p directly regulates q iff p is immediately causally upstream of q and p regulates q.

Process(P1) directly regulates process(P2) iff: P1 regulates P2 via direct physical interaction between an agent executing P1 (or some part of P1) and an agent executing P2 (or some part of P2). For example, if protein A has protein binding activity(P1) that targets protein B and this binding regulates the kinase activity (P2) of protein B then P1 directly regulates P2.