Monomeric and dimeric CXCL12 inhibit metastasis through distinct CXCR4 interactions and signaling pathways

Abstract

Chemokines and chemokine receptors are extensively and broadly involved in cancer metastasis. Previously, we demonstrated that epigenetic silencing of the chemokine CXCL12 sensitizes breast and colon cancer cells to endocrine signaling and metastasis to distant tissues. Yet, the precise mechanism whereby CXCL12 production by tumor cells regulates dissemination remains unclear. Here, we show that administration of CXCL12 extended survival of tumorbearing mice by potently limiting metastasis of colorectal carcinoma or murine melanoma. Because secreted CXCL12 is a mixture of monomeric and dimeric species in equilibrium, oligomeric variants that either promote (monomer) or halt (dimer) chemotaxis were used to dissect the mechanisms interrupting carcinoma metastasis. Monomeric CXCL12 mobilized intracellular calcium, inhibited cAMP signaling, recruited β-arrestin-2, and stimulated filamentous-actin accumulation and cell migration. Dimeric CXCL12 activated G-protein-dependent calcium flux, adenylyl cyclase inhibition, and the rapid activation of ERK1/2, but only weakly, if at all, recruited arrestin, stimulated actin polymerization, or promoted chemotaxis. NMR analyses illustrated that CXCL12 monomers made specific contacts with CXCR4 that were lost following dimerization. Our results establish the potential for inhibiting CXCR4-mediated metastasis by administration of CXCL12. Chemokine-mediated migration and β-arrestin responses did not dictate the antitumor effect of CXCL12. We conclude that cellular migration is tightly regulated by selective CXCR4 signaling evoked by unique interactions with distinct ligand quaternary structures.malignancy | functional selectivity | cellular idling | cancer therapeutics | chemokine oligomer C hemokines are chemoattractant cytokines that bind G-protein-coupled receptors and are mediators for many physiological processes including cell trafficking, angiogenesis, and embryogenesis (1-3). Chemokine receptor signaling is linked with cancer metastasis as well as infiltration of tumor-associated immune cells, neoangiogenesis, and proliferation (4, 5). Chemokines as primary mediators of metastasis were first identified by Muller and colleagues who implicated the chemokine receptor CXCR4 in tumor cell trafficking (6-8). At least 23 different cancers have been shown to express elevated levels of CXCR4, sensitizing these cancers to CXCL12 gradients in distant tissues (9). CXCL12 is constitutively expressed in the bone marrow, lungs, and liver, which are common tissues of metastatic growth. Efforts to block metastatic dissemination have mainly used small molecule antagonists of CXCR4 (10) to limit cancer malignancy (11, 12). However, this avenue has proven difficult to move into the clinic (5, 12), suggesting alternative strategies to interfere with CXCR4-guided metastatic homing (for example, by the use of agonists rather than antagonists) are required. Our previous data indicate that epigenetic silencing of the Cxcl12 promoter enhances metastasis of colonic and mammary carcinoma, implicating...

CXCL11-dependent induction of FOXP3-negative regulatory T cells suppresses autoimmune encephalomyelitis

“…Previous studies demonstrated that a unique feature of GPCRs is their capability to induce a variety of signaling cascades via activation of the same receptor (17,18,20,21,48). These findings are in accordance with the previous observation that CXCL12-induced cell migration, via CXCR4, is independent of its ability to induce cytokine production via the same receptor (49).…”

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