MEPB is a modulator of the activation function-2 (AF-2) of the androgen receptor (AR), increasing AR co-repressor binding. MEPB specifically binds the BF3 pocket of the androgen receptor where it modulates binding of co-regulators to the AF2 domain. MEPB was found to rescue degeneration in a mouse model of spinal bulbar muscular atrophy, a motor neuron disease caused by toxic gain of function of the androgen receptor.