SLC1A5 and breast cancer: However, its role in tumorigenesis remains controversial; several studies support the tumor-promoting function of RNF5 in different cancers by targeting multiple substrates [24, 37–39], while a tumor-inhibiting function in breast cancers has also been reported: RNF5 induces the ubiquitination and degradation of glutamine carrier proteins SLC1A5/38A2 to decrease glutamine uptake and suppress the tumorigenesis of breast cancers that carry mutated TP53 [40].