tiam1, another Rho GEF, is also required for BDNF-stimulated neurite outgrowth, an inhibitory fragment of Tiam1 (PHn-CC-EX) was tested and found to interfere with both Kalirin and Tiam1 GEF activity. The prolonged TrkB activation observed in response to BDNF in Kalrn knockout neurons and the altered time course and extent of ERK, CREB and Akt activation observed in the absence of Kalrn would be expected to alter the response of these neurons to other regulatory factors.

Brain Region and Isoform-Specific Phosphorylation Alters Kalirin SH2 Domain Interaction Sites and Calpain Sensitivity

“…Dora-Rac1, a FRET biosensor for Rac1, was used to evaluate Rac1 activation in cells expressing each Kal7 mutant 58, 89 . Briefly, vector encoding the Dora-Rac1 biosensor and various amounts of vector encoding Myc-tagged Kalirin or KalGEF1 were transfected into HEK293 cells.…”

“…Phosphorylated bKal7 was prepared for mass spec analysis as described for SR7:9; pY1123 was the major site identified. Based on the rosette screen and the biologically significant role played by Kalirin in TrkB signaling 58 , a subset of 12 GST-SH2 and -PTB domains were tested for their ability to bind to bKal7 phosphorylated in vitro by recombinant TrkB kinase. For Western blotting, TrkB-treated and untreated bKal7 proteins were separated on 4-12 % NuPAGE gels (Invitrogen), transferred to nitrocellulose, and probed with antibodies to phosphotyrosine (Cell Signaling), Kalirin 22 and phosphorylated TrkB /pY816 (Ab75173, Abcam).…”

Using Kalirin conditional knockout mice to distinguish its role in dopamine receptor mediated behaviors

“…Since levels of Kal9 and Kal12, which play essential roles in neurite extension and branching early in development, rise in Kal7 KO mice [29, 30], it seemed possible that changes in these isoforms could contribute to the exaggerated responses to cocaine availability or administration. If so, the response of KalSR KO mice to cocaine would be expected to differ from the response of Kal7 KO mice.…”

A Novel Long Non-coding RNA, durga Modulates Dendrite Density and Expression of kalirin in Zebrafish

“…These transcript isoforms also differs in the spatio-temporal expression pattern as seen in Kalrn7 found in the adult brain and Kalrn9 and 12 predominantly expressed during development. Kalirin protein isoforms seem to respond to a variety of signals including Nerve Growth Factor signaling through the TrkB receptor, BDNF signaling through Rac1 (Chakrabarti et al, 2005; Yan et al, 2016). It also interacts with many PDZ domain containing proteins such as PSD95 (Penzes et al, 2001).…”