Macrophages may promote cancer growth via a GM-CSF/HB-EGF paracrine loop that is enhanced by CXCL12.
BACKGROUND
Increased numbers of tumour-associated macrophages correlate with shortened survival in some cancers. The molecular bases of this correlation are not thoroughly understood. Events triggered by CXCL12 may play a part, as CXCL12 drives the migration of both CXCR4-positive cancer cells and macrophages and may promote a molecular crosstalk between them.


RESULTS
Samples of HER1-positive colon cancer metastases in liver, a tissue with high expression of CXCL12, were analysed by immunohistochemistry. In all of the patient biopsies, CD68-positive tumour-associated macrophages presented a mixed CXCL10 (M1)/CD163 (M2) pattern, expressed CXCR4, GM-CSF and HB-EGF, and some stained positive for CXCL12. Cancer cells stained positive for CXCR4, CXCL12, HER1, HER4 and GM-CSF. Regulatory interactions among these proteins were validated via experiments in vitro involving crosstalk between human mononuclear phagocytes and the cell lines DLD-1 (human colon adenocarcinoma) and HeLa (human cervical carcinoma), which express the above-mentioned ligand/receptor repertoire. CXCL12 induced mononuclear phagocytes to release HB-EGF, which activated HER1 and triggered anti-apoptotic and proliferative signals in cancer cells. The cancer cells then proliferated and released GM-CSF, which in turn activated mononuclear phagocytes and induced them to release more HB-EGF. Blockade of GM-CSF with neutralising antibodies or siRNA suppressed this loop.


CONCLUSIONS
CXCL12-driven stimulation of cancer cells and macrophages may elicit and reinforce a GM-CSF/HB-EGF paracrine loop, whereby macrophages contribute to cancer survival and expansion. The involvement of mixed M1/M2 GM-CSF-stimulated macrophages in a tumour-promoting loop may challenge the paradigm of tumour-favouring macrophages as polarized M2 mononuclear phagocytes.
Department of Medicine, Section of Hematology, University of Verona, Verona, Italy.
Antonella
A
Rigo
Michele
M
Gottardi
Alberto
A
Zamò
Pierluigi
P
Mauri
Massimiliano
M
Bonifacio
Mauro
M
Krampera
Ernesto
E
Damiani
Giovanni
G
Pizzolo
Fabrizio
F
Vinante
D000368:Aged; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015152:Blotting, Northern; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D054377:Chemokine CXCL12 / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000378:metabolism; D005434:Flow Cytometry; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism* / Q000494:pharmacology; D006367:HeLa Cells; D066257:Heparin-binding EGF-like Growth Factor; D006801:Humans; D007120:Immunochemistry; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism* / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism*; D013058:Mass Spectrometry; D051379:Mice; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction
D054377:Chemokine CXCL12; C587883:HBEGF protein, human; C587884:Hbegf protein, mouse; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D066246:ErbB Receptors