Future cellular networks are expected to be heterogeneous with dense deployments of base transceiver stations and access points (wireless nodes). Energy consumption and interference management are two major issues in such networks. The goal of this work is to develop a framework for deciding if particular nodes should be powered off to reduce interference and save energy. This is envisioned to occur over slow time-scales, i.e., on the order of minutes. The active nodes should provide a target quality of service (QoS) to all mobile users. A network utility maximization problem is formulated, which takes as input the network topology and aggregate demand information, and optimizes over the set of active nodes and the assignment of demands to the nodes. Centralized and distributed algorithms are presented that search for a local optimum, and numerical results are presented to illustrate the performance.