Protein homeostasis maintains proper intracellular balance by promoting protein folding and clearance mechanisms while minimizing the stress caused by the accumulation of misfolded and damaged proteins. Chronic expression of aggregation-prone proteins is deleterious to the cell and has been linked to a wide range of conformational disorders. The molecular response to misfolded proteins is highly conserved and generally studied as a cell-autonomous process. Here, we provide evidence that neuronal signaling is an important modulator of protein homeostasis in post-synaptic muscle cells. In a forward genetic screen in Caenorhabditis elegans for enhancers of polyglutamine aggregation in muscle cells, we identified unc-30, a neuron-specific transcription factor that regulates the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). We used additional sensors of protein conformational states to show that defective GABA signaling or increased acetylcholine (ACh) signaling causes a general imbalance in protein homeostasis in post-synaptic muscle cells. Moreover, exposure to GABA antagonists or ACh agonists has a similar effect, which reveals that toxins that act at the neuromuscular junction are potent modifiers of protein conformational disorders. These results demonstrate the importance of intercellular communication in intracellular homeostasis.