AG and UAG induce β-casein expression via activation of ERK1/2 and AKT pathways

Abstract

The ghrelin peptides were found to circulate in two major forms: acylated ghrelin (AG) and unacylated ghrelin (UAG). Previous studies showed that AG regulates β-casein (CSN2) expression in mammary epithelial cells. However, little is known about the mechanisms by which AG regulates CSN2 gene and protein expression. Evidence suggests that UAG has biological activity through GHSR1a-independent mechanisms. Here, we investigated the possible GHSR1a-mediated effect of UAG on the expression of CSN2 in primary bovine mammary epithelial cells (pbMECs) isolated from lactating cow. We found that both AG and UAG increase the expression of CSN2 in a dose-dependent manner in pbMECs in comparison with the control group. Increased expression of CSN2 was blocked by [D-Lys3]-GHRP-6 (an antagonist of the GHSR1a) and NF449 (a Gs-α subunit inhibitor) in pbMECs. In addition, both AG and UAG activated AKT/protein kinase B (AKT) and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways, whereas [D-Lys3]-GHRP-6 and NF449 inhibited the phosphorylation of AKT and ERK1/2 in pbMECs respectively. Blockade of ERK1/2 and AKT signaling pathways prevented the expression of CSN2 induced by AG or UAG. Finally, we found that both AG and UAG cause cell proliferation through identical signaling pathways. Taken together, these results demonstrate that both AG and UAG act on ERK1/2 and AKT signaling pathways to facilitate the expression of CSN2 in a GHSR1a-dependent manner.

Carica papaya leaf ethanol extract effect on milk volume, β-casein gene (Csn2) expression, β-casein levels, and milk total protein levels

“…A study by Li et al showed that β-casein gene expression can be regulated by acylated ghrelin and unacylated ghrelin in a dose-dependent manner in primary bovine mammary epithelial cells 47…”

Negative regulation of αS1-casein (CSN1S1) improves β-casein content and reduces allergy potential in goat milk

“…Ghrelin peptides and methionyl-methionine dipeptides increase CSN2 expression and β-casein synthesis in BMEC by activating JAK2/STAT5 and mTOR signaling (Li et al, 2016;Wang et al, 2018). In fact, both of these intracellular signaling pathways are known to participate in the control of bovine milk protein synthesis (β-casein and κ-casein) as it relates to lysine and leucine supply (Lin et al, 2018;Zhao et al, 2019) or the supply of glucose and amino acids (Zhang et al, 2018b).…”

Kisspeptin-10 Induces β-Casein Synthesis via GPR54 and Its Downstream Signaling Pathways in Bovine Mammary Epithelial Cells

“…At present, we have found that Kp-10 can promote CSN2 synthesis by activating GPR54.However, the exact molecular mechanism remains unclear, and so the next step is to detect the changes in downstream signals in the process. The CSN2 synthesis process is likely to include several participating signaling pathways, including ERK1/2, AKT, STAT, mTOR [ 6 , 19 , 20 , 40 , 41 ]. In addition, Kp-10 plays the role of an anti-metastasis agent via β-arrestin2/ERK by binding with GPR54 in human breast cancer cells [ 8 ].…”

“…According to the reports, growth hormone (GH) in calves contributes to the growth and development of the mammary gland and thereafter to increase milk production [ 4 , 5 ]. In addition, the protein hormones ghrelin (AG) and unacylated ghrelin (UAG) can induce the synthesis of milk protein CSN2 in bovine mammary epithelial cells [ 6 ]. Therefore, the protein hormones that regulate the milk protein CSN2 may play an important role in improving the quality of milk in production.…”

“…Some studies have shown that the PI3K/AKT pathway is involved in lipid lactose milk protein synthesis, and furthermore, that there is a direct link between PI3K/AKT and STAT5 [ 25 , 26 ]. Moreover, ERK1/2 and AKT are also both involved in the process of CSN2 synthesis [ 6 ]. Among them, thePI3K/AKT and ERK1/2 pathways are both activated in mammary epithelial cell (MEC) number and their activity affected by IGF-I [ 27 ].…”