To increase the functionality of synthetic genetic circuits for programming cell populations and coordinating behavior across a population, we developed and analyzed an artificial cell-to-cell communication system in mammalian cells using nitric oxide signaling elements by integrating nitric oxide synthesis with the c-fos promoter, whose transcription activity could be triggered by the nitric oxide pathway. In the system, engineered 'sender' cells synthesized the intercellular messenger nitric oxide, which diffused into the environment and activated the c-fos promoter, and subsequently, green fluorescence protein (GFP) reporter expression in nearby engineered 'receiver' cells. Next, the sender module was integrated into the receivers under positive-feedback regulation, resulting in population density-dependent GFP expression in a quorum-sensing pattern. This artificial cell-to-cell communication system in mammalian cells could serve as a versatile tool for regulated gene expression and as building blocks for complex artificial gene regulatory networks for applications in gene therapy, tissue engineering, and biotechnology.