ABSTRACT
Polycomb group (PcG) proteins play an important role in development and stem cell maintenance, and their dysregulation have been closely linked to oncogenesis and cancer stem cell phenotypes. Here, we found that nervous system polycomb 1 (NSPc1) was highly expressed in stem cell-like glioma cells (SLCs). Knockdown of NSPc1 in SLCs resulted in impaired neurosphere formation and self-renewal abilities, down-regulated expression of stemness markers such as NESTIN, CD133 and SOX2, and decreased capacity to propagate subcutaneous xenografts. In contrast, glioma cells overexpressing NSPc1 exhibited a stem cell-like phenotype, up-regulated expression of stemness markers NESTIN, CD133 and SOX2, and an enhanced capacity to propagate subcutaneous xenografts. Furthermore, we identified that NSPc1 epigenetically repressed the expression of retinol dehydrogenase 16 (RDH16) by directly binding to a region upstream (-1073 to -823) of the RDH16 promoter. Next, we confirmed that RDH16 is a stemness suppressor that partially rescues SLCs from the NSPc1-induced increase in neurosphere formation. Finally, we showed that ATRA partly reversed the NSPc1-induced stemness enhancement in SLCs, through mechanisms correlated with an ATRA-dependent decrease in the expression of NSPc1. Thus, our results demonstrate that NSPc1 promotes cancer stem cell self-renewal by repressing the synthesis of ATRA via targeting RDH16 and may provide novel targets for glioma treatment in the future.
Subject(s)
Alcohol Oxidoreductases/metabolism , Brain Neoplasms/metabolism , Glioma/metabolism , Neoplastic Stem Cells/metabolism , Polycomb Repressive Complex 1/metabolism , Tretinoin/metabolism , AC133 Antigen/metabolism , Alcohol Oxidoreductases/genetics , Animals , Brain Neoplasms/genetics , Brain Neoplasms/pathology , Cell Line, Tumor , Gene Expression Regulation, Neoplastic , Glioma/genetics , Glioma/pathology , Humans , Male , Mice , Mice, Inbred BALB C , Neoplastic Stem Cells/pathology , Nestin/genetics , Nestin/metabolism , Polycomb Repressive Complex 1/genetics , SOXB1 Transcription Factors/metabolismABSTRACT
A human promyelocytic leukemic cell line (HL-60 cells) was induced to differentiate along the myeloid pathway in vitro by 1.25% dimethylsulfoxide (DMSO) as an inducer. The membrane fluidity, the quantity of ConA binding sites on the cell membrane surface, and the protein tyrosine kinase (Tyr-PK) activity existing in NP-40 membrane extract and cytoplasma extract were determined respectively. The activity of tumour-derived immunosuppressive factor (TDSF) secreted by HL-60 cells into culture supernatant was also determined. The results demonstrated that: (1) HL-60 cells were capable of undergoing differentiation onto the myeloid pathway in the presence of DMSO. The growth of DMSO-treated HL-60 cells became slow and synthesis rate of DNA decreased by about 50%. (2) Both membrane fluidity and the quantity of ConA binding sites on membrane were obviously lower after induced with DMSO than those before induction. (3) The Tyr-PK activity in the NP-40 membrane extract increased during the period of induced differentiation. The phosphorylation level of endogenous protein in cytoplasma extract decreased with the process of induced differentiation. It may be reasoned that the phosphatase activity is much higher than the phosphorylase activity. (4) The secretive level of TDSF by HL-60 cells during the period of induced differentiation revealed no change. The preliminary results showed that the malignant phenotypes of tumour cells we used may undergo reversible changes with induced differentiation of tumour cells except the secretion of TDSF.
