Elevated FBXL6 expression in hepatocytes activates VRK2-transketolase-ROS-mTOR-mediated immune evasion and liver cancer metastasis in mice.

Metastatic hepatocellular carcinoma (HCC) is the most lethal malignancy and lacks effective treatment. FBXL6 is overexpressed in human hepatocellular carcinoma (HCC), but whether this change drives liver tumorigenesis and lung metastasis in vivo remains unknown. In this study, we aimed to identify FBXL6 (F-Box and Leucine Rich Repeat Protein 6) as a key driver of HCC metastasis and to provide a new paradigm for HCC therapy. We found that elevated FBXL6 expression in hepatocytes drove HCC lung metastasis and was a much stronger driver than Kras mutation (KrasG12D/+;Alb-Cre), p53 haploinsufficiency (p53+/-) or Tsc1 loss (Tsc1fl/fl;Alb-Cre). Mechanistically, VRK2 promoted Thr287 phosphorylation of TKT and then recruited FBXL6 to promote TKT ubiquitination and activation. Activated TKT further increased PD-L1 and VRK2 expression via the ROS-mTOR axis, leading to immune evasion and HCC metastasis. Targeting or knockdown of TKT significantly blocked FBXL6-driven immune evasion and HCC metastasis in vitro and in vivo. Notably, the level of active TKT (p-Thr287 TKT) was increased and was positively correlated with the FBXL6 and VRK2 expression levels in HCC patients. Our work provides novel mechanistic insights into FBXL6-driven HCC metastasis and suggests that targeting the TKT-ROS-mTOR-PD-L1/VRK2 axis is a new paradigm for treating patients with metastatic HCC with high FBXL6 expression.

Zhang J ，Lin XT ，Yu HQ ，Fang L ，Wu D ，Luo YD ，Zhang YJ ，Xie CM ... -  《-》

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

Kirsten rat sarcoma (KRAS) and mutant KRASG12D 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 KRASG12D activity in hepatocellular carcinoma (HCC). We constructed transgenic mouse strains LC (LSL-Fbxl6KI/+;Alb-Cre, n = 13), KC (LSL-KrasG12D/+;Alb-Cre, n = 10) and KLC (LSL-KrasG12D/+;LSL-Fbxl6KI/+;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 KRASG12D at lysine 128, leading to the activation of both KRAS and KRASG12D 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 KRASG12D 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 (χ2 = 85.067, P < 0.001), p-mTOR (χ2 = 66.919, P < 0.001) and PRELID2 (χ2 = 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 KRASG12D 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 KRASG12D-induced tumorigenesis, providing a potential therapeutic strategy to treat this aggressive subtype of liver cancer.

Xiong HJ ，Yu HQ ，Zhang J ，Fang L ，Wu D ，Lin XT ，Xie CM ... -  《-》

Deciphering the molecular interplay and tumorigenesis in hepatocellular carcinoma through insights into FBXL6 and KRAS(G12D).

Cai Q ，Shubhra QTH 《-》

Elevated FBXW10 drives hepatocellular carcinoma tumorigenesis via AR-VRK2 phosphorylation-dependent GAPDH ubiquitination in male transgenic mice.

Hepatocellular carcinoma (HCC), the most common liver cancer, occurs mainly in men, but the underlying mechanism remains to be further explored. Here, we report that ubiquitinated glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is responsible for HCC tumorigenesis in males. Mechanistically, FBXW10 promotes GAPDH polyubiquitination and activation; VRK2-dependent phosphorylation of GAPDH Ser151 residue is critical for GAPDH ubiquitination and activation. Activated GAPDH interacts with TRAF2, leading to upregulation of the canonical and noncanonical NF-κB pathways, and increases PD-L1 and AR-VRK2 expression, followed by induction of immune evasion, HCC tumorigenesis, and metastasis. Notably, the GAPDH inhibitor koningic acid (KA) activates immune response and protects against FBXW10-driven HCC in vivo. In HCC clinical samples, the expression of active GAPDH is positively correlated with that of FBXW10 and VRK2. We propose that the FBXW10/AR/VRK2/GAPDH/NF-κB axis is critical for HCC tumorigenesis in males. Targeting this axis with KA is a potential therapeutic strategy for male HCC patients.

Lin XT ，Zhang J ，Liu ZY ，Wu D ，Fang L ，Li CM ，Yu HQ ，Xie CM ... -  《-》

Transketolase (TKT) activity and nuclear localization promote hepatocellular carcinoma in a metabolic and a non-metabolic manner.

Qin Z ，Xiang C ，Zhong F ，Liu Y ，Dong Q ，Li K ，Shi W ，Ding C ，Qin L ，He F ... -  《-》