The Retrieval Function of the KDEL Receptor Requires PKA Phosphorylation of Its C-Terminus

Department of Cell Biology, Faculty of Biology, University of Seville, 41012 Seville, Spain.
Molecular Biology of the Cell (Impact Factor: 4.47). 11/2003; 14(10):4114-25. DOI: 10.1091/mbc.E03-04-0194
Source: PubMed


The KDEL receptor is a Golgi/intermediate compartment-located integral membrane protein that carries out the retrieval of escaped ER proteins bearing a C-terminal KDEL sequence. This occurs throughout retrograde traffic mediated by COPI-coated transport carriers. The role of the C-terminal cytoplasmic domain of the KDEL receptor in this process has been investigated. Deletion of this domain did not affect receptor subcellular localization although cells expressing this truncated form of the receptor failed to retain KDEL ligands intracellularly. Permeabilized cells incubated with ATP and GTP exhibited tubular processes-mediated redistribution from the Golgi area to the ER of the wild-type receptor, whereas the truncated form lacking the C-terminal domain remained concentrated in the Golgi. As revealed with a peptide-binding assay, this domain did not interact with both coatomer and ARF-GAP unless serine 209 was mutated to aspartic acid. In contrast, alanine replacement of serine 209 inhibited coatomer/ARF-GAP recruitment, receptor redistribution into the ER, and intracellular retention of KDEL ligands. Serine 209 was phosphorylated by both cytosolic and recombinant protein kinase A (PKA) catalytic subunit. Inhibition of endogenous PKA activity with H89 blocked Golgi-ER transport of the native receptor but did not affect redistribution to the ER of a mutated form bearing aspartic acid at position 209. We conclude that PKA phosphorylation of serine 209 is required for the retrograde transport of the KDEL receptor from the Golgi complex to the ER from which the retrieval of proteins bearing the KDEL signal depends.

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    • "Indeed, our identification of null mutations in the single Drosophila KdelR will allow for more direct tests for a role for the KdelR in inducing autophagy in neurodegenerative disease models [39] and in regulating cargo flux through the Golgi [40]. The null mutations can also be used to clarify the importance of post-translational modifications on Kdel-R localization and activity [41]. "
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    • "Following an increase in the intracellular levels of cAMP, the ARF proteins redistribute from the cytosol to the Golgi complex in intact cells (Martin et al. 2000). Protein kinase A also phosphorylates a COPI-binding motif on the C-terminal tail of the KDELR, which is necessary for retrograde transport of the KDELR itself (Cabrera et al. 2003) in its control of the recycling of important ER-resident proteins (e.g. ER chaperones) (Pelham 1991). "
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    • "A machinery component of COPI vesicles with another dilysine motif is the seven-helix transmembrane protein KDEL receptor that functions as a transmembrane adaptor. Its cytosolic tail interacts with coatomer via a KKXSXXX signal, active only when its serine residue is phosphorylated (Cabrera et al. 2003), whereas its luminal part interacts with soluble proteins that harbor a C-terminal KDEL-sequence (Lewis and Pelham 1992). As a result, KDEL-proteins are included into COPI vesicles and retrieved to the ER (Pelham 1991; Majoul et al. 1998), where they dissociate from the KDEL receptor, probably because of a difference of pH between Golgi and ER (Wilson et al. 1993). "
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