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Molecular pathways involved in the antineoplastic effects of calcitriol on insulinoma cells
Francesca Galbiati1, Luca Polastri, Bernard Thorens
1Division of General Medicine, Unit of Endocrinology and Metabolic Disease, San Raffaele Scientific Institute, 20132 Milan, Italy.
Abstract:
We have previously reported that in tumorigenic pancreatic beta-cells, calcitriol exerts a potent antitumorigenic effect by inducing apoptosis, cell growth inhibition, and reduction of solid beta-cell tumors. Here we have studied the molecular pathways involved in the antineoplastic activity of calcitriol on mouse insulinoma beta TC(3) cells, mouse insulinoma beta TC expressing or not expressing the oncogene p53, and beta TC-tet cells overexpressing or not the antiapoptotic gene Bcl2. Our results indicate that calcitriol-induced apoptosis was dependent on the function of p53 and was associated with a biphasic increase in protein levels of transcription factor nuclear factor-kappa B. Calcitriol decreased cell viability by about 40% in p53-retaining beta TC and in beta TC(3) cells; in contrast, beta TC p53(-/-) cells were only minimally affected. Calcitriol-induced cell death was regulated by members of the Bcl-2 family of apoptosis regulatory proteins, as shown by calcitriol-induced up-regulation of proapoptotic Bax and Bak and the lack of calcitriol-induced cytotoxicity in Bcl-2-overexpressing insulinoma cells. Moreover, calcitriol-mediated arrest of beta TC(3) cells in the G(1) phase of the cell cycle was associated with the abnormal expression of p21 and G(2)/M-specific cyclin B2 genes and involved the DNA damage-inducible factor GADD45. Finally, in beta TC(3) cells, calcitriol modulated the expression of IGF-I and IGF-II genes. In conclusion, these findings contribute to the understanding of the antitumorigenic effects of calcitriol on tumorigenic pancreatic beta-cells and further support the rationale of its utilization in the treatment of patients with malignant insulinomas.
Insights
Calcitriol, a vitamin D hormone, effectively combats pancreatic beta-cell tumors by triggering programmed cell death (apoptosis). Its anti-cancer effects are linked to p53 gene function and Bcl-2 family proteins, offering potential for malignant insulinoma treatment.
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- Calcitriol (active vitamin D) demonstrates antitumorigenic properties in pancreatic beta-cells.
- Previous studies showed calcitriol reduces tumor growth, inhibits cell proliferation, and induces apoptosis in beta-cells.
- The precise molecular mechanisms underlying calcitriol's antineoplastic activity require further elucidation.
Purpose of the Study:
- To investigate the molecular pathways mediating calcitriol's antineoplastic effects in pancreatic beta-cell models.
- To assess the role of p53 and Bcl-2 family proteins in calcitriol-induced apoptosis and cell death.
- To explore calcitriol's impact on cell cycle regulation and gene expression in insulinoma cells.
Main Methods:
- Utilized mouse insulinoma beta TC(3) cells, p53-expressing/non-expressing variants, and Bcl-2 overexpressing beta TC-tet cells.
- Assessed apoptosis, cell viability, cell cycle progression, and gene expression (p53, Bcl-2, Bax, Bak, p21, cyclin B2, GADD45, IGF-I, IGF-II, NF-κB).
- Analyzed calcitriol's effects on protein levels of transcription factor nuclear factor-kappa B (NF-κB).
Main Results:
- Calcitriol-induced apoptosis was dependent on p53 function and associated with increased NF-κB levels.
- Cell viability decreased significantly in p53-positive cells, while p53-deficient cells showed minimal response.
- Calcitriol upregulated pro-apoptotic Bax and Bak, and its cytotoxicity was diminished in Bcl-2 overexpressing cells, indicating Bcl-2 family regulation.
- Cell cycle arrest at G1 phase was observed, linked to altered p21, cyclin B2, and GADD45 expression.
- Calcitriol modulated IGF-I and IGF-II gene expression in beta TC(3) cells.
Conclusions:
- Calcitriol's antitumorigenic effects on tumorigenic pancreatic beta-cells are mediated by p53-dependent apoptosis and regulation of Bcl-2 family proteins.
- Calcitriol influences cell cycle progression and modulates specific gene expressions, including IGF-I and IGF-II.
- These findings support the potential use of calcitriol in treating malignant insulinomas.