Elevated FBXL6 activates both wild-type KRAS and mutant KRAS G12D and drives HCC tumorigenesis via the ERK/mTOR/PRELID2/ROS axis in mice

• Published in: Military medical research Vol. 10; no. 1; p. 68
• Main Authors: Xiong, Hao-Jun, Yu, Hong-Qiang, Zhang, Jie, Fang, Lei, Wu, Di, Lin, Xiao-Tong, Xie, Chuan-Ming
• Format: Journal Article
• Language: English
• Published: England 20.12.2023
• Subjects: Animals; Carcinogenesis; Carcinoma, Hepatocellular - genetics; Extracellular Signal-Regulated MAP Kinases - metabolism; Humans; Liver Neoplasms - genetics; Mammals - metabolism; Mice; Mitogen-Activated Protein Kinase Kinases - metabolism; Pancreatic Neoplasms - metabolism; Pancreatic Neoplasms - pathology; Proto-Oncogene Proteins p21(ras) - genetics; Proto-Oncogene Proteins p21(ras) - metabolism; Reactive Oxygen Species - metabolism; TOR Serine-Threonine Kinases - metabolism; Extracellular signal-regulated kinase (ERK); PRELID2; Reactive oxygen species; Ubiquitination; Kirsten rat sarcoma (KRAS); F-box and leucine-rich repeat 6 (FBXL6); Mammalian target of rapamycin
• ISSN: 2054-9369

Kirsten rat sarcoma (KRAS) and mutant KRAS have been implicated in human cancers, but it remains unclear whether their activation requires ubiquitination. This study aimed to investigate whether and how F-box and leucine-rich repeat 6 (FBXL6) regulates KRAS and KRAS activity in hepatocellular carcinoma (HCC). We constructed transgenic mouse strains LC (LSL-Fbxl6 ;Alb-Cre, n = 13), KC (LSL-Kras ;Alb-Cre, n = 10) and KLC (LSL-Kras ;LSL-Fbxl6 ;Alb-Cre, n = 12) mice, and then monitored HCC for 320 d. Multiomics approaches and pharmacological inhibitors were used to determine oncogenic signaling in the context of elevated FBXL6 and KRAS activation. Co‑immunoprecipitation (Co-IP), Western blotting, ubiquitination assay and RAS activity detection assay were employed to investigate the underlying molecular mechanism by which FBXL6 activates KRAS. The pathological relevance of the FBXL6/KRAS/extracellular signal-regulated kinase (ERK)/mammalian target of rapamycin (mTOR)/proteins of relevant evolutionary and lymphoid interest domain 2 (PRELID2) axis was evaluated in 129 paired samples from HCC patients. FBXL6 is highly expressed in HCC as well as other human cancers (P < 0.001). Interestingly, FBXL6 drives HCC in transgenic mice. Mechanistically, elevated FBXL6 promotes the polyubiquitination of both wild-type KRAS and KRAS at lysine 128, leading to the activation of both KRAS and KRAS and promoting their binding to the serine/threonine-protein kinase RAF, which is followed by the activation of mitogen-activated protein kinase kinase (MEK)/ERK/mTOR signaling. The oncogenic activity of the MEK/ERK/mTOR axis relies on PRELID2, which induces reactive oxygen species (ROS) generation. Furthermore, hepatic FBXL6 upregulation facilitates KRAS to induce more severe hepatocarcinogenesis and lung metastasis via the MEK/ERK/mTOR/PRELID2/ROS axis. Dual inhibition of MEK and mTOR effectively suppresses tumor growth and metastasis in this subtype of cancer in vivo. In clinical samples, FBXL6 expression positively correlates with p-ERK (χ  = 85.067, P < 0.001), p-mTOR (χ  = 66.919, P < 0.001) and PRELID2 (χ  = 20.891, P < 0.001). The Kaplan-Meier survival analyses suggested that HCC patients with high FBXL6/p-ERK levels predicted worse overall survival (log‑rank P < 0.001). FBXL6 activates KRAS or KRAS via ubiquitination at the site K128, leading to activation of the ERK/mTOR/PRELID2/ROS axis and tumorigenesis. Dual inhibition of MEK and mTOR effectively protects against FBXL6- and KRAS -induced tumorigenesis, providing a potential therapeutic strategy to treat this aggressive subtype of liver cancer.