A Mammalian Homolog of Drosophila Tumorous Imaginal Discs, Tid1, Mediates Agrin Signaling at the Neuromuscular Junction

Abstract

Summary Motoneuron-derived agrin clusters nicotinic acetylcholine receptors (AChRs) in mammalian muscle cells. We used two-hybrid screens to identify a protein, tumorous imaginal discs (Tid1), that binds to the cytoplasmic domain of muscle-specific kinase (MuSK), a major component of the agrin receptor. Like MuSK, Tid1 colocalizes with AChRs at developing, adult and denervated motor endplates. Knockdown of Tid1 by short hairpin RNA (shRNA) in skeletal muscle fibers dispersed synaptic AChR clusters and impaired neuromuscular transmission. In cultured myotubes, Tid1 knockdown inhibited AChR clustering, as well as agrin-induced activation of the Rac and Rho small GTPases and tyrosine phosphorylation of the AChR, without affecting MuSK activation. Tid1 knockdown also decreased Dok-7-induced clustering of AChRs. Overexpression of the N-terminal half of Tid1 induced agrin- and MuSK-independent phosphorylation and clustering of AChRs. These results demonstrate that Tid1 is an essential component of the agrin signaling pathway, crucial for synaptic development.

Essential Role of TID1 in Maintaining Mitochondrial Membrane Potential Homogeneity and Mitochondrial DNA Integrity

“…When ATP synthesis is inhibited, TID1 is recruited to a detergent-resistant fraction together with aggregates of complex I and mtDNA is lost. triggered apoptosis (22), and only TID1-S clusters acetylcholine receptors, leading to efficient synaptic transmission in neuromuscular junctions (26). Our data provide evidence that in mitochondria, the TID1-S and TID1-L isoforms are also functionally distinct.…”

“…S13 in the supplemental material). Interestingly, a previous report indicated that the Nterminal half (amino acids 1 to 222) of the TID1 protein is sufficient to induce neuronal acetylcholine receptor cluster clustering, suggesting that the C terminus is dispensable for its activity (26).…”

“…In mammalian cells, HSPA9/mortalin is the only mitochondrial Hsp70 family member and was proposed to function with TID1 as its cochaperone (22). Two TID1 mRNA splice forms that encode TID1 long and short isoforms which act as DnaJ cochaperones in the cytosol exist (23)(24)(25)(26) and are processed into mature forms following import into the mitochondrial matrix. Tid1-knockout mice die between embryonic day 4.5 (e4.5) and e7.5, demonstrating a requirement for Tid1 for normal development (27).…”

To build a synapse: signaling pathways in neuromuscular junction assembly

“…As discussed above, Musk activity is regulated by Dok7 and Lrp4. Musk also interacts with tumorous imaginal discs (Tid1; also known as Dnaja3), which is necessary for Dok7 binding to Musk in response to agrin (Linnoila et al, 2008). Upon activation, Musk becomes rapidly internalized, which is required for AChR clustering (Zhu et al, 2008).…”

Tid1, the Mammalian Homologue of Drosophila Tumor Suppressor Tid56, Mediates Macroautophagy by Interacting with Beclin1-containing Autophagy Protein Complex

“…Analysis of the subcellular localization of Tid1 indicates that this DnaJ protein resides predominantly in the mitochondria (26). However, studies have also shown that Tid1 interacts with vast amounts of cytoplasmic and plasma membrane-bound cellular and viral proteins (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16).…”