Effects of 25-hydroxyvitamin D3 on cell growth and cell death via regulation of the vitamin D metabolising system in a cervical adenocarcinoma cell line

Abstract

Cervical cancer is the leading cause of cancer-related mortalities in South African women. Vitamin D and its metabolites exert anti-cancer actions in various cancers; however, few studies have explored the effects of vitamin D in cervical cancer.

The vitamin D metabolising system (VDMS) is responsible for the activation and breakdown of the vitamin. Vitamin D is activated by two hydroxylation steps facilitated by 25-hydroxylase (CYP27A1/CYP2R1) and 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1). The resulting active hormone, 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), binds vitamin D receptor (VDR) in target cells to exert its effects. Both 1,25(OH)2D3 and its precursor 25(OH)D3 are catabolised by 24-hydroxylase (CYP24A1). This study aimed to use the cervical cancer cell line, HeLa treated with 25(OH)D3, to investigate the cell health parameters (cell count, viability, and cell cycle), cell death (apoptosis, autophagy and necrosis) by brightfield and transmission electron microscopy, and flow cytometry, and regulation of expression of genes and proteins in the VDMS by qPCR and Western blot.

Results indicated that treatment with 5000 nM 25(OH)D3 significantly decreased cell count and viability and increased the sub-G1 population without inducing cell cycle arrest. Treatment-induced intrinsic apoptosis through disruption of mitochondrial membrane potential, externalisation of phosphatidylserines and activation of executioner caspases -3 and -7. Classic morphological features of apoptosis were also observed with brightfield and transmission electron microscopy. In addition, high-dose treatment with vitamin D increased CYP27B1, CYP24A1 and VDR gene and protein expression. Interestingly, multinucleated cells were observed in all cultures, but the cells were significantly larger following high dose 25(OH)D3 treatment.

Collectively, the findings indicate that the VDMS acts in an autocrine manner to mediate the effects of supraphysiological doses of 25(OH)D3 on the growth and death of HeLa cells. Based on the data, it can be inferred that 25(OH)D3 holds promise as a therapeutic agent for cervical cancer treatment, and further clinical studies are warranted to explore this potential.