Negative regulation of EGFR signalling by the human folliculin tumour suppressor protein

Abstract

Germline mutations in the Folliculin (FLCN) tumour suppressor gene result in fibrofolliculomas, lung cysts and renal cancers, but the precise mechanisms of tumour suppression by FLCN remain elusive. Here we identify Rab7A, a small GTPase important for endocytic trafficking, as a novel FLCN interacting protein and demonstrate that FLCN acts as a Rab7A GTPase-activating protein. FLCN−/− cells display slower trafficking of epidermal growth factor receptors (EGFR) from early to late endosomes and enhanced activation of EGFR signalling upon ligand stimulation. Reintroduction of wild-type FLCN, but not tumour-associated FLCN mutants, suppresses EGFR signalling in a Rab7A-dependent manner. EGFR signalling is elevated in FLCN−/− tumours and the EGFR inhibitor afatinib suppresses the growth of human FLCN−/− cells as tumour xenografts. The functional interaction between FLCN and Rab7A appears conserved across species. Our work highlights a mechanism explaining, at least in part, the tumour suppressor function of FLCN.

FLCN is a novel Rab11A-interacting protein that is involved in the Rab11A-mediated recycling transport

“…This led to the hypothesis that FLCN binds Rab GTPases and regulates vesicular trafficking processes (Nookala et al, 2012). In support of this view, three recent reports have shown that FLCN interacts through its DENN domain with Rab34, Rab7A and Rab35 (Starling et al, 2016;Laviolette et al, 2017;Zheng et al, 2017). In one study, Dodding's group discovered that the FLCN-Rab34 interaction regulates the intracellular movement of lysosomes in a nutrient-sensitive manner in HeLa cells (Starling et al, 2016).…”

“…recently been found to interact with Rab7A in several human tumor cell lines (Laviolette et al, 2017), we considered the FLCN-Rab7A interaction as a positive control in our co-IP experiments. It is probably worth noting that, on the basis of these co-IP data; it seems that only a small proportion of GFP-tagged Rab proteins coimmunoprecipitated with FLCN.…”

“…However, it is only recently that the evidence of FLCN in protein transport has started to emerge, probably because the cargos transported by FLCN were largely unknown. During the ongoing of this research, two groups reported that FLCN promotes the transport of EGFR to the lysosome for degradation by modulating the activities of Rab7 (Laviolette et al, 2017) and Rab35 (Zheng et al, 2017), respectively.…”

Hereditary kidney cancer syndromes: Genetic disorders driven by alterations in metabolism and epigenome regulation

“…Disruption of FLCN‐FNIPs interaction drives upregulated mTORC1‐dependent protein synthesis, upregulated PGC1 α ‐ dependent mitochondrial oxidative metabolism and aberrant kidney cell proliferation . Crystallography of FLCN protein exhibited that FLCN has a DENN domain in its C‐terminus, suggesting FLCN may act as a modifier for Rab small GTPase family as well as a regulator for membranous trafficking . In addition, FLCN shows either GAP activity towards RagC/D GTPases or GEF activity towards RagA/B GTPases, which consequently regulates mTORC1 localization on lysosomes, implying that FLCN may regulate multiple small GTPases .…”

“…[20][21][22][23][24] Crystallography of FLCN protein exhibited that FLCN has a DENN domain in its C-terminus, suggesting FLCN may act as a modifier for Rab small GTPase family as well as a regulator for membranous trafficking. 25,26 In addition, FLCN shows either GAP activity towards RagC/D GTPases or GEF activity towards RagA/B GTPases, which consequently regulates mTORC1 localization on lysosomes, implying that FLCN may regulate multiple small GTPases. 27,28 These findings highlight that FLCN plays important roles in metabolism, and disruption of metabolism under FLCN deficiency may drive aberrant kidney cell proliferation.…”