# The autophagy inhibitor NSC185058 suppresses mTORC1-mediated protein anabolism in cultured skeletal muscle

## TL;DR

A drug called NSC185058, which blocks autophagy, also reduces protein production in muscle cells by inhibiting a key signaling complex called mTORC1.

## Contribution

This study is the first to show that autophagy inhibition directly suppresses mTORC1 activity, revealing a bidirectional regulatory relationship.

## Key findings

- Inhibiting autophagy with NSC185058 suppresses mTORC1 activity in cultured skeletal muscle.
- mTORC1 cannot function when autophagy is inhibited by NSC185058.
- Autophagy serves as an input for mTORC1 signaling, and mTORC1 inhibition of autophagy acts as homeostatic feedback.

## Abstract

The mammalian target of rapamycin (mTOR), and specifically the mTOR complex 1 (mTORC1) is the central regulator of anabolism in skeletal muscle. Among the many functions of this kinase complex is the inhibition of the catabolic process of autophagy; however, less work has been done in investigating the role of autophagy in regulating mTORC1 signaling. Using an in vitro model to better understand the pathways involved, we activated mTORC1 by several different means (growth factors, leucine supplementation, or muscle contraction), alone or with the autophagy inhibitor NSC185058. We found that inhibiting autophagy with NSC185058 suppresses mTORC1 activity, preventing any increase in cellular protein anabolism. These decrements were the direct result of action on the mTORC1 kinase, which we demonstrate, for the first time, cannot function when autophagy is inhibited by NSC185058. Our results indicate that, far from being a matter of unidirectional action, the relationship between mTORC1 and the autophagic cascade is more nuanced, with autophagy serving as an mTORC1 input, and mTORC1 inhibition of autophagy as a form of homeostatic feedback to regulate anabolic signaling. Future studies of cellular metabolism will have to consider this fundamental intertwining of protein anabolism and catabolism, and how it ultimately serves to regulate muscle proteostasis.