Background
The genesis and developments of solid tumors, analogous to the renewal of healthy tissues, are driven by a subpopulation of dedicated stem cells, known as cancer stem cells (CSCs), that exhibit long-term clonal repopulation and self-renewal capacity. CSCs may regulate tumor initiation, growth, dormancy, metastasis, recurrence and chemoresistance. While autophagy has been proposed as a regulator of the stemness of CSCs, the underlying mechanisms requires further elucidation.
Conclusion
This study has elucidated a new mechanism underlying the regulation of autophagy on stemness, i.e. CSCs can exploit the SEC23A/ER-stress/FAM134B/ER-phagy axis for the self-renewal. These observations provide new ideas for exploration of the regulatory network of CSC self-renewal to develop CSCs-based therapy strategies for malignant tumors. Video Abstract.
Methods
The CSC component in human melanoma cell lines M14 and A375 was isolated and purified by repetitive enrichments for cells that consistently display anchorage-independent spheroid growth. The stemness properties of the CSCs were confirmed in vitro by the expressions of stemness marker genes, the single-cell cloning assay and the serial spheroid formation assay. Subcutaneous tumor transplantation assay in BALB/c nude mice was performed to test the stemness properties of the CSCs in vivo. The autophagic activity was confirmed by the protein level of LC3 and P62, mRFP-LC3B punta and cytoplasmic accumulation of autolysosomes. The morphology of ER was detected with transmission electron microscopy.
Results
In the present study, by employing stable CSC cell lines derived from human melanoma cell lines M14 and A375, we show for the first time that Sec23a inhibits the self-renewal of melanoma CSCs via inactivation of ER-phagy. Mechanistically, inhibition of Sec23a reduces ER stress and consequently FAM134B-induced ER-phagy. Furthermore, TCGA data mining and analysis show that Sec23a is a favorable diagnostic and prognostic marker for human skin cutaneous melanoma.