CXCL12 receptor preference, signal transduction, biological response and the expression of 5T4 oncofoetal glycoprotein

Abstract

SummaryCXCL12 is a pleiotropic chemokine capable of eliciting multiple signal transduction cascades and functions, via interaction with either CXCR4 or CXCR7. Factors that determine CXCL12 receptor preference, intracellular signalling route and biological response are poorly understood but are of central importance in the context of therapeutic intervention of the CXCL12 axis in multiple disease states. We have recently demonstrated that 5T4 oncofoetal glycoprotein facilitates functional CXCR4 expression leading to CXCL12 mediated chemotaxis in mouse embryonic cells. Using wild type (WT) and 5T4 knockout (5T4KO) murine embryonic fibroblasts (MEFs), we now show that CXCL12 binding to CXCR4 activates both the ERK and AKT pathways within minutes, but while these pathways are intact, they are non-functional in 5T4KO cells treated with CXCL12. Importantly, in the absence of 5T4 expression, CXCR7 is upregulated and becomes the predominant receptor for CXCL12, activating a distinct signal transduction pathway with slower kinetics involving transactivation of the epidermal growth factor receptor (EGFR), eliciting proliferation rather than chemotaxis. Thus the surface expression of 5T4 marks the use of the CXCR4 rather than the CXCR7 receptor, with distinct consequences for CXCL12 exposure, relevant to the spread and growth of a tumour. Consistent with this hypothesis, we have identified human small cell lung carcinoma cells with similar 5T4/CXCR7 reciprocity that is predictive of biological response to CXCL12 and determined that 5T4 expression is required for functional chemotaxis in these cells.

SDF-1 Chemokine Signalling Modulates the Apoptotic Responses to Iron Deprivation of Clathrin-Depleted DT40 Cells

“…As Akt and ERK are pivotal to the CXCR4 signalling pathway, and since CXCR4 only binds SDF-1 [53], the constitutive stimulation of these enzymes in DKO-R cells is consistent with an autocrine effect of endogenously synthesised SDF-1. In agreement with our observations, a dramatic increase in Akt and ERK1/2 phosphorylation in response to SDF-1 stimulation has been noted in MEF cells and this activation was inhibited by the CXCR4 inhibitor AMD3100 but not by a CXCR7 inhibitor [54].…”

Targeting the 5T4 oncofetal glycoprotein with an antibody drug conjugate (A1mcMMAF) improves survival in patient-derived xenograft models of acute lymphoblastic leukemia

“…Most mature cells, including lymphoid cells, do not express it. 5T4 is associated with differentiating embryonic stem cells, 12,13 and mechanistically associated with the directional movement of cells through the regulation of epithelial mesenchymal transition, 12–14 facilitation of CXCL12/CXCR4 chemotaxis 15,16 and favoring non-canonical over canonical WNT/β–catenin pathway signaling. 17,18 5T4 is expressed by tumor-initiating cells in human non-small cell carcinomas 19 and by a number of carcinomas.…”

Understanding and exploiting 5T4 oncofoetal glycoprotein expression

“…Further, in the absence of 5T4 expression, CXCR7 is upregulated and becomes the predominant receptor for CXCL12, activating a distinct signal transduction pathway with slower kinetics [21,34,38] show CXCL12 directional migration of H1048 (5T4 positive) but not 5T4KD H1048 or 5T4 negative DMS114 human small cell carcinoma cells. No gradient (NG); *p < 0.05.…”

“…No gradient (NG); *p < 0.05. (b) Survival analysis [34] shows only 5T4 negative DMS114 but not 5T4 positive H1048 have enhanced survival in CXCL12 mediated through the CXCR7 receptor (blocking with specific inhibitor CCX733). (c) In 5T4 positive cells some 5T4 and CXCR4 co-localize at the plasma membrane, this facilitates the response to a CXCL12 gradient leading to activation of the ERK/AKT signalling pathways within minutes which subsequently results in directional movement (chemotaxis).…”

“…Thus the surface expression of 5T4 marks the use of the CXCR4 rather than the CXCR7 receptor, with distinct consequences for CXCL12 exposure relevant to the spread and growth of a tumour [34]. It is possible that 5T4 plays a role in breaking the natural CXCR7 receptor bias of the chemokine CXCL12 (tenfold higher affinity) and provides for a switch in homeostatic function induced by the chemokine.…”