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Complexes of Usher proteins preassemble at the endoplasmic reticulum and are required for trafficking and ER homeostasis.

Blanco-Sánchez B, Clément A, Fierro J, Washbourne P, Westerfield M - Dis Model Mech (2014)

Bottom Line: We found that the proteins are in close enough proximity to form complexes and that these complexes preassemble at the endoplasmic reticulum (ER).Defects in any one of the three USH proteins disrupt formation and trafficking of the complex and result in diminished levels of the other proteins, generalized trafficking defects and ER stress that triggers apoptosis.ER stress, thus, contributes to sensory hair cell loss and provides a new target to explore for protective therapies for USH.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.

ABSTRACT
Usher syndrome (USH), the leading cause of hereditary combined hearing and vision loss, is characterized by sensorineural deafness and progressive retinal degeneration. Mutations in several different genes produce USH, but the proximal cause of sensory cell death remains mysterious. We adapted a proximity ligation assay to analyze associations among three of the USH proteins, Cdh23, Harmonin and Myo7aa, and the microtubule-based transporter Ift88 in zebrafish inner ear mechanosensory hair cells. We found that the proteins are in close enough proximity to form complexes and that these complexes preassemble at the endoplasmic reticulum (ER). Defects in any one of the three USH proteins disrupt formation and trafficking of the complex and result in diminished levels of the other proteins, generalized trafficking defects and ER stress that triggers apoptosis. ER stress, thus, contributes to sensory hair cell loss and provides a new target to explore for protective therapies for USH.

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The Cdh23, Harmonin, Ift88 and Myo7aa protein complex preassembles at the ER. Model for assembly and trafficking of USH proteins. Under normal conditions in wild-type (WT) animals, Cadherin23, Harmonin, Ift88 and Myo7aa preassemble into a complex at the level of the ER. Interaction between Cdh23 and Myo7aa is required for Cdh23 translocation to the ERES. All four proteins are required for assembly of a functional complex. Once assembled, the complex translocates to ER exit sites (ERES), engages components of the COPII system (Sec23 and Sec13), and enters the secretory pathway where it is trafficked to the ER-Golgi intermediate complex (ERGIC) en route to final destinations. Loss-of-function mutations in cdh23, ush1c, ift88 and myo7aa disrupt assembly of the complex in various ways. RER, rough endoplasmic reticulum.
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f6-0070547: The Cdh23, Harmonin, Ift88 and Myo7aa protein complex preassembles at the ER. Model for assembly and trafficking of USH proteins. Under normal conditions in wild-type (WT) animals, Cadherin23, Harmonin, Ift88 and Myo7aa preassemble into a complex at the level of the ER. Interaction between Cdh23 and Myo7aa is required for Cdh23 translocation to the ERES. All four proteins are required for assembly of a functional complex. Once assembled, the complex translocates to ER exit sites (ERES), engages components of the COPII system (Sec23 and Sec13), and enters the secretory pathway where it is trafficked to the ER-Golgi intermediate complex (ERGIC) en route to final destinations. Loss-of-function mutations in cdh23, ush1c, ift88 and myo7aa disrupt assembly of the complex in various ways. RER, rough endoplasmic reticulum.

Mentions: The loss of Sec23 or Sec13 association with the three USH1 proteins or Ift88 in USH1 or ift88 mutants indicated that assembly of the complex is necessary for targeting the complex to the ERES and subsequent secretion. To test this interpretation further, we examined formation of the ER-Golgi intermediate complex (ERGIC), as indicated by Trappc3 labeling (Cai et al., 2007; Yu et al., 2006). In wild-type hair cells, some Trappc3 labeling overlapped with that of each of the three USH1 proteins (supplementary material Fig. S11D–F), indicating that the USH1 proteins traffic through the ERGIC. The total amount of Trappc3 labeling was reduced in all three USH1 mutants and in ift88 mutants (Fig. 5E,J,O,T,Y; supplementary material Fig. S12). This result is consistent with the trafficking defects seen by proximity labeling with Sec23 or Sec13 (Fig. 5), and further demonstrates that defects in assembly or trafficking of the complex produce a global reduction of the ERGIC. Thus, defects in Ift88 or any one of the three USH1 proteins disrupt formation of the complex, trafficking, and biogenesis of the ERGIC (Fig. 6).


Complexes of Usher proteins preassemble at the endoplasmic reticulum and are required for trafficking and ER homeostasis.

Blanco-Sánchez B, Clément A, Fierro J, Washbourne P, Westerfield M - Dis Model Mech (2014)

The Cdh23, Harmonin, Ift88 and Myo7aa protein complex preassembles at the ER. Model for assembly and trafficking of USH proteins. Under normal conditions in wild-type (WT) animals, Cadherin23, Harmonin, Ift88 and Myo7aa preassemble into a complex at the level of the ER. Interaction between Cdh23 and Myo7aa is required for Cdh23 translocation to the ERES. All four proteins are required for assembly of a functional complex. Once assembled, the complex translocates to ER exit sites (ERES), engages components of the COPII system (Sec23 and Sec13), and enters the secretory pathway where it is trafficked to the ER-Golgi intermediate complex (ERGIC) en route to final destinations. Loss-of-function mutations in cdh23, ush1c, ift88 and myo7aa disrupt assembly of the complex in various ways. RER, rough endoplasmic reticulum.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4007406&req=5

f6-0070547: The Cdh23, Harmonin, Ift88 and Myo7aa protein complex preassembles at the ER. Model for assembly and trafficking of USH proteins. Under normal conditions in wild-type (WT) animals, Cadherin23, Harmonin, Ift88 and Myo7aa preassemble into a complex at the level of the ER. Interaction between Cdh23 and Myo7aa is required for Cdh23 translocation to the ERES. All four proteins are required for assembly of a functional complex. Once assembled, the complex translocates to ER exit sites (ERES), engages components of the COPII system (Sec23 and Sec13), and enters the secretory pathway where it is trafficked to the ER-Golgi intermediate complex (ERGIC) en route to final destinations. Loss-of-function mutations in cdh23, ush1c, ift88 and myo7aa disrupt assembly of the complex in various ways. RER, rough endoplasmic reticulum.
Mentions: The loss of Sec23 or Sec13 association with the three USH1 proteins or Ift88 in USH1 or ift88 mutants indicated that assembly of the complex is necessary for targeting the complex to the ERES and subsequent secretion. To test this interpretation further, we examined formation of the ER-Golgi intermediate complex (ERGIC), as indicated by Trappc3 labeling (Cai et al., 2007; Yu et al., 2006). In wild-type hair cells, some Trappc3 labeling overlapped with that of each of the three USH1 proteins (supplementary material Fig. S11D–F), indicating that the USH1 proteins traffic through the ERGIC. The total amount of Trappc3 labeling was reduced in all three USH1 mutants and in ift88 mutants (Fig. 5E,J,O,T,Y; supplementary material Fig. S12). This result is consistent with the trafficking defects seen by proximity labeling with Sec23 or Sec13 (Fig. 5), and further demonstrates that defects in assembly or trafficking of the complex produce a global reduction of the ERGIC. Thus, defects in Ift88 or any one of the three USH1 proteins disrupt formation of the complex, trafficking, and biogenesis of the ERGIC (Fig. 6).

Bottom Line: We found that the proteins are in close enough proximity to form complexes and that these complexes preassemble at the endoplasmic reticulum (ER).Defects in any one of the three USH proteins disrupt formation and trafficking of the complex and result in diminished levels of the other proteins, generalized trafficking defects and ER stress that triggers apoptosis.ER stress, thus, contributes to sensory hair cell loss and provides a new target to explore for protective therapies for USH.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neuroscience, University of Oregon, Eugene, OR 97403, USA.

ABSTRACT
Usher syndrome (USH), the leading cause of hereditary combined hearing and vision loss, is characterized by sensorineural deafness and progressive retinal degeneration. Mutations in several different genes produce USH, but the proximal cause of sensory cell death remains mysterious. We adapted a proximity ligation assay to analyze associations among three of the USH proteins, Cdh23, Harmonin and Myo7aa, and the microtubule-based transporter Ift88 in zebrafish inner ear mechanosensory hair cells. We found that the proteins are in close enough proximity to form complexes and that these complexes preassemble at the endoplasmic reticulum (ER). Defects in any one of the three USH proteins disrupt formation and trafficking of the complex and result in diminished levels of the other proteins, generalized trafficking defects and ER stress that triggers apoptosis. ER stress, thus, contributes to sensory hair cell loss and provides a new target to explore for protective therapies for USH.

Show MeSH
Related in: MedlinePlus