Cervical cancer cells exhibit an increased requirement for
ubiquitin-dependent protein degradation associated with an elevated metabolic turnover rate.
Ubiquitin, which is a small, highly conserved
protein expressed in all eukaryotic cells, can be covalently linked to certain target
proteins to mark them for degradation by the
ubiquitin-
proteasome system. Previous studies highlight the essential role of
Ubiquitin B (UbB) and UbB-dependent proteasomal protein degradation in
histone deacetylase inhibitor (HDACi) -induced
tumor selectivity. We hypothesized that UbB plays a critical role in the function of
cervical cancer stem cells. We measured endogenous UbB levels in mammospheres in vitro by real-time PCR and Western blotting. The function of UbB in
cancer stem-like cells was assessed after knockdown of UbB expression in prolonged
Trichostatin A-selected HeLa cells (HeLa/
TSA) by measuring in vitro cell proliferation, cell apoptosis, invasion, and
chemotherapy resistance as well as by measuring in vivo growth in an orthotopic model of
cervical cancer. We also assessed the cancer stem cell frequency, tumorsphere formation, and in vivo growth of human
cervical cancer xenografts after UbB silencing. We found that HeLa/
TSA were resistant to
chemotherapy, highly expressed the UbB gene and the stem cell markers Sox2, Oct4 and Nanog. These cells also displayed induced differentiation abilities, including enhanced migration/invasion/
malignancy capabilities in vitro and in vivo. Furthermore, an elevated expression of UbB was shown in the
tumor samples of
chemotherapy patients. Silencing of UbB inhibited tumorsphere formation, lowered the expression of stem cell markers and decreased cervical xenograft growth. Our results demonstrate that UbB was significantly increased in prolonged
Trichostatin A-selected HeLa cells and it played a key role in the maintenance of
cervical cancer stem-like cells.