FBXL20-mediated Vps34 ubiquitination as a p53 controlled checkpoint in regulating autophagy and receptor degradation

Abstract

Vacuolar protein-sorting 34 (Vps34), the catalytic subunit in the class III PtdIns3 (phosphatidylinositol 3) kinase complexes, mediates the production of PtdIns3P, a key intracellular lipid involved in regulating autophagy and receptor degradation. However, the signal transduction pathways by which extracellular signals regulate Vps34 complexes and the downstream cellular mechanisms are not well understood. Here we show that DNA damageactivated mitotic arrest and CDK activation lead to the phosphorylation of Vps34, which provides a signal to promote its ubiquitination and proteasomal degradation mediated by FBXL20 (an F-box protein) and the associated Skp1 (S-phase kinase-associated protein-1)-Cullin1 complex, leading to inhibition of autophagy and receptor endocytosis. Furthermore, we show that the expression of FBXL20 is regulated by p53-dependent transcription. Our study provides a molecular pathway by which DNA damage regulates Vps34 complexes and its downstream mechanisms, including autophagy and receptor endocytosis, through SCF (Skp1-Cul1-F-box)-mediated ubiquitination and degradation. Since the expression of FBXL20 is regulated by p53-dependent transcription, the control of Vps34 ubiquitination and proteasomal degradation by FBXL20 and the associated SCF complex expression provides a novel checkpoint for p53 to regulate autophagy and receptor degradation in DNA damage response.

F-box protein interactions with the hallmark pathways in cancer

“…In addition to this transcriptional response, the recognition of Vps34 by Fbxl20 is also regulated via phosphorylation of Thr159 by cyclin B1/Cdk1, during normal mitosis and during mitotic arrest due to DNA damage (230). Thus p53 can impact on multiple aspects of autophagy, receptor signalling and intracellular traffic via SCF(Fbxl20)-mediated ubiquitination of Vps34.…”

“…Over-expression of Fbxl20 caused increased invasion and cell motility that correlated with decreased E-cadherin, and increased β-catenin levels, although no direct substrate was identified (229). A potential intermediary could be Vps34 which has recently been shown to be ubiquitinated by SCF(Fbxl20) and degraded by the proteasome (230).…”

The update on transcriptional regulation of autophagy in normal and pathologic cells: A novel therapeutic target

“…Under normal physiological conditions, proteins that stimulate autophagy flux are in a dominant position. In contrast, proteins that inhibit autophagy play the main function in various extreme situations [155][156][157]. The autophagy-related target genes of P53 include ATG2, ATG4, ATG7, ATG10, BCL2, ULK1, DRAM1, AMPK, and so on [152][153][154][155][156][157] (Table 1).…”

“…The reason for the above phenomenon is that P53 controls the expression of many autophagy-related proteins, which show the opposite function in regulating autophagy [154,155]. Certain proteins that are under the control of P53 (such as DNA damage regulated autophagy modulator 1, DRAM1) stimulate autophagy flux, whereas others (such as AMPK) inhibit mTOR pointing to P53 as a positive regulator of autophagy [156,157]. Under normal physiological conditions, proteins that stimulate autophagy flux are in a dominant position.…”

“…P53 operates within a broader regulatory network to define autophagic control [152][153][154][155][156][157]. When cells are subjected to oncogenic activation or genotoxic stress and P53 is activated, P53 is shown to induce autophagy [152,153].…”