Folliculin interacts with p0071 (plakophilin-4) and deficiency is associated with disordered RhoA signalling, epithelial polarization and cytokinesis

Abstract

Inherited mutations in the folliculin (FLCN) gene cause the Birt-Hogg-Dubé syndrome of familial hair follicle tumours (fibrofolliculomas), lung cysts and kidney tumours. Though folliculin has features of a tumour suppressor, the precise function of the FLCN gene product is not well characterized. We identified plakophilin-4 (p0071) as a potential novel folliculin interacting protein by yeast two-hybrid analysis. We confirmed the interaction of folliculin with p0071 by co-immunoprecipitation studies and, in view of previous studies linking p0071 to the regulation of rho-signalling, cytokinesis and intercellular junction formation, we investigated the effect of cell folliculin status on p0071-related functions. Folliculin and p0071 partially co-localized at cell junctions and in mitotic cells, at the midbody during cytokinesis. Previously, p0071 has been reported to regulate RhoA signalling during cytokinesis and we found that folliculin deficiency was associated with increased expression and activity of RhoA and evidence of disordered cytokinesis. Treatment of folliculin-deficient cells with a downstream inhibitor of RhoA signalling (the ROCK inhibitor Y-27632) reversed the increased cell migration phenotype observed in folliculin-deficient cells. Deficiency of folliculin and of p0071 resulted in tight junction defects and mislocalization of E-cadherin in mouse inner medullary collecting duct-3 renal tubular cells. These findings suggest that aspects of folliculin tumour suppressor function are linked to interaction with p0071 and the regulation of RhoA signalling.

FLCN, a novel autophagy component, interacts with GABARAP and is regulated by ULK1 phosphorylation

“…For instance, FLCN also interacts with plakophilin-4 involved in desmosomal and adherens junctions. 54,55 Additionally, multiple pathways that drive cancer progression can become dysregulated when FLCN expression is lost, including defects in TGFB1 (transforming growth factor, β 1)-mediated signaling, 56,57 enhanced HIF1A (hypoxia inducible factor 1, α subunit [basic helix-loop-helix transcription factor]) activity 58 and TFE3 (transcription factor binding to IGHM enhancer 3) activity. 59 Therefore, FLCN appears to play a broader 'housekeeping' role in the cell and is likely to be a fundamental player in autophagy and cellular homeostasis outside the disease setting.…”

Molecular genetics and clinical features of Birt–Hogg–Dubé syndrome

“…FLCN loss resulted in increased cell-cell adhesion, disruption of cell polarity and dysregulated Rho A signaling. 85,86 Increased cell-cell adhesions were reported in FLCN -deficient lung cell lines in vitro 87 and marked reduction in E-cadherin expression at adherens junctions and increased alveolar apoptosis were observed in lungs of mice with lung-targeted Flcn inactivation. 88 These findings support a role for FLCN in maintaining critical cell-cell adhesions for maintenance of lung and kidney epithelial cell integrity ( Figure 7 ).…”

Folliculin-interacting proteins Fnip1 and Fnip2 play critical roles in kidney tumor suppression in cooperation with Flcn

“…Crystallographic studies have shown that the C terminus of FLCN may be distantly related to Differentially Expressed in Normal Cells and Neoplasia (DENN) domain proteins and may possess guanine nucleotide exchange factor activity toward RAB35 (16). FLCN modulates TFE3 localization (17), which may play an important role in the exit of stem cells from pluripotency (18), and interacts with other signaling pathways including the von Hippel-Lindau-hypoxia inducible factor-vascular endothelial growth factor axis (19)(20)(21), the TGF-beta pathway (22,23), Rho A signaling (24,25), cell cycle regulation (26,27), Rag-mediated amino acid sensing (28,29), and autophagy (30,31). These findings underscore FLCN as an important molecule, inactivation of which affects multiple pathways.…”