FAT1 inhibits AML autophagy and proliferation via downregulating ATG4B expression

Background: Emerging studies have shown that FAT atypical cadherin 1 (FAT1) and autophagy separately inhibits and promotes acute myeloid leukemia (AML) proliferation. However, it is unknown whether FAT1 were associated with autophagy in regulating AML proliferation.Methods: AML cell lines, 6-week-old male nude mice and AML patient samples were used in this study. qPCR/ Western blot and cell viability/3H-TdR incorporation assays were separately used to detect mRNA/protein levels and cell activity/proliferation. Luciferase reporter assay was used to examine gene promoter activity. Co-IP analysis was used to detect the binding of proteins.Results: In this study, we for the first time demonstrated that FAT1 inhibited AML proliferation by decreasing AML autophagy level. Moreover, FAT1 weakened AML autophagy level via decreasing autophagy related 4B (ATG4B) expression. Mechanistically, we found that FAT1 reduced the phosphorylated and intranuclear SMAD family member 2/3 (smad2/3) protein levels, thus decreasing the activity of ATG4B gene promoter. Further-more, we found that FAT1 competitively bound to TGF-beta R II which decreased the binding of TGF-beta R II to TGF-beta R I and the subsequent phosphorylation of TGF-beta R I, thus reducing the phosphorylation and intranuclear smad2/3. The experiments in nude mice showed that knockdown of FAT1 promoted AML autophagy and proliferation in vivo.Conclusions: Collectively, these results revealed that FAT1 downregulates ATG4B expression via inhibiting TGF beta-smad2/3 signaling activity, thus decreasing the autophagy level and proliferation activity of AML cells. General significance: Our study suggested that the FAT1-TGF beta-smad2/3-ATG4B-autophagy pathway may be a novel target for developing new targeted drugs to AML treatment.

Automated summary

In this study, it was demonstrated for the first time that FAT1 inhibited AML proliferation by reducing autophagy level. FAT1 achieved this by decreasing the expression of ATG4B, which is related to autophagy. Mechanistically, FAT1 decreased the levels of phosphorylated and intranuclear smad2/3, thus decreasing the activity of the ATG4B gene promoter. It was also found that FAT1 competitively bound to TGF-beta R II, leading to reduced phosphorylation of TGF-beta R I and smad2/3. Knockdown of FAT1 promoted AML autophagy and proliferation in vivo.