Role of TGF-β1 in human breast cancer stem cells.

Objective: To investigate the auto-induction of transforming growth factor-b1 (TGF-β1) in breast cancer stem cells (BCSCs) and its effect on cell viability and stemness.

Methods: Human BCSCs (aldehyde dehydrogenase positive; ALDH+) were grown in serum-free Dulbecco's Modified Eagle Medium/Nutrient Mixture F12 (DMEM/F12) and treated for periods of 1, 2 and 4 hours with 0.1 ng/ml recombinant human TGF-β1 protein (rhTGF-β1). The medium was then replaced with serum-free DMEM/F12 without rhTGF-β1 for 24 hours. Cell viability was determined using a trypan blue exclusion assay. Type 1 TGF-β receptor (TβR1), TGF-β1, octamer-binding transcription factor 4 (OCT4) and aldehyde dehydrogenase 1 family member A1 (ALDH1A1) messenger RNA (mRNA) expression levels were analysed using quantitative real-time reverse-transcriptase polymerase chain reaction (RT-qPCR). The TGF-β protein level in the culture medium was determined using an enzyme-linked immunosorbent assay (ELISA).

Results: The expression levels of rhTGF-β1, TGF-β1 and TβR1 mRNA significantly increased in BCSCs compared to control after treatment for 1 and 2 hours but decreased after 4 hours. This is in line with alteration of stemness gene, OCT4 and ALDH1A1 mRNA expressions. However, the secretion of newly synthesised TGF-β1 significantly increased after 2 hours. In contrast, viable BCSCs decreased after 1 hour and then gradually increased 2.7 times compared to control after 4 hours.

Conclusions: TGF-β1 treatment in low concentration and for short period of time triggers its auto-induction in BCSCs, leading to increased cell viability and stemness gene expression via autocrine signalling.