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.