HIF Signalling Modulates p53/ miR ‐145‐5p Axis in Hypoxia‐Driven Tumorigenesis of HepG2 Tumourspheres

Hypoxia is associated with increased tumour aggressiveness and relapses in hepatocellular carcinoma (HCC) through HIF signalling. Tumour suppressor p53, its deacetylase SIRT1 and liver-specific miRNAs are deregulated in hypoxia, further driving HCC tumorigenesis. The role of HIFs-p53-SIRT1-miRNAs in tumorigenesis of HepG2 tumourspheres under hypoxic conditions remains unexplored, hence is the focus of this study. HepG2 tumourspheres cultured under hypoxic and serum-free conditions for 19 days showed reduced proliferation and apoptosis, and increased pro-survival autophagy, CSC features and resistance. HIF-1α and HIF-2α proteins were stabilised in HepG2 tumourspheres cultured in hypoxia for up to 15 days compared to only up to 24 h in monolayer cells. p53 was activated in hypoxia, evidenced by significant increase in Ace-p53 expression and Ace-p53/total-p53 ratio, which were negatively correlated with HIF-1α/HIF-2α throughout hypoxia. Concurrently, nuclear p53 localisation was reduced in hypoxia, suggesting HIFs-suppression of p53 transcriptional activity. SIRT1 however, showed no correlation with p53 acetylation and HIF-1α/HIF-2α, with no notable changes in its nuclear-cytoplasmic localisation. Among the six selected miRNAs, miR-145-5p, -26a-5p and -375-3p were upregulated, miR-22-3p was downregulated, while miR-29c-3p and miR-34a-5p remained unchanged. miR-145-5p showed a negative correlation with p53 expression in hypoxia. Pharmacological inhibition of HIFs resulted in significant upregulation of p53 and miR-375-3p, while SIRT1, miR-145-5p and miR-26a-5p were downregulated. miR-145-5p was negatively correlated with p53 protein when HIFs were stabilised but positively correlated when HIFs were inhibited. This study highlights the role of HIFs/p53/miR-145-5p-associated regulation under hypoxic conditions in HepG2 tumourspheres, providing insights for future therapeutic exploration in HCC.