Effects of the chemokine CXCL12 and combined internalization of its receptors CXCR4 and CXCR7 in human MCF-7 breast cancer cells.
The chemokine CXCL12 (stromal cell-derived factor-1, SDF-1) and its receptor CXCR4 play a major role in tumor initiation, promotion, progression and metastasis, especially for breast cancer cells. Recently, CXCR7 has been identified as a second receptor for CXCL12; nevertheless, it also binds CXCL11 (interferon-inducible T cell α chemoattractant, I-TAC). However, little is known about the co-expression of the two receptors and their interactions. Quantitative reverse transcription plus the polymerase chain reaction has demonstrated that both receptors are frequently co-expressed in breast cancer cell lines, whereas other tumor cell lines often express only one of them. For interaction studies, we chose MCF-7 breast cancer cells, since they highly express CXCR4 and CXCR7 at the protein level but not CXCR3 (another target for CXCL11). Immunofluorescence and gold-labeling by light and electron microscopy, respectively, revealed that both receptors were localized at the cell surface in non-stimulated cells. After exposure to CXCL12 or CXCL11, the receptors were rapidly internalized alone or in close proximity. Stimulation with the CXCR4- or CXCR7-selective non-peptide antagonists AMD3100 and CCX733 resulted not only in single internalization but partly also in co-internalization of the two receptors. Furthermore, both chemokine ligands reduced staurosporine-induced apoptosis and caspase-3/7 activation; however, the selective inhibitors merely had partial inhibitory effects on these biological responses. Our findings suggest that CXCR4 and CXCR7 closely interact in breast cancer cells. Both are co-internalized, transduce signals and induce further biological effects partly independently of a selective stimulus or antagonist.
Department of Anatomy, University of Kiel, Olshausenstraße 40, 24098, Kiel, Germany.
Kirsten
K
Hattermann
Eric
E
Holzenburg
Friederike
F
Hans
Ralph
R
Lucius
Janka
J
Held-Feindt
Rolf
R
Mentlein
D017209:Apoptosis / Q000502:physiology; D001596:Benzylamines; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D054377:Chemokine CXCL12 / Q000494:pharmacology*; D000080027:Cyclams; D005260:Female; D006571:Heterocyclic Compounds / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D061986:MCF-7 Cells; D054387:Receptors, CXCR / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D019718:Receptors, CXCR4 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism*; D015398:Signal Transduction; D013268:Stimulation, Chemical
C501896:ACKR3 protein, human; D001596:Benzylamines; C515255:CXCL12 protein, human; C527276:CXCR4 protein, human; D054377:Chemokine CXCL12; D000080027:Cyclams; D006571:Heterocyclic Compounds; D008024:Ligands; D054387:Receptors, CXCR; D019718:Receptors, CXCR4; C088327:plerixafor