Serotonin Suppresses β-Casein Expression <i>via</i> Inhibition of the Signal Transducer and Activator of Transcription 5 (STAT5) Protein Phosphorylation in Human Mammary Epithelial Cells MCF-12A

Abstract

Serotonin (5-hydroxytryptamine; 5-HT) has an important physiological role in controlling lactation, namely, milk volume homeostasis, within mammary glands. The objectives of this study were to evaluate whether exogenous 5-HT can suppress β-casein expression, a differentiation marker, produced in human mammary epithelial cells, and to determine whether 5-HT can attenuate β-casein signaling via the prolactin (PRL) receptor (PRLr) and Janus kinase 2/signal transducer and activator of transcription 5 (STAT5) pathway. PRL treatment increased the mRNA level of β-casein in the MCF-12A human mammary epithelial cell line, and the highest level occurred at days 7 and 14 of culture. In contrast, PRLr expression was not affected significantly by PRL treatment. PRL treatment in MCF-12A cells increased levels of β-casein and phosphorylated STAT5 (pSTAT5) proteins in a concentration-dependent manner, with a slight increase of STAT5 protein. β-Casein expression was inhibited by 0.1 mM 5-HT in a time-dependent manner. Additionally, treatment with 0.1 mM 5-HT for 72 h decreased protein levels of β-casein and pSTAT5, with a slight decrease in STAT5 levels. These results suggest that exogenous 5-HT can inhibit STAT5 phosphorylation, resulting in a decrease in β-Casein expression. In conclusion, we showed that exogenous 5-HT decreased β-casein expression in MCF-12A human mammary epithelial cells, and that 5-HT was responsible for inhibiting phosphorylation of STAT5, resulting in a decline in lactational function.

Serotonin Regulates β-Casein Expression <i>via</i> 5-HT₇ Receptors in Human Mammary Epithelial MCF-12A Cells

“…Treatment with 100 µM 5-HT for 72 h inhibited β-casein expression, and this inhibition was associated with the suppression of STAT5 phosphorylation. 15) In this study, we found that 30 µM 5-HT inhibited β-casein mRNA expression in a time-dependent manner (Fig. 1A).…”

“…[12][13][14] In our previous study, PRL treatment induced β-casein expression in the human mammary epithelial cell line MCF-12A via activation of the Jak2/STAT5 pathway. We also showed that 5-HT treatment decreased β-casein levels, with a concomitant reduction in STAT5 phosphorylation (pSTAT5), 15) suggesting that suppression of β-casein by 5-HT was associated with reduced STAT5 phosphorylation. These results implied that endogenous 5-HT in MCF-12A cells may be secreted and signal in an autocrine and/or paracrine manner in MCF-12A cells.…”

“…15) Briefly, the cells were seeded at a density of 1×10 5 cells/cm 2 on dishes coated with Matrigel ® (BD Biosciences, MA, U.S.A.), and were cultured in growth medium (GM) consisting of DMEM : F12 (1 : 1, Invitrogen, CA, U.S.A.) supplemented with 10 µg/mL human insulin (Sigma-Aldrich, MO, U.S.A.), 0.5 µg/mL hydrocortisone (Sigma-Aldrich), 20 ng/mL human recombinant epithelial growth factor (hEGF; BD Biosciences), 5% horse serum (Invitrogen, CA, U.S.A.), 100 IU/mL penicillin, and 100 µg/mL streptomycin (SigmaAldrich). Unless otherwise stated, the GM was changed to differentiation medium (DM), modified by the addition of 0.1 µg/ mL PRL and the removal of hEGF, 24 h after cell seeding for 7 d. For treatment with 5-HT and/or 5-HTR antagonists, no horse serum was added to the DM.…”

“…15) Cells were grown for 7 d (in GM for 1 d and in DM for 6 d) after seeding, and then cultured in DM containing 30 µM 5-HT for 24 to 96 h (Fig. 1A).…”

STAT5a/b contribute to sex bias in vascular disease: A neuroendocrine perspective

“…102 Additionally, it is already known that PY-STAT5 signaling in the hypothalamus is involved in regulating appetite and sex-biased changes in body weight. 103 It has been shown already that 5-HT suppresses STAT5 expression and PY-STAT5 activation, 104 and 5-HT-receptor and dopaminergic D1, D2 receptor antagonists also inhibit PY-STAT5 activation (e.g., pimozide). 105,106 We suggest that consideration of mechanisms in such models also include the central effects of 5-HT at the level of the hypothalamus and the arcuate nucleus, and sex-specific changes in the patterns of GH secretion and STAT5 activation.…”