FLCN-Rab35 Signaling Pathway Feedback Regulates EGF-induced EGFR Degradation

Epidermal growth factor receptor(EGFR)plays an essential role during tumorigenesis.The overexpression of EGFR increases tumor proliferation,growth,survival and migration by activating the PI3K-AKT and ERK-RSK pathways.To avoid constitutive signaling and tumor progression,signal termination usually occurs immediately after EGFR activation and physiological function by multiple feedback loops.In fact,EGF binding not only activates EGFR and its downstream signaling pathway,but also feedback downregulates expression of the EGFR at cell surface,which is achieved by endocytosis and degradation of the activated receptor and associated signaling proteins.Folliculin(FLCN),a tumor suppressor disrupted in various malignancies,contains a divergent DENN module that retains the basic role as guanine nucleotide exchange factors(GEFs)for Rab GTPases.However,it is unknown whether FLCN contributes degradation of the EGFR.In this study,we investigated the potential tumor suppressor molecular mechanism of FLCN as a GEF for Rab35 in a EGF-induced EGFR degradation model in Hela cells.Here,we demonstrate that the FLCN DENN domain binds Rab35 and functions as a GEF in vivo.Interfering with either FLCN or Rab35 reduces the rate of EGFR degradation,resulting in prolonged signaling and increased activation of AKT and ERK.Furthermore,our data shows that FLCN promotes the EGF-induced degradation of EGFR mediated by Rab35.Of special interest is the observation that erlotinib,one of the selective EGFR-tyrosine kinase inhibitors,not only obstructs the receptor-mediated cellular signaling,but abolishes EGF-stimulated EGFR degradation.Importantly,the further experimental results reveal that EGF facilitates the activation of Rab35,and FLCN modulates EGF-dependent Rab35 activation and cell proliferation.