Extracellular ATP activates multiple signalling pathways and potentiates growth factor-induced c-fos gene expression in MCF-7 breast cancer cells

In the human breast cancer cell line MCF-7, the nucleotides ATP gammaS and UTP, acting extracellularly through the purinergic receptor P2Y(2), lead to elevated intracellular calcium levels and increased proliferation. ATP gammaS and UTP treatment of MCF-7 cells activated transcription of the immediate early gene c-fos, an important component in the response to proliferative stimulation. c-fos induction was enhanced by co-treatment with ATP gammaS and a variety of proliferative agents including growth factors, tumour promoters and stress. Stimulation with ATP gammaS or epidermal growth factor (EGF) led to extracellular signal-regulated kinase (ERK) activation and phosphorylation of the transcription factors CREB and Elk-1. Co-stimulation synergistically activated fos expression and notably led to increased levels of ERK, CREB and EGF receptor phosphorylation, as well as hyperphosphorylation of ternary complex factor. Nevertheless, the ERK pathway does not fully account for this synergy since fos induction was differentially sensitive to the MEK inhibitor U0126, indicating that these two agonists signal differently to this immediate early gene. Thus, extracellular nucleotides cooperate with growth factors to activate genes linked to the proliferative response in MCF-7 cells through activation of specific purinergic receptors, which thereby represent important potential targets for arresting the neoplastic progression of breast cancer cells.