Autocrine metabolism of vitamin D in normal and malignant breast tissue.
OBJECTIVE
Vitamin D seems to exert a protective effect against common cancers, although this does not correlate with circulating levels of active 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], indicating a more localized activation of vitamin D. The aim of this study was to investigate the significance of this in breast cancer.


METHODS
Quantitative reverse transcription-PCR analysis of mRNA expression was carried out for the vitamin D-activating enzyme 1alpha-hydroxylase, the catabolic enzyme 24-hydroxylase, and the vitamin D receptor in 41 tumors and paired nonneoplastic tissue as well as breast cancer cell lines. Immunohistochemistry was used to assess 1alpha-hydroxylase protein expression, and enzyme assays were used to quantify vitamin D metabolism.


RESULTS
Expression of mRNA for 1alpha-hydroxylase (27-fold; P < 5 x 10(-11)), vitamin D receptor (7-fold; P < 1.5 x 10(-8)), and 24-hydroxylase (4-fold; P < 0.02) was higher in breast tumors. 1alpha-Hydroxylase enzyme activity was also higher in tumors (44.3 +/- 11.4 versus 12.4 +/- 4.8 fmol/h/mg protein in nonneoplastic tissue; P < 0.05). However, production of inactive 1,24,25-trihydroxyvitamin D3 was also significantly higher in tumors (84.8 +/- 11.7 versus 33.6 +/- 8.5 fmol/h/mg protein; P < 0.01). Antisense inhibition of 24-hydroxylase in vitro increased antiproliferative responses to 1,25(OH)2D3.


CONCLUSIONS
These data indicate that the vitamin D-activating enzyme 1alpha-hydroxylase is up-regulated in breast tumors. However, dysregulated expression of 24-hydroxylase seems to abrogate the effects of local 1,25(OH)2D3 production in tumors by catalyzing catabolism to less active vitamin D metabolites. The enzymes involved in autocrine metabolism of vitamin D in breast tissue may therefore provide important targets for both the prevention and treatment of breast cancer.
Townsend
Kelly
K
Division of Medical Sciences, Institute of Biomedical Research, Endocrinology and Metabolism, University of Birmingham, Birmingham, United Kingdom.
Banwell
Claire M
CM
Guy
Michelle
M
Colston
Kay W
KW
Mansi
Janine L
JL
Stewart
Paul M
PM
Campbell
Moray J
MJ
Hewison
Martin
M
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001940:Breast / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002112:Calcifediol / Q000378:metabolism* / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D008875:Middle Aged; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism; D065668:Vitamin D3 24-Hydroxylase
D016376:Oligonucleotides, Antisense; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D000255:Adenosine Triphosphate; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol; D002112:Calcifediol