Loss of FCN3 links cirrhotic matrix stiffness to YAP activation in HCC

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Abstract Background Cirrhosis-associated matrix stiffness is a major biophysical driver of hepatocellular carcinoma (HCC). How fibrosis-induced stiffness activates oncogenic YAP signaling remains unclear. We investigated the role of ficolin-3 (FCN3) in stiffness-associated regulation of the O-GlcNAc transferase (OGT)–YAP axis in HCC. Methods Public transcriptomic datasets comparing cirrhotic and normal liver tissues (GSE114564), as well as HCC tissues from patients with and without cirrhosis (GSE14520), were analyzed. FCN3 protein expression was evaluated in 67 paired HCC and adjacent non-tumorous tissues, and a subset of 20 matched cases was further analyzed by quantitative reverse-transcription PCR and atomic force microscopy. Controlled-stiffness substrates, FCN3 gain- and loss-of-function models, and murine H22 allograft and human HepG2 xenograft models were used for functional validation. Mechanistic studies included RNA sequencing, cycloheximide chase assays, subcellular fractionation, co-immunoprecipitation, structural prediction, YAP-S127A rescue, Thiamet-G treatment, and YAP knockdown. Results FCN3 was downregulated in cirrhotic liver and HCC with cirrhosis. In clinical samples, tumor stiffness inversely correlated with FCN3 expression. FCN3 overexpression curtailed proliferation, clonogenicity, migration, and invasion in vitro and suppressed tumor growth in vivo. Transcriptomics revealed YAP pathway inhibition without changes in upstream kinases. FCN3 did not alter YAP mRNA but reduced YAP protein, increased p-YAP(S127), limited nuclear YAP, and shortened YAP half-life. Co-IP showed FCN3 binds OGT and disrupts OGT–YAP association, decreasing YAP O-GlcNAcylation. YAP knockdown partially attenuated FCN3’s anti-tumor effects. Conclusions These findings support a stiffness-associated FCN3–OGT–YAP regulatory model in HCC, in which FCN3 expression is associated with reduced OGT–YAP interaction, decreased YAP O-GlcNAcylation, and restricted YAP nuclear activity. Further studies are required to establish direct molecular competition and its independence from canonical Hippo–LATS signaling.