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CXCR7 protein expression in human adult brain and differentiated neurons.

Shimizu S, Brown M, Sengupta R, Penfold ME, Meucci O - PLoS ONE (2011)

Bottom Line: Furthermore, confocal microscopy and binding assays in cultured neurons show that CXCR7 protein is mainly located into cytoplasm, while little to no protein expression is found on neuronal plasma membrane.Interestingly, specific CXCR7 ligands that inhibit CXCL12 binding to CXCR7 do not alter CXCR4-activated survival signaling (pERK/pAkt) in rat cortical neurons.Overall, these results implicate CXCR4 as the main CXCL12 signaling receptor on the surface of differentiated neurons and suggest that CXCR7 may interact with CXCR4 at the intracellular level, possibly affecting CXCR4 trafficking and/or coupling to other proteins.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America.

ABSTRACT

Background: CXCR7 and CXCR4 are receptors for the chemokine CXCL12, which is involved in essential functions of the immune and nervous systems. Although CXCR7 transcripts are widely expressed throughout the central nervous system, little is known about its protein distribution and function in the adult brain. To evaluate its potential involvement in CXCL12/CXCR4 signaling in differentiated neurons, we studied CXCR7 protein expression in human brain and cultured neurons.

Methodology/principal findings: Immunohistochemistry and RT-PCR analyses of cortex and hippocampus from control and HIV-positive subjects provided the first evidence of CXCR7 protein expression in human adult neurons, under normal and pathological conditions. Furthermore, confocal microscopy and binding assays in cultured neurons show that CXCR7 protein is mainly located into cytoplasm, while little to no protein expression is found on neuronal plasma membrane. Interestingly, specific CXCR7 ligands that inhibit CXCL12 binding to CXCR7 do not alter CXCR4-activated survival signaling (pERK/pAkt) in rat cortical neurons. Neuronal CXCR7 co-localizes to some extent with the endoplasmic reticulum marker ERp29, but not with early/late endosome markers. Additionally, large areas of overlap are detected in the intracellular pattern of CXCR7 and CXCR4 expression.

Conclusions/significance: Overall, these results implicate CXCR4 as the main CXCL12 signaling receptor on the surface of differentiated neurons and suggest that CXCR7 may interact with CXCR4 at the intracellular level, possibly affecting CXCR4 trafficking and/or coupling to other proteins.

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CXCR7 partially co-localizes with endoplasmic reticulum marker                            ERp29.Human neurons were incubated with antibodies against CXCR7 (11G8, green)                            and ERp29 (red) as reported above and in the methods. Mouse IgG1 isotype                            control was used as negative control (NC). Overlapping staining of CXCR7                            and ERp29 (yellow) is detected in many neurons mostly in the perinuclear                            region. Image labeled as “Merged” is an enlargement of the                            CXCR7+ERp29 image shown in the inset plus the nuclear staining,                            whereas the image labeled as “lower plane” is the merge of                            CXCR7+ERp29 from a different plane of the same cell. Scale bar: 10                            µm.
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pone-0020680-g008: CXCR7 partially co-localizes with endoplasmic reticulum marker ERp29.Human neurons were incubated with antibodies against CXCR7 (11G8, green) and ERp29 (red) as reported above and in the methods. Mouse IgG1 isotype control was used as negative control (NC). Overlapping staining of CXCR7 and ERp29 (yellow) is detected in many neurons mostly in the perinuclear region. Image labeled as “Merged” is an enlargement of the CXCR7+ERp29 image shown in the inset plus the nuclear staining, whereas the image labeled as “lower plane” is the merge of CXCR7+ERp29 from a different plane of the same cell. Scale bar: 10 µm.

Mentions: The data presented show that CXCR7 is expressed in intracellular compartments in differentiated neurons, but the exact localization is still unclear. Previous studies in human T lymphocytes reported expression of CXCR7 in endosome vesicles, though this finding is still controversial [15]. However, CXCR7 does not co-localize with early (EEA1) or late (Rab7, Rab11) endosome markers in human neurons (Figure S2), suggesting that CXCR7 plays different roles in neurons and immune cells. Further analysis in neurons revealed a partial co-localization of CXCR7 with the endoplasmic reticulum (ER) marker ERp29 (Figure 8) [40]. The ER is part of the secretory pathway implicated in protein translocation to the cell surface, and it is commonly considered a default pathway. These data suggest that CXCR7 may be re-directed to the cell surface under specific cellular conditions or be implicated in trafficking of other proteins. Based on the CXCR7/CXCR4 expression pattern shown previously (Figures 4–5), this may include CXCR4-a hypothesis currently under investigation in our laboratory.


CXCR7 protein expression in human adult brain and differentiated neurons.

Shimizu S, Brown M, Sengupta R, Penfold ME, Meucci O - PLoS ONE (2011)

CXCR7 partially co-localizes with endoplasmic reticulum marker                            ERp29.Human neurons were incubated with antibodies against CXCR7 (11G8, green)                            and ERp29 (red) as reported above and in the methods. Mouse IgG1 isotype                            control was used as negative control (NC). Overlapping staining of CXCR7                            and ERp29 (yellow) is detected in many neurons mostly in the perinuclear                            region. Image labeled as “Merged” is an enlargement of the                            CXCR7+ERp29 image shown in the inset plus the nuclear staining,                            whereas the image labeled as “lower plane” is the merge of                            CXCR7+ERp29 from a different plane of the same cell. Scale bar: 10                            µm.
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Related In: Results  -  Collection

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pone-0020680-g008: CXCR7 partially co-localizes with endoplasmic reticulum marker ERp29.Human neurons were incubated with antibodies against CXCR7 (11G8, green) and ERp29 (red) as reported above and in the methods. Mouse IgG1 isotype control was used as negative control (NC). Overlapping staining of CXCR7 and ERp29 (yellow) is detected in many neurons mostly in the perinuclear region. Image labeled as “Merged” is an enlargement of the CXCR7+ERp29 image shown in the inset plus the nuclear staining, whereas the image labeled as “lower plane” is the merge of CXCR7+ERp29 from a different plane of the same cell. Scale bar: 10 µm.
Mentions: The data presented show that CXCR7 is expressed in intracellular compartments in differentiated neurons, but the exact localization is still unclear. Previous studies in human T lymphocytes reported expression of CXCR7 in endosome vesicles, though this finding is still controversial [15]. However, CXCR7 does not co-localize with early (EEA1) or late (Rab7, Rab11) endosome markers in human neurons (Figure S2), suggesting that CXCR7 plays different roles in neurons and immune cells. Further analysis in neurons revealed a partial co-localization of CXCR7 with the endoplasmic reticulum (ER) marker ERp29 (Figure 8) [40]. The ER is part of the secretory pathway implicated in protein translocation to the cell surface, and it is commonly considered a default pathway. These data suggest that CXCR7 may be re-directed to the cell surface under specific cellular conditions or be implicated in trafficking of other proteins. Based on the CXCR7/CXCR4 expression pattern shown previously (Figures 4–5), this may include CXCR4-a hypothesis currently under investigation in our laboratory.

Bottom Line: Furthermore, confocal microscopy and binding assays in cultured neurons show that CXCR7 protein is mainly located into cytoplasm, while little to no protein expression is found on neuronal plasma membrane.Interestingly, specific CXCR7 ligands that inhibit CXCL12 binding to CXCR7 do not alter CXCR4-activated survival signaling (pERK/pAkt) in rat cortical neurons.Overall, these results implicate CXCR4 as the main CXCL12 signaling receptor on the surface of differentiated neurons and suggest that CXCR7 may interact with CXCR4 at the intracellular level, possibly affecting CXCR4 trafficking and/or coupling to other proteins.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America.

ABSTRACT

Background: CXCR7 and CXCR4 are receptors for the chemokine CXCL12, which is involved in essential functions of the immune and nervous systems. Although CXCR7 transcripts are widely expressed throughout the central nervous system, little is known about its protein distribution and function in the adult brain. To evaluate its potential involvement in CXCL12/CXCR4 signaling in differentiated neurons, we studied CXCR7 protein expression in human brain and cultured neurons.

Methodology/principal findings: Immunohistochemistry and RT-PCR analyses of cortex and hippocampus from control and HIV-positive subjects provided the first evidence of CXCR7 protein expression in human adult neurons, under normal and pathological conditions. Furthermore, confocal microscopy and binding assays in cultured neurons show that CXCR7 protein is mainly located into cytoplasm, while little to no protein expression is found on neuronal plasma membrane. Interestingly, specific CXCR7 ligands that inhibit CXCL12 binding to CXCR7 do not alter CXCR4-activated survival signaling (pERK/pAkt) in rat cortical neurons. Neuronal CXCR7 co-localizes to some extent with the endoplasmic reticulum marker ERp29, but not with early/late endosome markers. Additionally, large areas of overlap are detected in the intracellular pattern of CXCR7 and CXCR4 expression.

Conclusions/significance: Overall, these results implicate CXCR4 as the main CXCL12 signaling receptor on the surface of differentiated neurons and suggest that CXCR7 may interact with CXCR4 at the intracellular level, possibly affecting CXCR4 trafficking and/or coupling to other proteins.

Show MeSH
Related in: MedlinePlus