Flightless-I Blocks p62-Mediated Recognition of LC3 to Impede Selective Autophagy and Promote Breast Cancer Progression

Abstract

p62 is a receptor that facilitates selective autophagy by interacting simultaneously with cargoes and LC3 protein on the autophagosome to maintain cellular homeostasis. However, the regulatory mechanism(s) behind this process and its association with breast cancer remain to be elucidated. Here, we report that Flightless-I (FliI), a novel p62-interacting protein, promotes breast cancer progression by impeding selective autophagy. FliI was highly expressed in clinical breast cancer samples, and heterozygous deletion of FliI retarded the development of mammary tumors in PyVT mice. FliI induced p62-recruited cargoes into Triton X-100 insoluble fractions (TI) to form aggregates, thereby blocking p62 recognition of LC3 and hindering p62-dependent selective autophagy. This function of Flil was reinforced by Akt-mediated phosphorylation at Ser436 and inhibited by phosphorylation of Ulk1 at Ser64. Obstruction of autophagic clearance of p62-recruited cargoes by FliI was associated with the accumulation of oxidative damage on proteins and DNA, which could contribute to the development of cancer. Heterozygous knockout of FliI facilitated selectively autophagic clearance of aggregates, abatement of ROS levels, and protein oxidative damage, ultimately retarding mammary cancer progression. In clinical breast cancer samples, Akt-mediated phosphorylation of FliI at Ser436 negatively correlated with long-term prognosis, while Ulk1-induced FliI phosphorylation at Ser64 positively correlated with clinical outcome. Together, this work demonstrates that FliI functions as a checkpoint protein for selective autophagy in the crosstalk between FliI and p62-recruited cargoes, and its phosphorylation may serve as a prognostic marker for breast cancer. Flightless-I functions as a checkpoint protein for selective autophagy by interacting with p62 to block its recognition of LC3, leading to tumorigenesis in breast cancer..

Flightless I exacerbation of inflammatory responses contributes to increased colonic damage in a mouse model of dextran sulphate sodium-induced ulcerative colitis

“…Reduced levels of Flii expression, both genetically and using Flii neutralising antibodies, improves skin repair and regeneration in both small and large animal models of healing 7,8,10–12 . Studies have identified Flii as a repressor of estrogen receptor signalling and apoptosis suggesting roles in promotion of both skin cancer and breast cancer progression 13–15 . In contrast, Flii positively influences tissue regeneration in the context of Wnt signalling pathways during hair follicle regeneration and claw and digit tip regeneration 16,17 illustrating the diverse roles of this cytoskeletal protein.…”

The Activities of the Gelsolin Homology Domains of Flightless-I in Actin Dynamics

“…In agreement with our observations, previous investigations found that the GH1 truncated human Fli-I, GH26 did not influence the level of steady-state pyrenyl fluorescence suggesting the critical importance of GH1 in actin interaction ( Arora et al, 2015 ). Also, the human Fli-I protein carrying the E586K mutation in the GH1 domain failed to coimmunoprecipitate with actin in 293T cells ( He et al, 2018 ). Based on these considerations the GH1 domain of Fli-I is likely to be the main actin-binding site of the protein.…”

Mechanical Force and Actin Dynamics during Cutaneous Squamous Cell Carcinoma (cSCC) Progression: Opportunities for Novel Treatment Modalities

“…Studies have shown that downregulation of gelsolin proteins counteracts cancer cell invasion in vitro [64], however in cSCC, gelsolin and Flii have been the most studied to-date. Gelsolin over-expression has been shown to promote cell growth and motility in oral SCC [64,65], while Flii, through its effects on apoptosis, has been linked to promotion of breast cancer progression and invasion and progression of cSCC [23,66]. Flii is an important regulator of cell adhesion, migration and proliferation and a number of previous studies have described the role of Flii protein in wound healing and demonstrated the therapeutic effect of Flii neutralizing antibodies (FnAb) in acute and chronic wounds, skin blistering diseases and inflammatory skin conditions [25,32,[67][68][69][70][71][72].…”

“…Actin remodeling proteins have long been implicated in cSCC, as a dysregulated actin cytoskeleton and an aberrant tumor microenvironment is a hallmark of aggressive cSCC [11,93]. One particular actin remodeling protein, Flightless I (Flii), has been identified as a tumor promoter with transcriptional activity in colorectal, breast and hepatocellular carcinoma cell lines [66]. However, recent studies have also shown that Flii is significantly increased in human and mouse cSCC tissue samples, while secreted Flii is elevated in the sera of patients with cSCC and is increased in different cSCC cell lines established from human primary, recurring and metastatic cSCC as well as immortalized keratinocytes [23].…”