PDP1 drives hepatocellular carcinoma progression by regulating senescence through the cAMP/Ca2+ signaling pathway.

PDP1 is upregulated in HCC patients and is significantly associated with poor prognosis.

• PDP1 expression was found to be elevated in hepatocellular carcinoma tissue compared to non-tumor tissue.
• High PDP1 expression correlated with poor clinical outcomes in HCC patients.
• The association between PDP1 upregulation and prognosis was statistically significant.

PDP1 induces cellular senescence in HCC and activates senescence-associated pathways including p16 and p21.

• PDP1 functionally induced cellular senescence in HCC cells.
• Xenograft models demonstrated activation of senescence-associated pathways including p16 and p21 in PDP1-expressing tumors.
• PDP1 promoted senescence-associated secretory phenotype (SASP)-driven downstream effects.

PDP1 activates the cAMP/Ca2+ signaling pathway to promote SASP-driven EMT, stemness, and malignant progression.

• PDP1 activated cyclic adenosine monophosphate (cAMP)/Ca2+ signaling in HCC cells.
• Activation of this pathway promoted epithelial-mesenchymal transition (EMT) and cancer stemness.
• In vivo xenograft models confirmed cAMP and Ca2+ pathway activation accompanying PDP1-enhanced tumor growth.

ADCY5 is identified as a critical downstream mediator of PDP1 effects and a major source of intracellular cAMP production.

• Adenylyl cyclase 5 (ADCY5) is a membrane-associated enzyme responsible for catalyzing ATP into cAMP.
• ADCY5 was identified as the primary downstream effector through which PDP1 exerts its pro-tumorigenic effects.
• ADCY5 served as the major source of intracellular cAMP production in the context of PDP1-driven signaling.

PDP1 suppression enhances glycolysis and increases histone H3 lysine 18 lactylation (H3K18la), leading to DNMT1 activation.

• Loss of PDP1 function resulted in enhanced glycolytic activity in HCC cells.
• Enhanced glycolysis led to increased H3K18la, a lactate-derived epigenetic modification.
• Elevated H3K18la activated DNA methyltransferase 1 (DNMT1), the primary enzyme maintaining DNA methylation patterns.

DNMT1 activation following PDP1 suppression causes ADCY5 promoter hypermethylation and transcriptional silencing.

• DNMT1 activation downstream of H3K18la led to hypermethylation of the ADCY5 promoter.
• ADCY5 promoter hypermethylation resulted in transcriptional silencing of ADCY5.
• This epigenetic silencing of ADCY5 represents the mechanistic link between glycolytic changes and cAMP/Ca2+ signaling suppression upon PDP1 loss.

Glycolysis inhibition restores senescence and reverses PDP1-driven malignant phenotypes.

• Pharmacological inhibition of glycolysis was sufficient to restore cellular senescence in PDP1-expressing HCC cells.
• Glycolysis inhibition reversed the malignant phenotypes driven by PDP1, including EMT and stemness.
• These findings functionally link the glycolytic axis to PDP1-driven tumor progression.

PDP1 enhances tumor growth in vivo in xenograft models.

• Xenograft experiments demonstrated that PDP1 expression promoted tumor growth in vivo.
• In vivo tumors showed activation of senescence-associated pathways (p16, p21) and cAMP/Ca2+ signaling.
• These in vivo findings corroborated the mechanistic observations made in vitro.