Roles of SIRT1/FoxO1/SREBP-1 in the development of progestin resistance in endometrial cancer.

PURPOSE: The prevalence of endometrial cancer (EC) is increasing worldwide. Progestin therapy is effective for both early stage EC patients who require preserving fertility and advanced or recurrent patients. Progestin resistance resulting from downregulation of progesterone receptor (PR) remains a major problem, and its mechanism is currently unclear. It was demonstrated that Sirtuin 1 (SIRT1), forkhead transcription factor 1 (FoxO1) and sterol regulatory element binding protein-1 (SREBP-1) may act as a pathway and play crucial roles in the development of EC in our previous studies. In the present study, we investigated the effect on the development of progestin resistance and the relationship with PR of SIRT1/FoxO1/SREBP-1.

METHODS: A progestin-resistant Ishikawa cell line was established in the stimulation and selection of medroxyprogesterone acetate (MPA), and the resistance was analyzed by MTT assay, flow cytometry, and Transwell invasion assay. qRT-PCR and western blotting were conducted to detect the expression of SIRT1, FoxO1, SREBP-1 and PR. SIRT1 knockdown progestin-resistant cells were established by lentiviral transduction.

RESULTS: The new progestin-resistant cell line presented sufficient resistance to MPA in aspects of proliferation, distribution of cell cycle and apoptosis compared with original Ishikawa cells. Besides, the invasion capability of progestin-resistant cells was observably increased. In both protein and mRNA levels, SIRT1 and SREBP-1 were upregulated in progestin-resistant cells, while PR and FoxO1 were downregulated. SIRT1 was knocked down by lentivirus transfection in progestin-resistant cells, resulting in upregulation of PR, FoxO1 and downregulation of SREBP-1, thereby SIRT1 knockdown cells were more sensitive to MPA compared with progestin-resistant cells.

CONCLUSION: SIRT1/FoxO1/SREBP-1 act as a pathway targeting PR and involve in the development of progestin resistance in Ishikawa cells.