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The Chlamydia pneumoniae Inclusion Membrane Protein Cpn1027 Interacts with Host Cell Wnt Signaling Pathway Regulator Cytoplasmic Activation/Proliferation-Associated Protein 2 (Caprin2).

Flores R, Zhong G - PLoS ONE (2015)

Bottom Line: Cpn1027 also co-precipitated GSK3β.We found that the C. pneumoniae-infected cells were more resistant to apoptosis induction and the anti-apoptotic activity was dependent on β-catenin.Thus, the current study suggests that the chlamydial inclusion protein Cpn1027 may be able to manipulate host Wnt signaling pathway for enhancing the chlamydial anti-apoptotic activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology & Immunology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.

ABSTRACT
We previously identified hypothetical protein Cpn1027 as a novel inclusion membrane protein that is unique to Chlamydia pneumoniae. In the current study, using a yeast-two hybrid screen assay, we identified host cell cytoplasmic activation/proliferation-associated protein 2 (Caprin2) as an interacting partner of Cpn1027. The interaction was confirmed and mapped to the C-termini of both Cpn1027 and Caprin2 using co-immunoprecipitation and GST pull-down assays. A RFP-Caprin2 fusion protein was recruited to the chlamydial inclusion and so was the endogenous GSK3β, a critical component of the β-catenin destruction complex in the Wnt signaling pathway. Cpn1027 also co-precipitated GSK3β. Caprin2 is a key regulator of the Wnt signaling pathway by promoting the recruitment of the β-catenin destruction complex to the cytoplasmic membrane in the presence of Wnt signaling while GSK3β is required for priming β-catenin for degradation in the absence of Wnt signaling. The Cpn1027 interactions with Caprin2 and GSK3β may allow C. pneumoniae to actively sequester the β-catenin destruction complex so that β-catenin is maintained even in the absence of extracellular Wnt activation signals. The maintained β-catenin can trans-activate Wnt target genes including Bcl-2, which may contribute to the chlamydial antiapoptotic activity. We found that the C. pneumoniae-infected cells were more resistant to apoptosis induction and the anti-apoptotic activity was dependent on β-catenin. Thus, the current study suggests that the chlamydial inclusion protein Cpn1027 may be able to manipulate host Wnt signaling pathway for enhancing the chlamydial anti-apoptotic activity.

No MeSH data available.


Related in: MedlinePlus

A working model for C. pneumoniae-mediated activation of the Wnt signaling transduction pathway.A. In the absence of Wnt signals, cytosolic β-catenin is degraded by a β-catenin destruction complex composed of Axin, adenomatosis polyposis coli (APC), glycogen synthase kinase 3β (GSK3β) and casein kinase 1α (CK1α). Both GSK3β and CK1α can phosphorylate β-catenin, which triggers ubiquitination and subsequent degradation of β-catenin by proteasomes. B. The Wnt signaling pathway is activated by binding of Wnt ligands, to Frizzled and LRP5/6 at the cell surface. LRP5/6 is activated by phosphorylation, which recruits the β-catenin destruction complex to the plasma membrane. The cytoplasmic activation/proliferation-associated protein 2 (Caprin2) facilitates LRP5/6 phosphorylation by GSK3β and enhances the interaction between Axin and the cytoplasmic tail of LRP5/6, which promotes the sequestration of the β-catenin destruction complex. The cytoplasmic pool of β-catenin rises and translocates into the nucleus, where it binds to the TCF/LEF family of transcription factors, displacing co-repressors Groucho and HDAC and acts as a co-activator to stimulate the transcription of anti-apoptotic, Bcl-2. C. In the C. pneumoniae AR39-infected cells, signalosomes are formed around the inclusion possibly through the chlamydial Inc protein Cpn1027 interacting with the β-catenin destruction complex, composed of Caprin2, Axin, GSK3β and CKIα resulting in the activation of the Wnt signaling transduction pathway in the absence of extracellular stimulation of Wnt. This leads to an increase in the cytoplasmic pool of β-catenin, nuclear β-catenin and membrane-associated β-catenin. The β-catenin-transactivated anti-apoptosis genes may promote the survival of the C. pneumoniae AR39-infected cells, hence the survival of AR39.
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pone.0127909.g005: A working model for C. pneumoniae-mediated activation of the Wnt signaling transduction pathway.A. In the absence of Wnt signals, cytosolic β-catenin is degraded by a β-catenin destruction complex composed of Axin, adenomatosis polyposis coli (APC), glycogen synthase kinase 3β (GSK3β) and casein kinase 1α (CK1α). Both GSK3β and CK1α can phosphorylate β-catenin, which triggers ubiquitination and subsequent degradation of β-catenin by proteasomes. B. The Wnt signaling pathway is activated by binding of Wnt ligands, to Frizzled and LRP5/6 at the cell surface. LRP5/6 is activated by phosphorylation, which recruits the β-catenin destruction complex to the plasma membrane. The cytoplasmic activation/proliferation-associated protein 2 (Caprin2) facilitates LRP5/6 phosphorylation by GSK3β and enhances the interaction between Axin and the cytoplasmic tail of LRP5/6, which promotes the sequestration of the β-catenin destruction complex. The cytoplasmic pool of β-catenin rises and translocates into the nucleus, where it binds to the TCF/LEF family of transcription factors, displacing co-repressors Groucho and HDAC and acts as a co-activator to stimulate the transcription of anti-apoptotic, Bcl-2. C. In the C. pneumoniae AR39-infected cells, signalosomes are formed around the inclusion possibly through the chlamydial Inc protein Cpn1027 interacting with the β-catenin destruction complex, composed of Caprin2, Axin, GSK3β and CKIα resulting in the activation of the Wnt signaling transduction pathway in the absence of extracellular stimulation of Wnt. This leads to an increase in the cytoplasmic pool of β-catenin, nuclear β-catenin and membrane-associated β-catenin. The β-catenin-transactivated anti-apoptosis genes may promote the survival of the C. pneumoniae AR39-infected cells, hence the survival of AR39.

Mentions: The observation that the C-terminal regions in both Cpn1027 and Caprin2 are responsible for their interactions indicates that their C-termini are accessible to each other. All chlamydial inclusion proteins possess a bi-lobed hydrophobic trans-membrane region in either their N- or C-terminal regions [19,40,41]. The Cpn1027’s bi-lobed region is localized in its N-terminus [15], suggesting that the C-terminus of Cpn1027 is exposed to the host cell cytoplasm, thus allowing the Cpn1027 C-terminus to access to the host cytoplasmic signaling protein Caprin2. It has been previously shown that the Chlamydia pneumoniae inclusion protein Cpn0585 may use its C-terminus to interact with multiple host cell Rab GTPases [9] while Cp0236 with the host NFkappaB activator 1 (Act1; ref: [22]. The C-terminus of Caprin2 is a C1q-related domain that is a homotrimer required for Caprin2 to interact with the Wnt signaling receptor complex LRP5/6 [28,42]. By interacting with the C1q-related domain of Caprin2, Cpn1027 anchored in the Chlamydia pneumoniae inclusion membrane may mimick the function of the Wnt signaling receptor for stabilizing the Caprin2 trimer and recruiting the β-catenin destruction complex around the chlamydial inclusion (Fig 5).


The Chlamydia pneumoniae Inclusion Membrane Protein Cpn1027 Interacts with Host Cell Wnt Signaling Pathway Regulator Cytoplasmic Activation/Proliferation-Associated Protein 2 (Caprin2).

Flores R, Zhong G - PLoS ONE (2015)

A working model for C. pneumoniae-mediated activation of the Wnt signaling transduction pathway.A. In the absence of Wnt signals, cytosolic β-catenin is degraded by a β-catenin destruction complex composed of Axin, adenomatosis polyposis coli (APC), glycogen synthase kinase 3β (GSK3β) and casein kinase 1α (CK1α). Both GSK3β and CK1α can phosphorylate β-catenin, which triggers ubiquitination and subsequent degradation of β-catenin by proteasomes. B. The Wnt signaling pathway is activated by binding of Wnt ligands, to Frizzled and LRP5/6 at the cell surface. LRP5/6 is activated by phosphorylation, which recruits the β-catenin destruction complex to the plasma membrane. The cytoplasmic activation/proliferation-associated protein 2 (Caprin2) facilitates LRP5/6 phosphorylation by GSK3β and enhances the interaction between Axin and the cytoplasmic tail of LRP5/6, which promotes the sequestration of the β-catenin destruction complex. The cytoplasmic pool of β-catenin rises and translocates into the nucleus, where it binds to the TCF/LEF family of transcription factors, displacing co-repressors Groucho and HDAC and acts as a co-activator to stimulate the transcription of anti-apoptotic, Bcl-2. C. In the C. pneumoniae AR39-infected cells, signalosomes are formed around the inclusion possibly through the chlamydial Inc protein Cpn1027 interacting with the β-catenin destruction complex, composed of Caprin2, Axin, GSK3β and CKIα resulting in the activation of the Wnt signaling transduction pathway in the absence of extracellular stimulation of Wnt. This leads to an increase in the cytoplasmic pool of β-catenin, nuclear β-catenin and membrane-associated β-catenin. The β-catenin-transactivated anti-apoptosis genes may promote the survival of the C. pneumoniae AR39-infected cells, hence the survival of AR39.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
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pone.0127909.g005: A working model for C. pneumoniae-mediated activation of the Wnt signaling transduction pathway.A. In the absence of Wnt signals, cytosolic β-catenin is degraded by a β-catenin destruction complex composed of Axin, adenomatosis polyposis coli (APC), glycogen synthase kinase 3β (GSK3β) and casein kinase 1α (CK1α). Both GSK3β and CK1α can phosphorylate β-catenin, which triggers ubiquitination and subsequent degradation of β-catenin by proteasomes. B. The Wnt signaling pathway is activated by binding of Wnt ligands, to Frizzled and LRP5/6 at the cell surface. LRP5/6 is activated by phosphorylation, which recruits the β-catenin destruction complex to the plasma membrane. The cytoplasmic activation/proliferation-associated protein 2 (Caprin2) facilitates LRP5/6 phosphorylation by GSK3β and enhances the interaction between Axin and the cytoplasmic tail of LRP5/6, which promotes the sequestration of the β-catenin destruction complex. The cytoplasmic pool of β-catenin rises and translocates into the nucleus, where it binds to the TCF/LEF family of transcription factors, displacing co-repressors Groucho and HDAC and acts as a co-activator to stimulate the transcription of anti-apoptotic, Bcl-2. C. In the C. pneumoniae AR39-infected cells, signalosomes are formed around the inclusion possibly through the chlamydial Inc protein Cpn1027 interacting with the β-catenin destruction complex, composed of Caprin2, Axin, GSK3β and CKIα resulting in the activation of the Wnt signaling transduction pathway in the absence of extracellular stimulation of Wnt. This leads to an increase in the cytoplasmic pool of β-catenin, nuclear β-catenin and membrane-associated β-catenin. The β-catenin-transactivated anti-apoptosis genes may promote the survival of the C. pneumoniae AR39-infected cells, hence the survival of AR39.
Mentions: The observation that the C-terminal regions in both Cpn1027 and Caprin2 are responsible for their interactions indicates that their C-termini are accessible to each other. All chlamydial inclusion proteins possess a bi-lobed hydrophobic trans-membrane region in either their N- or C-terminal regions [19,40,41]. The Cpn1027’s bi-lobed region is localized in its N-terminus [15], suggesting that the C-terminus of Cpn1027 is exposed to the host cell cytoplasm, thus allowing the Cpn1027 C-terminus to access to the host cytoplasmic signaling protein Caprin2. It has been previously shown that the Chlamydia pneumoniae inclusion protein Cpn0585 may use its C-terminus to interact with multiple host cell Rab GTPases [9] while Cp0236 with the host NFkappaB activator 1 (Act1; ref: [22]. The C-terminus of Caprin2 is a C1q-related domain that is a homotrimer required for Caprin2 to interact with the Wnt signaling receptor complex LRP5/6 [28,42]. By interacting with the C1q-related domain of Caprin2, Cpn1027 anchored in the Chlamydia pneumoniae inclusion membrane may mimick the function of the Wnt signaling receptor for stabilizing the Caprin2 trimer and recruiting the β-catenin destruction complex around the chlamydial inclusion (Fig 5).

Bottom Line: Cpn1027 also co-precipitated GSK3β.We found that the C. pneumoniae-infected cells were more resistant to apoptosis induction and the anti-apoptotic activity was dependent on β-catenin.Thus, the current study suggests that the chlamydial inclusion protein Cpn1027 may be able to manipulate host Wnt signaling pathway for enhancing the chlamydial anti-apoptotic activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology & Immunology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States of America.

ABSTRACT
We previously identified hypothetical protein Cpn1027 as a novel inclusion membrane protein that is unique to Chlamydia pneumoniae. In the current study, using a yeast-two hybrid screen assay, we identified host cell cytoplasmic activation/proliferation-associated protein 2 (Caprin2) as an interacting partner of Cpn1027. The interaction was confirmed and mapped to the C-termini of both Cpn1027 and Caprin2 using co-immunoprecipitation and GST pull-down assays. A RFP-Caprin2 fusion protein was recruited to the chlamydial inclusion and so was the endogenous GSK3β, a critical component of the β-catenin destruction complex in the Wnt signaling pathway. Cpn1027 also co-precipitated GSK3β. Caprin2 is a key regulator of the Wnt signaling pathway by promoting the recruitment of the β-catenin destruction complex to the cytoplasmic membrane in the presence of Wnt signaling while GSK3β is required for priming β-catenin for degradation in the absence of Wnt signaling. The Cpn1027 interactions with Caprin2 and GSK3β may allow C. pneumoniae to actively sequester the β-catenin destruction complex so that β-catenin is maintained even in the absence of extracellular Wnt activation signals. The maintained β-catenin can trans-activate Wnt target genes including Bcl-2, which may contribute to the chlamydial antiapoptotic activity. We found that the C. pneumoniae-infected cells were more resistant to apoptosis induction and the anti-apoptotic activity was dependent on β-catenin. Thus, the current study suggests that the chlamydial inclusion protein Cpn1027 may be able to manipulate host Wnt signaling pathway for enhancing the chlamydial anti-apoptotic activity.

No MeSH data available.


Related in: MedlinePlus