SLC38A9: A lysosomal amino acid transporter at the core of the amino acid-sensing machinery that controls MTORC1.

The mechanistic target of rapamycin (serine/threonine kinase) complex 1 (MTORC1) acts as a crucial regulator of cellular metabolism by integrating growth factor presence, energy and nutrient availability to coordinate anabolic and catabolic processes, and controls cell growth and proliferation. Amino acids are critical for MTORC1 activation, but the molecular mechanisms involved in sensing their presence are just beginning to be understood. We recently reported that the previously uncharacterized amino acid transporter SLC38A9 is a member of the lysosomal sensing machinery that signals amino acid availability to MTORC1. SLC38A9 is the first component of this complex shown to physically engage amino acids, suggesting a role at the core of the amino acid-sensing mechanism.