Lactate receptor GPR81 drives breast cancer growth and invasiveness through regulation of ECM properties and Notch ligand DLL4

The lactate receptor GPR81 contributes to cancer development, yet the mechanisms remain unclear. Here, we show that GPR81 is upregulated in human cancers and further upregulated by extracellular lactate and three-dimensional growth of breast cancer spheroids. GPR81 knockdown (KD) increased spheroid necrosis and reduced invasion and in vivo tumor growth. GPR81 KD altered GO terms relating to extracellular matrix (ECM) and cell adhesion, including upregulation of Protocadherin-7 (PCDH7), which exhibited a striking, clustered expression in spheroids. Single cell analysis revealed that PCDH7 was inversely related with Ki-67 and co-clustered with other GPR81 KD-upregulated genes including Ephrin-type-A receptor-7 (EPHA7). The matricellular protein SPARC and the Notch ligand Delta-like-4 (DLL4), were downregulated upon GPR81 KD, and their KD elicited spheroid necrosis (DLL4) and inhibited invasion. We conclude that GPR81 supports breast cancer aggressiveness at least in part via SPARC and DLL4. Our findings substantiate GPR81 as a promising target in breast cancer treatment. MCF-7 cells stably expressing the empty pLKO.1 vector or GPR81 shRNA in pLKO.1, respectively, were grown in DMEM with either 5 mM glucose or 20 mM lactate for 72 h before being subjected to RNA sequencing (BGI).