Low-dose bisphenol A activates the ERK signaling pathway and attenuates steroidogenic gene expression in human placental cells.

Bisphenol A (BPA) is an industrial material used for many plastic products and is considered an endocrine disruptor. BPA can be released into the environment and can spread through the food chain. It is well known that BPA exposure leads to lesions, especially in the reproductive system. According to previous studies, BPA reduces newborn numbers in pregnant mice and affects placentation. The placenta is a special endocrine organ during pregnancy. It secretes important hormones, such as progesterone and estrogen, to maintain gestation. In steroid hormone synthesis, two specific enzymes are important: P450scc (CYP11A1) converts cholesterol to pregnenolone and aromatase (CYP19) induces androgen conversion to estrogen.To determine the effects of a low dose of BPA on hormone synthesis in the placenta, we used JEG-3 cells as a model. We found that the steroidogenic genes CYP11A1 and CYP19 were downregulated in human tissues by detectable concentrations of BPA (1-1000 nM), which do not affect cell viability. Furthermore, we demonstrated that BPA influenced the ERK signaling pathway and resulted in hormone reductions. An analysis of trophoblasts in primary culture from a term human placenta showed the same phenomena. Our data demonstrate that treatment with a low dose of BPA does not affect human placental cell survival, but decreases hormone production via to the downregulation of steroidogenic genes and ERK signaling pathway changes.

Bisphenol A disrupts steroidogenesis and induces a sex hormone imbalance through c-Jun phosphorylation in Leydig cells.

Bisphenol A (BPA) is a well-known endocrine disrupting chemical (EDC) that is used to manufacture plastic consumer products. It is well known that exposure to BPA can induce defects in gonad development and negatively influences reproductive function in both males and females. In this study, we assessed the effects of BPA on hormone production in Leydig cells, which secrete hormones in the testes and support male fertility. We examined two steroidogenic enzymes, CYP11A1 and CYP19 that involved in sex hormone synthesis in mouse MA-10 Leydig cells. We found that BPA activated CYP gene in both mRNA and protein levels then resulted in alteration of the normal sex hormone ratio. Furthermore, we found that BPA induced c-Jun phosphorylation and contributed to CYP gene expression. Similar results were observed in an animal study. In conclusion, BPA disrupts the hormone environment in testis via steroidogenic gene activation through the JNK/c-Jun signaling pathway.

Low-dose Bisphenol A Activates Cyp11a1 Gene Expression and Corticosterone Secretion in Adrenal Gland via the JNK Signaling Pathway.

Certain commonly used compounds that interfere with the functions of the endocrine system are classified as endocrine-disrupting chemicals (EDCs). Bisphenol A (BPA) is an EDC that is widely used in food containers. BPA levels in human sera are commonly observed to be approximately 1-100 nM. Compared with the effects of BPA on the gonads, its effects on the adrenal gland are poorly understood. To investigate the influence of BPA on steroidogenesis, we examined the activity of the steroidogenic gene Cyp11a1 and its regulatory pathways in mouse Y1 adrenal cortex cells. Treatment with BPA at < 100 µM did not cause cell death. However, increased promoter activity and protein expression of Cyp11a1 were induced by low doses of BPA (10-1000 nM). Moreover, BPA induced c-Jun phosphorylation, and a specific inhibitor of c-Jun N-terminal kinase (JNK) significantly suppressed BPA-induced steroidogenesis. Thus, treatment of adrenal cells with low doses of BPA activated Cyp11a1 and increased corticosterone production through the JNK/c-Jun signaling pathway. Identical results were observed in rats after BPA injection. The abnormal induction of hormone synthesis by BPA in the adrenal gland might be linked to human metabolic defects and neuropsychiatric disorders.

Death-associated protein 6 (Daxx) mediates cAMP-dependent stimulation of Cyp11a1 (P450scc) transcription.

SF-1 is a key transcription factor for all steroidogenic genes. It up-regulates the expression of the steroidogenic Cyp11a1 gene in the adrenal in a pathway stimulated by cAMP through HIPK3-mediated JNK/c-Jun phosphorylation. In the present study, we have investigated the factors mediating cAMP-dependent HIPK3 action to potentiate the activity of SF-1 for Cyp11a1 transcription in mouse adrenocortical Y1 cells. We found Daxx, a HIPK kinase substrate in the apoptosis pathway, was phosphorylated by HIPK3 at Ser-669 in response to cAMP stimulation. Daxx participated in SF-1-dependent Cyp11a1 expression as shown by experiments involving both overexpression and down-regulation via a dominant negative Daxx mutant. The S669A mutant of Daxx, which could not be phosphorylated by HIPK3, lost the ability to potentiate SF-1 activity for Cyp11a1 expression. The enhancement of SF-1 activity by Daxx required JNK and c-Jun phosphorylation. Thus, Daxx functioned as a signal transducer linking cAMP-stimulated HIPK3 activity with JNK/c-Jun phosphorylation and SF-1-dependent Cyp11a1 transcription for steroid synthesis.

Transcriptional regulation of human CYP11A1 in gonads and adrenals.

The CYP11A1 gene encodes the cholesterol side-chain cleavage enzyme, also termed cytochrome P450scc, which catalyzes the conversion of cholesterol to pregnenolone in the first step of steroid biosynthesis in mitochondria. The adrenal- and gonad-selective, hormonally and developmentally regulated expression of CYP11A1 is principally driven by its 2.3 kb promoter. Multiple trans-acting factors like SF-1, Sp1, AP-2, TReP-132, LBP-1b, LBP-9, AP-1, NF-1, and Ets control CYP11A1 transcription either through DNA-protein interaction with their specific cis-acting elements or through protein-protein interaction between each other, wherein SF-1 plays a central role in adrenals and testes. In addition to binding with its proximal and upstream motifs, SF-1 also physically interacts with TFIIB, CBP/p300, TReP-132, and c-Jun/AP-1 to specifically transmit the regulatory signals of cAMP. Other factors like Sp1 family members, AP-2, and LBP-1b/LBP-9 may be other factors that play a role in CYP11A1 transcription, particularly in placental cells. The TATA sequence could also contribute to tissue-specificity and hormonal regulation of CYP11A1 transcription. This article reviews recent studies focusing on adrenals and gonads.

Cyclic AMP stimulates SF-1-dependent CYP11A1 expression through homeodomain-interacting protein kinase 3-mediated Jun N-terminal kinase and c-Jun phosphorylation.

Steroids are synthesized in adrenal glands and gonads under the control of pituitary peptides. These peptides bind to cell surface receptors to activate the cyclic AMP (cAMP) signaling pathway leading to an increase of steroidogenic gene expression. Exactly how cAMP activates steroidogenic gene expression is not clear, except for the knowledge that transcription factor SF-1 plays a key role. Investigating the factors participating in SF-1 action, we found that c-Jun and homeodomain-interacting protein kinase 3 (HIPK3) were required for basal and cAMP-stimulated expression of one major steroidogenic gene, CYP11A1. HIPK3 enhanced SF-1 activity, and c-Jun was required for the functional interaction of HIPK3 with SF-1. Furthermore, after cAMP stimulation, both c-Jun and Jun N-terminal kinase (JNK) were phosphorylated through HIPK3. These phosphorylations were important for SF-1 activity and CYP11A1 expression. Thus, we have defined HIPK3-mediated JNK activity and c-Jun phosphorylation as important events that increase SF-1 activity for CYP11A1 transcription in response to cAMP. This finding has linked three common factors, HIPK3, JNK, and c-Jun, to the cAMP signaling pathway leading to increased steroidogenic gene expression.

Tuning up or down the UV-induced apoptosis in Chinese hamster ovary cells with cell cycle inhibitors.

Exposure to UVC induces apoptosis in Chinese hamster ovary (CHO.K1) cells. While studying the underlying mechanism, we found that a variety of cell cycle inhibitors, including colcemid, hydroxyurea and mimosine, enhance the UV-induced apoptosis in these cells. Such enhancement was not dependent on the cell cycle progression nor was it related to the difference in UV sensitivity at different phases of the cell cycle. The expression of p21(waf1/cip1), a general cyclin-dependent kinase (CDK) inhibitor, was deficient in CHO.K1 cells. Ectopic overexpression of the human p21 markedly increased the survival rates of the UV-irradiated cells in the presence of colcemid. In addition, roscovitine, a small-molecule inhibitor of CDK, also inhibited the UV-induced apoptosis. These observations suggest that deregulation of CDK activity may be critical in the UV-induced apoptosis in CHO.K1 cells.