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Abstract F-box and WD repeat domain containing 7 (FBXW7) acts as a substrate receptor of SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase and plays crucial roles in the regulation of several cellular processes, including cell growth, division, and differentiation, by targeting diverse key regulators for degradation. However, its role in regulating cellular senescence remains elusive. Here, we found that FBXW7 inactivation by siRNA-based knockdown or CRISPR/Cas9-based knockout induced significant cellular senescence in p53 wild-type cells, but not in p53 mutant or null cells, along with activation of both the p53/p21 and p16INK4a/Rb pathways. Simultaneous p53 inactivation abrogated senescence and cell growth arrest induced by FBXW7 deficiency as well as the alteration of both the p53/p21 and p16INK4a/Rb pathways. Moreover, Fbxw7 deletion accelerated replicative senescence of primary mouse embryonic fibroblasts in a p53-dependent manner. In addition, FBXW7 deletion induced the senescence-associated secretory phenotype to trigger secondary senescence. Importantly, in a radiation-induced senescence mouse model, simultaneous deletion of p53 rescued accelerated senescence and aging caused by Fbxw7 loss. Thus, our study uncovered a novel role for FBXW7 in the regulation of senescence by eliminating p53.

Abstract F-box and leucine-rich repeat protein 7 (FBXL7), an F-box protein responsible for substrate recognition by the SKP1-Cullin-1-F-box (SCF) ubiquitin ligases, plays an emerging role in the regulation of tumorigenesis and tumor progression. FBXL7 promotes polyubiquitylation and degradation of diverse substrates and is involved in many biological processes, including apoptosis, cell proliferation, cell migration and invasion, tumor metastasis, DNA damage, glucose metabolism, planar cell polarity, and drug resistance. In this review, we summarize the downstream substrates and upstream regulators of FBXL7. We then discuss its role in tumorigenesis and tumor progression as either an oncoprotein or a tumor suppressor, and further describe its aberrant expression and association with patient survival in human cancers. Finally, we provide future perspectives on validating FBXL7 as a cancer biomarker for diagnosis and prognosis and/or as a potential therapeutic target for anticancer treatment.

Abstract ErbB2, a classical receptor tyrosine kinase, is frequently overexpressed in breast cancer cells. Although the role of ErbB2 in the transmission of extracellular signals to intracellular matrix has been widely studied, the functions of nuclear ErbB2 remain largely elusive. Here, we report a novel function of nuclear ErbB2 in repressing the transcription of DEPTOR, a direct inhibitor of mTOR. Nuclear ErbB2 directly binds to the consensus binding sequence in the DEPTOR promoter to repress its transcription. The kinase activity of ErbB2 is required for its nuclear translocation and transcriptional repression of DEPTOR. Moreover, the repressed DEPTOR by nuclear ErbB2 inhibits the induction of autophagy by activating mTORC1. Thus, our study reveals a novel mechanism for autophagy regulation by functional ErbB2, which translocates to the nucleus and acts as a transcriptional regulator to suppress DEPTOR transcription, leading to activation of the PI3K/AKT/mTOR pathway to inhibit autophagy.