Low concentrations mono-butyl phthalate stimulates steroidogenesis by facilitating steroidogenic acute regulatory protein expression in mouse Leydig tumor cells (MLTC-1).
Di-n-butyl phthalate (DBP) is one of the most dominant phthalate esters and is widely distributed environmental contaminant. Although previous studies have demonstrated that DBP led to a variety of male reproductive abnormalities similar to those caused by androgen receptor antagonists, DBP and its active metabolite, mono-butyl phthalate (MBP), have been demonstrated no affinity for the androgen receptor, but rather exert anti-androgenic effect by altering testosterone biosynthesis. Furthermore, all these results were obtained from very high administrations of DBP or MBP. The purpose of this study was to determine the onset and the site of action of relatively low concentration of MBP on steroidogenesis in vitro. The mouse Leydig tumor cells (MLTC-1) was employed as a cellular model to investigate the effect of MBP on steroidogenesis. Various concentrations of MBP (1, 10, 100 and 1000nmol/l) and its solvent dimethyl sulfoxide (DMSO) were added to the medium for 24h followed by stimulation of some compounds such as human chorionic gonadotrophin (hCG), cholera toxin (CT), forskolin, cAMP analog 8-Br-cAMP, 22(R)-hydroxycholesterol (22R-HC) and pregnenolone. Progesterone in the medium and amounts of intracellular cAMP were measured by RIA. Expression of steroidogenic acute regulatory protein (StAR) was monitored by real-time PCR and Western blotting. The results revealed that the increases of progesterone production in the presence of hCG, CT, forskolin and 8-Br-cAMP were augmented by MBP. In contrast, the levels of intracellular cAMP exhibited no statistical significance when MLTC-1 cells were treated as above. These results implied that the site in the steroid biosynthesis pathway affected by MBP occurs after PKA activation in MLTC-1 cells. Moreover, supplementing the medium with 22R-HC and pregnenolone as progesterone precursors for P450 side chain cleavage enzyme (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD), respectively, resulted in no rise in progesterone production, making clear that MBP did not influence the P450scc and 3beta-HSD but on the rate-limiting step, cholesterol transportation into mitochondria. In fact, the above results were confirmed by the upgraded StAR expression in MBP-treated cells. These data support that MBP promotes steroid hormone production by facilitating StAR expression in MLTC-1 cells.
Wang
Yubang
Y
Key Laboratory of Reproductive Medicine of Jiangsu Province, Institute of Toxicology, Nanjing Medical University, Nanjing 210029, PR China.
Song
Ling
L
Hong
Xia
X
Cui
Lunbiao
L
Zhang
Zhengdong
Z
Xiao
Hang
H
Zhou
Jianwei
J
Wang
Xinru
X
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D059002:Androgen Receptor Antagonists; D000818:Animals; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D003993:Dibutyl Phthalate / Q000008:administration & dosage / Q000494:pharmacology*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D007984:Leydig Cell Tumor / Q000378:metabolism*; D008297:Male; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011374:Progesterone / Q000096:biosynthesis*; D013268:Stimulation, Chemical; D013739:Testosterone / Q000096:biosynthesis*; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000502:physiology; D000098682:Steroidogenic Acute Regulatory Protein
D059002:Androgen Receptor Antagonists; D010750:Phosphoproteins; D000098682:Steroidogenic Acute Regulatory Protein; D003993:Dibutyl Phthalate; D013739:Testosterone; D011374:Progesterone; D000242:Cyclic AMP; D015067:17-Hydroxysteroid Dehydrogenases; C044256:3 (or 17)-beta-hydroxysteroid dehydrogenase; D002786:Cholesterol Side-Chain Cleavage Enzyme; D004121:Dimethyl Sulfoxide