Sphere-forming cell subpopulations with cancer stem cell properties in human hepatoma cell lines

TLDR

Cancer stem cells are considered the drivers of tumor initiation and recurrence. The study aimed to isolate and characterize CSCs from human hepatoma cell lines by cultivating sphere‑forming cells in a stem cell‑conditioned medium to facilitate targeted therapeutic development. Researchers cultured PLC/PRF/5, MHCC97H, and HepG2 cells in stem cell‑conditioned medium to generate serially passaged, nonadherent 3‑D spheres, then evaluated their self‑renewal, proliferation, chemoresistance, tumorigenicity, and stem‑cell protein expression, and performed a stem‑cell RT‑PCR array. Sphere‑forming cells displayed hallmark CSC traits—including sustained self‑renewal, high proliferation, drug resistance, and overexpression of Oct3/4, OV6, EpCAM, CD133, and CD44—were tumorigenic even at 500 cells in NOD/SCID mice, and exhibited elevated CSL‑independent Notch signaling components DTX1 and Ep300, which were suppressed by the gamma‑secretase inhibitor MRK003.

Abstract

Cancer stem cells (CSCs) are regarded as the cause of tumor formation and recurrence. The isolation and identification of CSCs could help to develop novel therapeutic strategies specifically targeting CSCs.Human hepatoma cell lines were plated in stem cell conditioned culture system allowed for sphere forming. To evaluate the stemness characteristics of spheres, the self-renewal, proliferation, chemoresistance, tumorigenicity of the PLC/PRF/5 sphere-forming cells, and the expression levels of stem cell related proteins in the PLC/PRF/5 sphere-forming cells were assessed, comparing with the parental cells. The stem cell RT-PCR array was performed to further explore the biological properties of liver CSCs.The PLC/PRF/5, MHCC97H and HepG2 cells could form clonal nonadherent 3-D spheres and be serially passaged. The PLC/PRF/5 sphere-forming cells possessed a key criteria that define CSCs: persistent self-renewal, extensive proliferation, drug resistance, overexpression of liver CSCs related proteins (Oct3/4, OV6, EpCAM, CD133 and CD44). Even 500 sphere-forming cells were able to form tumors in NOD/SCID mice, and the tumor initiating capability was not decreased when spheres were passaged. Besides, downstream proteins DTX1 and Ep300 of the CSL (CBF1 in humans, Suppressor of hairless in Drosophila and LAG1 in C. elegans) -independent Notch signaling pathway were highly expressed in the spheres, and a gamma-secretase inhibitor MRK003 could significantly inhibit the sphere formation ability.Nonadherent tumor spheres from hepatoma cell lines cultured in stem cell conditioned medium possess liver CSC properties, and the CSL-independent Notch signaling pathway may play a role in liver CSCs.