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The yeast Batten disease orthologue Btn1 controls endosome-Golgi retrograde transport via SNARE assembly.

Kama R, Kanneganti V, Ungermann C, Gerst JE - J. Cell Biol. (2011)

Bottom Line: Specifically, BTN1 overexpression and deletion have opposing effects on phosphorylation of the Sed5 target membrane SNARE, on Golgi SNARE assembly, and on Golgi integrity.Although Btn1 does not interact physically with SNAREs, it regulates Sed5 phosphorylation by modulating Yck3, a palmitoylated endosomal kinase.Correspondingly, deletion of YCK3 mimics that of BTN1 or BTN2 with respect to LE-Golgi retrieval.

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Affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.

ABSTRACT
The human Batten disease gene CLN3 and yeast orthologue BTN1 encode proteins of unclear function. We show that the loss of BTN1 phenocopies that of BTN2, which encodes a retromer accessory protein involved in the retrieval of specific cargo from late endosomes (LEs) to the Golgi. However, Btn1 localizes to Golgi and regulates soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE) function to control retrograde transport. Specifically, BTN1 overexpression and deletion have opposing effects on phosphorylation of the Sed5 target membrane SNARE, on Golgi SNARE assembly, and on Golgi integrity. Although Btn1 does not interact physically with SNAREs, it regulates Sed5 phosphorylation by modulating Yck3, a palmitoylated endosomal kinase. This may involve modification of the Yck3 lipid anchor, as substitution with a transmembrane domain suppresses the deletion of BTN1 and restores trafficking. Correspondingly, deletion of YCK3 mimics that of BTN1 or BTN2 with respect to LE-Golgi retrieval. Thus, Btn1 controls retrograde sorting by regulating SNARE phosphorylation and assembly, a process that may be adversely affected in Batten Disease patients.

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A model for the control of Sed5 phosphorylation and LE–Golgi transport by Btn1 and Yck3. Yif1 is in the trans-Golgi in WT cells but delocalizes to the LE in cells lacking either BTN1 or YCK3. Thus, Btn1 and Yck3 mediate Yif1 retrieval. Sed5 is a Golgi SNARE that undergoes a phosphorylation/dephosphorylation cycle important for its localization and function (Weinberger et al., 2005). Btn1 regulates Yck3 kinase function, resulting in Sed5 phosphorylation either directly by Yck3 (as shown) or indirectly through another kinase (not depicted). Sed5 phosphorylation and dephosphorylation alter SNARE assembly in a manner that regulates retrograde transport, resulting in the retrieval of Yif1 to the Golgi. The phosphatase that dephosphorylates Sed5 is unknown but whose function must be coordinated with Yck3 to control SNARE assembly.
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fig7: A model for the control of Sed5 phosphorylation and LE–Golgi transport by Btn1 and Yck3. Yif1 is in the trans-Golgi in WT cells but delocalizes to the LE in cells lacking either BTN1 or YCK3. Thus, Btn1 and Yck3 mediate Yif1 retrieval. Sed5 is a Golgi SNARE that undergoes a phosphorylation/dephosphorylation cycle important for its localization and function (Weinberger et al., 2005). Btn1 regulates Yck3 kinase function, resulting in Sed5 phosphorylation either directly by Yck3 (as shown) or indirectly through another kinase (not depicted). Sed5 phosphorylation and dephosphorylation alter SNARE assembly in a manner that regulates retrograde transport, resulting in the retrieval of Yif1 to the Golgi. The phosphatase that dephosphorylates Sed5 is unknown but whose function must be coordinated with Yck3 to control SNARE assembly.

Mentions: Because Btn1 is not a kinase, it must be indirectly involved in Sed5 phosphorylation. Two pieces of evidence suggested that Yck3 might be involved. First, mammalian CLN3 was suggested to function as a palmitoyl protein desaturase (Narayan et al., 2006, 2008). Second, Yck3 is a palmitoylated endosome- and vacuole-associated casein kinase involved in protein sorting to the vacuole (Sun et al., 2004; LaGrassa and Ungermann, 2005). Moreover, although Yck3 shares essential functions with a paralog, Hrr25 (Wang et al., 1996), and is able to suppress deletions in homologues that function primarily at the plasma membrane (e.g., Yck1 and Yck2; Sun et al., 2004), it also phosphorylates proteins involved in vacuole protein transport, such as Vps41 and Vam3 (LaGrassa and Ungermann, 2005; Brett et al., 2008). We examined Sed5 phosphorylation in cells expressing an inducible form of YCK3 and found that this t-SNARE was underphosphorylated after the turn-off of expression (Fig. 5 A, right). Thus, Yck3 is a candidate kinase for Sed5 phosphorylation. Moreover, the deletion of YCK3 resulted in strong defects in LE–Golgi sorting (Fig. 5, B–D), which parallel those seen in btn1Δ and btn2Δ cells (Fig. 1 and Tables S1 and S2). This strengthens the idea that Yck3 is involved with Btn1 function, although Sed5 may not be the only substrate involved in the regulation of LE–Golgi sorting. A model for the control of Sed5 and LE–Golgi sorting by Btn1 and Yck3 is shown in Fig. 7.


The yeast Batten disease orthologue Btn1 controls endosome-Golgi retrograde transport via SNARE assembly.

Kama R, Kanneganti V, Ungermann C, Gerst JE - J. Cell Biol. (2011)

A model for the control of Sed5 phosphorylation and LE–Golgi transport by Btn1 and Yck3. Yif1 is in the trans-Golgi in WT cells but delocalizes to the LE in cells lacking either BTN1 or YCK3. Thus, Btn1 and Yck3 mediate Yif1 retrieval. Sed5 is a Golgi SNARE that undergoes a phosphorylation/dephosphorylation cycle important for its localization and function (Weinberger et al., 2005). Btn1 regulates Yck3 kinase function, resulting in Sed5 phosphorylation either directly by Yck3 (as shown) or indirectly through another kinase (not depicted). Sed5 phosphorylation and dephosphorylation alter SNARE assembly in a manner that regulates retrograde transport, resulting in the retrieval of Yif1 to the Golgi. The phosphatase that dephosphorylates Sed5 is unknown but whose function must be coordinated with Yck3 to control SNARE assembly.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3198160&req=5

fig7: A model for the control of Sed5 phosphorylation and LE–Golgi transport by Btn1 and Yck3. Yif1 is in the trans-Golgi in WT cells but delocalizes to the LE in cells lacking either BTN1 or YCK3. Thus, Btn1 and Yck3 mediate Yif1 retrieval. Sed5 is a Golgi SNARE that undergoes a phosphorylation/dephosphorylation cycle important for its localization and function (Weinberger et al., 2005). Btn1 regulates Yck3 kinase function, resulting in Sed5 phosphorylation either directly by Yck3 (as shown) or indirectly through another kinase (not depicted). Sed5 phosphorylation and dephosphorylation alter SNARE assembly in a manner that regulates retrograde transport, resulting in the retrieval of Yif1 to the Golgi. The phosphatase that dephosphorylates Sed5 is unknown but whose function must be coordinated with Yck3 to control SNARE assembly.
Mentions: Because Btn1 is not a kinase, it must be indirectly involved in Sed5 phosphorylation. Two pieces of evidence suggested that Yck3 might be involved. First, mammalian CLN3 was suggested to function as a palmitoyl protein desaturase (Narayan et al., 2006, 2008). Second, Yck3 is a palmitoylated endosome- and vacuole-associated casein kinase involved in protein sorting to the vacuole (Sun et al., 2004; LaGrassa and Ungermann, 2005). Moreover, although Yck3 shares essential functions with a paralog, Hrr25 (Wang et al., 1996), and is able to suppress deletions in homologues that function primarily at the plasma membrane (e.g., Yck1 and Yck2; Sun et al., 2004), it also phosphorylates proteins involved in vacuole protein transport, such as Vps41 and Vam3 (LaGrassa and Ungermann, 2005; Brett et al., 2008). We examined Sed5 phosphorylation in cells expressing an inducible form of YCK3 and found that this t-SNARE was underphosphorylated after the turn-off of expression (Fig. 5 A, right). Thus, Yck3 is a candidate kinase for Sed5 phosphorylation. Moreover, the deletion of YCK3 resulted in strong defects in LE–Golgi sorting (Fig. 5, B–D), which parallel those seen in btn1Δ and btn2Δ cells (Fig. 1 and Tables S1 and S2). This strengthens the idea that Yck3 is involved with Btn1 function, although Sed5 may not be the only substrate involved in the regulation of LE–Golgi sorting. A model for the control of Sed5 and LE–Golgi sorting by Btn1 and Yck3 is shown in Fig. 7.

Bottom Line: Specifically, BTN1 overexpression and deletion have opposing effects on phosphorylation of the Sed5 target membrane SNARE, on Golgi SNARE assembly, and on Golgi integrity.Although Btn1 does not interact physically with SNAREs, it regulates Sed5 phosphorylation by modulating Yck3, a palmitoylated endosomal kinase.Correspondingly, deletion of YCK3 mimics that of BTN1 or BTN2 with respect to LE-Golgi retrieval.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.

ABSTRACT
The human Batten disease gene CLN3 and yeast orthologue BTN1 encode proteins of unclear function. We show that the loss of BTN1 phenocopies that of BTN2, which encodes a retromer accessory protein involved in the retrieval of specific cargo from late endosomes (LEs) to the Golgi. However, Btn1 localizes to Golgi and regulates soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE) function to control retrograde transport. Specifically, BTN1 overexpression and deletion have opposing effects on phosphorylation of the Sed5 target membrane SNARE, on Golgi SNARE assembly, and on Golgi integrity. Although Btn1 does not interact physically with SNAREs, it regulates Sed5 phosphorylation by modulating Yck3, a palmitoylated endosomal kinase. This may involve modification of the Yck3 lipid anchor, as substitution with a transmembrane domain suppresses the deletion of BTN1 and restores trafficking. Correspondingly, deletion of YCK3 mimics that of BTN1 or BTN2 with respect to LE-Golgi retrieval. Thus, Btn1 controls retrograde sorting by regulating SNARE phosphorylation and assembly, a process that may be adversely affected in Batten Disease patients.

Show MeSH
Related in: MedlinePlus