Ras promotes macropinocytic nutrient uptake by suppressing the albumin recycling receptor FcRn.

Macropinocytosis and lysosomal degradation of extracellular protein constitute a nutrient acquisition pathway in Ras-driven cancers. By catabolizing albumin, the most abundant plasma protein, Ras-transformed cells sustain growth in environments where free amino acids are scarce. Under physiological conditions, however, albumin is normally protected from lysosomal degradation by the neonatal Fc receptor (FcRn), which recycles albumin back to the extracellular space. Here, by investigating how cancer cells overcome FcRn-mediated albumin recycling, we identify the Ras-Erk MAPK signaling pathway as a critical regulator of FcRn. Expression of constitutively active Ras variants or stimulation with growth factors represses FcRn transcription through activation of the MAPK pathway, leading to decreased FcRn protein abundance. Conversely, pharmacological inhibition of Ras-MAPK signaling de-represses FcRn expression. Restoring FcRn levels in Ras-transformed cells limits lysosomal albumin degradation and impairs the proliferation of cells that depend on albumin as an essential amino acid source. Thus, oncogenic Ras signaling promotes the nutritional utilization of albumin by suppressing FcRn, thereby supporting cancer cell adaptation to nutrient-poor environments.