| Thyroid carcinoma is the most common malignant tumor in the endocrine system. The incidence of thyroid cancer has increased significantly in the past ten years. At present, the traditional methods for the treatment of thyroid cancer are thyroid surgery and postoperative treatment with radioactive iodine 131. Although most patients have a good prognosis after conventional treatment, there are still some patients with recurrence and distant metastasis, which may develop to the patients with the iodine refractory thyroid carcinoma. The treatment of such patients is extremely scarce, which is the greatest difficulty in clinical currently. Nowadays, using natural molecular compounds with anti-cancer activities has become a hot spot. Small molecular compounds extracted from food have many characteristics, including multiple targets, pharmacological anticancer activity, low toxicity and wide source, and they can make up some deficiencies of the traditional treatments. The research studied the inhibition of curcumin that is the active ingredient in turmeric on the growth of the thyroid carcinoma BCPAP cells, and the effect of the mechanism of endoplasmic reticulum stress on the cell death induced by curcumin. The research provided the theoretical basis for further study on the effect of curcumin on the thyroid carcinoma.Firstly, we found that curcumin with the concentrations ranging from 12.5 to 50 μmol/L for 24 h could inhibit cell growth and promote cell death by MTT assay and soft agar cloning experiment in the thyroid carcinoma BCPAP cells. The results of flow cytometry showed that 50 μmol/L curcumin could increase the concentration of cytosolic calcium and induce the endoplasmic reticulum expansion. These results showed that cell death induced by curcumin had close relationship with endoplasmic reticulum stress. The results of Western Blot and RT-PCR showed that with the treatment of 12.5-50 μmol/L curcumin for 24 h, ATF6, activating transcription factor, was significantly activated(P(27)0.05) and the m RNA(P(27)0.01) and protein(P(27)0.05) levels of CHOP, endoplasmic reticulum stress specific transcription factor, were up-regulated. Moreover, the splicing of nuclear transcription factor XBP-1 was significantly promoted(P(27)0.01), as well as the downstream target genes(P(27)0.05).Then the combined treatment of 4-phenylbutyrate, endoplasmic reticulum inhibitors, and curcumin could significantly inhibit the cell death of the thyroid carcinoma BCPAP cells induced by curcumin(P(27)0.01). In addition, 4-phenylbutyrate could significantly reverse the increasing of calcium and endoplasmic reticulum expansion induced by curcumin, and down-regulate the m RNA level of CHOP(P(27)0.05). These results further proved that curcumin could induce the death of the thyroid carcinoma BCPAP cells through inducing endoplasmic reticulum stress.Further experiments showed that using BAPTA-AM, the calcium ion chelating agents, could significantly reduce the rate of cell death induced by curcumin(P(27)0.05), and the rate of cell survival rose 8 percents, which indicated that calcium had an important role on the cell death through the endoplasmic reticulum stress.Endoplasmic reticulum stress could not only up-regulate the expression of the cell death related molecules to promote cell death, but also up-regulate the concentration of calcium to inhibit m TOR signaling pathway, promoting the expression of autophagy molecule related to m TOR and finally inducing autophagic death. The results of MTT assay, Western blot, RT-PCR and q PCR showed that curcumin could up-regulate the concentration of calcium to inhibit the expression of S6 related to the m TOR signaling pathway, inducing the autophagic death of BCPAP cells.In summary, the research confirmed the mechanism of cell death induced by curcumin in the thyroid carcinoma BCPAP cells. Curcumin activated ATF6/CHOP/XBP-1 signaling pathway through endoplasmic reticulum stress, and induced calcium overload which inhibited the expression of proteins related to m TOR pathway, up-regulated the expression of autophagy molecule regulated by m TOR, and ultimately promoted the cell death. |
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