Role of local bioactivation of vitamin D by CYP27A1 and CYP2R1 in the control of cell growth in normal endometrium and endometrial carcinoma

Abstract

Vitamin D (VD) deficiency has been suggested as a risk factor for cancer. One recognized mechanism is that the low-serum 25-hydroxyvitamin D (25(OH)D) of VD deficiency reduces intratumoral 25(OH)D conversion to 1a,25-dihydroxyvitamin D (1,25D, the hormonal form of VD), compromising 1,25D-VD receptor (VDR) antitumoral actions. Reduced tumoral VDR and increased CYP24A1, the enzyme that degrades 1,25D and 25(OH)D, further worsen cancer progression. Importantly, in cells expressing CYP27A1 and/or CYP2R1, which convert inert VD into 25(OH)D, low-serum VD may reduce intratumoral 25(OH)D synthesis thereby compromising VDR antitumoral actions because 25(OH)D can activate the VDR directly and enhance 1,25D-VDR action. Therefore, this study examined whether abnormal endometrial expression of CYP27A1 and/or CYP2R1 may impair VDR-antiproliferative properties in endometrial carcinoma (EC). Immunohistochemical analysis of tissue microarrays of normal human endometrium (NE; n ¼ 60) and EC (n ¼ 157) showed the expected lower VDR expression in EC (P ¼ 0.0002). Instead, CYP24A1 expression was lower in EC compared with NE, while CYP27A1 and CYP2R1 expressions were higher (P ¼ 0.0002; P ¼ 0.03). Furthermore, in NE and EC, CYP2R1 and CYP27A1 expression correlated directly with nuclear VDR levels, an indicator of ligand-induced VDR activation, and inversely with the proliferation marker Ki67. Accordingly, in the endometrioid carcinoma cell lines IK, RL95/2 and HEC1-A, which express VDR, CYP27A1, and CYP2R1, VD efficaciously reduced cell viability and colony number, with a time course that paralleled actual increases in both intracellular 25(OH)D and nuclear VDR levels. Thus, VD may protect from EC progression in part through increased intratumoral 25(OH)D production by CYP27A1 and CYP2R1 for autocrine/paracrine enhancement of 1,25D-VDR-antiproliferative actions. Endometrial carcinoma (EC) results from neoplastic transformation of normal endometrium (NE) 1 leading to two main clinicopathological variants: endometrioid carcinoma (EEC) and non-endometrioid carcinomas (NEEC). EECs are estrogen-related tumors, frequently well differentiated, and developing mostly in peri-and postmenopausal women. Low grades (1 and 2) tumors are usually confined to the uterus (stage I) while grade 3 EECs are less frequent, with a higher tendency for extrauterine spread. NEEC, either serous or clear cell (CC) carcinomas, occur in older women, are estrogenunrelated tumors, with aggressive behavior and frequent extrauterine spread to the peritoneum or lymph nodes. 2,3 One risk factor for human cancer that can be safely modified is vitamin D (VD) deficiency/insufficiency.

Vitamin D and Endometrium: A Systematic Review of a Neglected Area of Research

“…In this case, tissue samples in different phases of the endometrial cycle were obtained from 60 women (age ranged from 25 to 55, mean = 43, 20 samples in proliferative and 40 samples in secretory phase), samples were embedded in paraffin blocks and tissue microarrays were analyzed. A decrease in the total expression of VDR in the proliferative endometrium compared with the secretory phase (fold change 3.17, p = 0.00002) as well as an increase in the cytosolic VDR protein expression (fold change 1.81, p = 0.006) [30] were observed.…”

“…Some studies used the cells isolated from tissue that could be contaminated with immune cells present in the endometrium [30] while others used immunohistochemistry analysis of embedded tissue [31]. The selection of the control patients may be as well a source of variability in the different studies.…”

“…Moreover, an increase of enzyme expression has been reported during pregnancy, resulting in higher VD serum level necessary to meet the enhanced calcium requirements during this condition [24]. As previously mentioned, the mitochondrial and microsomal 25-hydroxylases (encoded by CYP27A1 and CYP2R1 , respectively), typically present in the liver, were found additionally in the human endometrium [30], where their expression is temporal and, specifically, higher in the secretory compared to proliferative phase of the cycle [30]. …”

“…On the other hand, a more recent immunostaining analysis of human tissues has found lower levels of nuclear VDR protein expression in 137 tumor samples compared with 55 samples from normal endometrium. Nonetheless, cytosolic VDR levels remained unvaried [30]. …”

Cytochrome P450 Vitamin D Hydroxylases in Inflammation and Cancer

“…A recent study showed that CYP2R1 (and CYP27B1) expression was increased in endometrial cancer, as an autocrine/paracrine defense mechanism (Bergada et al, 2014). Similarly, CYP2R1 expression was higher in oral squamous cell carcinomas (OSCCs), compared with the adjacent normal mucosa.…”