PRRG4 and breast cancer: Interestingly, in addition to Ndfip proteins, the PRRG4 protein has also been implicated in the regulation of Robo1 receptors in vitro, and in the context of breast cancer tumor metastases, PRRG4 has been shown to regulate Robo1 degradation through recruitment of Nedd4 (Justice et al., 2017; Zhang et al., 2020).