We report an experimental demonstration of a functional cell for quantum-dot cellular automata (QCA), a transistorless approach to implement logic functions. The four-dot QCA cell is defined by a pair of series-connected, capacitively coupled input and output double dots. We demonstrate that, at low temperature, an electron switch in the input double dot induces an opposite electron switch in the output double dot, resulting in a complete polarization change of the QCA cell. Switching is verified by electrometer signals which are coupled to the output double dot. Experimental results suggest that electron motion in the coupled double dots is strongly correlated and can support high operating frequencies. Agreement between theoretical predictions and experimentally measured values of the dot potentials is excellent.