Dynamic interaction of BiP and ER stress transducers in the unfolded-protein response

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PERK and IRE1 are type-I transmembrane protein kinases that reside in the endoplasmic reticulum (ER) and transmit stress signals in response to perturbation of protein folding. Here we show that the lumenal domains of these two proteins are functionally interchangeable in mediating an ER stress response and that, in unstressed cells, both lumenal domains form a stable complex with the ER chaperone BiP. Perturbation of protein folding promotes reversible dissociation of BiP from the lumenal domains of PERK and IRE1. Loss of BiP correlates with the formation of high-molecular-mass complexes of activated PERK or IRE1, and overexpression of BiP attenuates their activation. These findings are consistent with a model in which BiP represses signalling through PERK and IRE1 and protein misfolding relieves this repression by effecting the release of BiP from the PERK and IRE1 lumenal domains.

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Figure 1: PERK forms a complex with BiP in unstressed cells.
Figure 2: Functional similarities of the lumenal domains of PERK and IRE1.
Figure 3: ER stress leads to dissociation of the BiP–PERK and BiP–IRE1α complexes.
Figure 4: BiP reassociates with PERK and IRE1α upon removal of ER stress.
Figure 5: BiP binding and activation of stress-signal transducers in BiP-overexpressing CHO cells.
Figure 6: ER-stress-induced formation of high-molecularmass complexes containing PERK or IRE1α but lacking BiP.
Figure 7: Oligomerization-induced activation of PERK kinase in vivo.


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We thank G. Kreibich for the anti-ribophorin antiserum, D. Littman for CD4 cDNA and monoclonal antibody, R. Kaufman and A. Dorner for CHO.BiPoe cells, M. A. Gawinowicz for mass spectroscopy and J-P. Simon for help with glycerol gradients. This work was supported by NIH grants (ES08681 and DK47119) to D.R., National Research Service award (NRSA) to H.P.H. and EMBO and Human Frontier Science programme awards to A.B. D.R. is a Stephen Birnbaum Scholar of the Leukaemia Society of America.

Correspondence and requests for materials should be addressed to D.R.

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Correspondence to David Ron.

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