Inhibition of Protein Kinase CK2 Reduces Cyp24a1 Expression and Enhances 1,25-Dihydroxyvitamin D3 Antitumor Activity in Human Prostate Cancer Cells

Abstract

Vitamin D has broad range of physiological functions and anti-tumor effects. 24-hydroxylase, encoded by the CYP24A1 gene, is the key enzyme for degrading many forms of vitamin D including the most active form, 1,25D3. Inhibition of CYP24A1 enhances 1,25D3 anti-tumor activity. In order to isolate regulators of CYP24A1 expression in prostate cancer cells, we established a stable prostate cancer cell line PC3 with CYP24A1 promoter driving luciferase expression to screen a small molecular library for compounds that inhibit CYP24A1 promoter activity. From this screening, we identified, 4,5,6,7-tetrabromobenzimidazole (TBBz), a protein kinase CK2 selective inhibitor as a disruptor of CYP24A1 promoter activity. We show that TBBz inhibits CYP24A1 promoter activity induced by 1,25D3 in prostate cancer cells. In addition, TBBz downregulates endogenous CYP24A1 mRNA level in TBBz treated PC3 cells. Furthermore, siRNA-mediated CK2 knockdown reduces 1,25D3 induced CYP24A1 mRNA expression in PC3 cells. These results suggest that CK2 contributes to 1,25D3 mediated target gene expression. Lastly, inhibition of CK2 by TBBz or CK2 siRNA significantly enhanced 1,25D3 mediated anti-proliferative effect in vitro and in vivo in a xenograft model. In summary, our findings reveal that protein kinase CK2 is involved in the regulation of CYP24A1 expression by 1,25D3 and CK2 inhibitor enhances 1,25D3 mediated anti-tumor effect.

Increased CYP24A1 expression is associated with BRAFV600E mutation and advanced stages in papillary thyroid carcinoma

“…23 Multiple mechanisms are involved in its overexpression: for example, gene amplification in breast and colon cancers, 23,24 down-regulation of miR-125b in breast cancer 25 and activation of protein kinase CK2 in human prostate cancer. 26 miR-125b regulates CYP24A1 expression post-transcriptionally, and its expression is inversely correlated with CYP24A1 protein level. 25 Interestingly, miR-125b is down-regulated in anaplastic thyroid carcinoma.…”

“…Overexpression of CYP24A1 has been reported in many cancers and can lead to abrogation of growth control mediated by vitamin D. It has thus been proposed as a candidate oncogene . Multiple mechanisms are involved in its overexpression: for example, gene amplification in breast and colon cancers, down‐regulation of miR‐125b in breast cancer and activation of protein kinase CK2 in human prostate cancer . miR‐125b regulates CYP24A1 expression post‐transcriptionally, and its expression is inversely correlated with CYP24A1 protein level .…”

Role of Vitamin D and Risk of prostate cancer

“…Chronic inflammation promotes metastases and progression to castration-resistant prostate cancer [11,12]. CRP could predict tumor aggressiveness and potential treatment efficacy in patients with prostate cancer [13]. According to an early report, CRP is an independent prognostic factor for overall survival of patients with castration-resistant prostate cancer treated with docetaxel [14].…”

Association among plasma 1,25(OH)2D, ratio of 1,25(OH)2D to 25(OH)D, and prostate cancer aggressiveness

“…In vivo, dietary vitamin D or calcitriol supplementation reduced prostate cancer xenograft growth and increased 1,25(OH) 2 D serum levels . In another study, disruption of CYP24A1 activity increased 1,25(OH) 2 D levels and reduced prostate cancer growth in vitro and in vivo . However, the mechanism of action of 1,25(OH) 2 D was not defined well in these studies.…”