An uplink-downlink cellular network is studied in which the first base station with $M_1$ antennas receives independent messages from its $N_1$ serving users and the second base station with $M_2$ antennas, on the other hand, transmits independent messages to its $N_2$ serving users. Each user is assumed to have a single antenna. Under this uplink--downlink setting, the sum dof is completely characterized. The achievability follows uplink inter-cell interference alignment and downlink inter-cell and intra-cell interference nulling using multiple antennas.