Interaction Between CCL18 and GPR30 Differs from the Interaction Between Estradiol and GPR30

Background/Aim: C-C motif chemokine ligand 18 (CCL18) is overexpressed in the microenvironment of tumors, promotes invasion and metastasis and is thus important for the therapeutic outcome of many tumor entities. The Gs-coupled seven-transmembrane receptor GPR30 is known as both a CCL18 and an estrogen receptor; its activation by estradiol leads to a transactivation of membrane-tethered pro-heparin-binding EGF-like growth factor and the MAPK/ERK pathway. We examined whether this signaling pathway remains the same under CCL18 stimulation, as opposed to estradiol stimulation. Materials and Methods: We investigated the effects of CCL18 on the lung cancer cell line A549, that show low GPR30 expression and the breast cancer cell lines MCF-7, that has high GPR30 expression and MDA-MB-231. These cells were stimulated in different media with CCL18 and then analyzed by qPCR, In-Cell Western®, western blot and ELISA. Results: Many similarities on the effect of CCL18 on the already known estradiol-activated signaling pathway via the G protein-coupled estrogen receptor GPR30 were identified. GPR30 is involved in the expression of matrix metalloproteinases (MMPs), which may play a role in the transactivation of ERK-1/-2 via the cleavage of membrane-bound HB-EGF, via Src-related tyrosine kinases and Gβγ-subunits. With increasing CCL18 concentration, the expression of MMP7 decreased in A549 cells. With decreasing estrogen content of the medium, there was an increasing effect of CCL18 on the inhibition of the relative expression of MMP7. Inhibition of GPR30 with G15 also resulted in a decrease in the relative expression of MMP7, irrespective of the subsequent stimulation with CCL18. This is a rather unexpected result, because the estrogen estradiol and CCL18 both activate GPR30. MCF-7 cells which express more GPR30 did not show any dependence of the relative MMP7 expression on CCL18 except in estrogen-free FCS medium. CCL18 induced an increased relative ERK activation in In-Cell western (ICW) at A549 cells. Stimulation with CCL18 caused decreased ERK activation with simultaneous inhibition of adenylate cyclase in MCF-7. However, stimulation with CCL18 and simultaneous inhibition of cyclooxygenase in MCF-7 resulted in increased ERK activation. In A549, stimulation with CCL18 and co-incubation with dbcAMP resulted in decreased ERK activation in both ICW and Western blot. Conclusion: In summary, the Gs-coupled receptor GPR30 plays an important role in the signaling pathway of CCL18. CCL18 and estradiol may not lead to the same signaling pathway after activating GPR30.