We previously reported that endogenous Sprouty-related, EVH1 domain-containing protein 2 (SPRED2), an inhibitor of the Ras/Raf/ERK-MAPK pathway, controls hepatocellular carcinoma (HCC) cell stemness by downregulating the expression of pluripotency factors, such as Nanog, c-Myc, and KLF4, in an ERK-dependent fashion. However, the exact mechanisms by which SPRED2 regulates HCC cell stemness have not been established.

Three human HCC cell lines [HepG2 (parental and SPRED2-deficient), HLE, and Hep3B] were used. Cells were transfected to downregulate or overexpress proteins. Western blot and RT-qPCR were used to evaluate the level of protein and mRNA expression. Co-immunoprecipitation and ChIP-qPCR were used to examine protein-protein interactions and the activation of gene transcription. Clinical HCC tissues were also used to validate in vitro data.

KLF4 was identified as the major pluripotency factor responsible for SPRED2-mediated downregulation of HCC cell stemness and KLF4 expression was regulated by miR-506-3p. SPRED2 formed a protein complex with the tumor suppressor (p53) and upregulated miR-506 gene transcription by binding to the promoter region, resulting in subsequent downregulation of KLF4 mRNA expression. There was a negative correlation between KLF4 expression and miR-506-3p and a positive correlation between miR-506-3p expression and SPRED2 in human HCC samples, highlighting the relevance of the study findings.

The current study revealed a novel SPRED2/p53/miR-506-3p/KLF4 axis through which SPRED2 contributes to the suppression of HCC cell stemness and provides a potential new target to prevent HCC progression.