J Anim Sci. 2017 Dec;95(12):5365-5377. doi: 10.2527/jas2017.1877.
Fibroblast growth factor (FGF) signaling plays essential roles in tissue development and homeostasis. Accumulating evidence reveals that fibroblast growth factor 2 (FGF2) regulates ductal elongation, which requires cell proliferation and epithelial expansion in the mammary gland. However, the function and mechanisms by which FGF2 controls functionality of epithelial cells is less well defined. Here, we demonstrate the functional effects of FGF2 on bovine mammary epithelial (MAC-T) cells and the intracellular signaling mechanisms for these FGF2-induced actions. The current results show that treatment of MAC-T cells with a recombinant FGF2 induced cell proliferation and cell-cycle progression with increased expression of proliferating cell nuclear antigen and cyclin D1. Moreover, FGF2 increased phosphorylation of serine/threonine protein kinase (protein kinase B [AKT]), extracellular signal-regulated kinases 1 and 2 (ERK1/2), Jun N-terminal kinase (JNK), 70 kDa ribosomal S6 kinase (P70S6K), 90 kDa ribosomal S6 kinase (P90S6K), ribosomal protein S6 (S6), and cyclin D1 proteins. These FGF2-induced activations of signaling pathway proteins were inhibited by blocking AKT, ERK1/2, or JNK phosphorylation. The effect of FGF2 to stimulate MAC-T cell proliferation was mediated by activation of FGF receptors (FGFR) and AKT, ERK1/2, and JNK mitogen-activated protein kinase pathways in response to FGF2 stimulation. Furthermore, expression and activation of endoplasmic reticulum (ER) stress-related factors and ER stress-induced MAC-T cell death was reduced by FGF2. Together, these results suggest that the FGF2-FGFR-intracellular signaling cascades may contribute to maintaining and/or increasing numbers of mammary epithelial cells by inducing proliferation of mammary epithelial cells and by protecting cells from ER stress responses. Therefore, this study provides evidence that FGF2 signaling is a positive factor for mammary gland remodeling and for increasing persistency of milk production.
成纤维细胞生长因子（FGF）信号在组织发育和内稳态中发挥着重要作用。越来越多的证据表明，成纤维细胞生长因子 2（FGF2）调节导管伸长，这需要乳腺中的细胞增殖和上皮扩张。然而，FGF2 控制上皮细胞功能的作用和机制尚未得到很好的定义。在这里，我们展示了 FGF2 对牛乳腺上皮（MAC-T）细胞的功能影响，以及这些 FGF2 诱导作用的细胞内信号机制。目前的结果表明，用重组 FGF2 处理 MAC-T 细胞会诱导细胞增殖和细胞周期进程，导致增殖细胞核抗原和细胞周期蛋白 D1 的表达增加。此外，FGF2 增加了丝氨酸/苏氨酸蛋白激酶（蛋白激酶 B [AKT]）、细胞外信号调节激酶 1 和 2（ERK1/2）、Jun N-末端激酶（JNK）、70 kDa 核糖体 S6 激酶（P70S6K）、90 kDa 核糖体 S6 激酶（P90S6K）、核糖体蛋白 S6（S6）和细胞周期蛋白 D1 蛋白的磷酸化。这些 FGF2 诱导的信号通路蛋白的激活被阻断 AKT、ERK1/2 或 JNK 磷酸化所抑制。FGF2 刺激 MAC-T 细胞增殖的作用是通过 FGF2 刺激后激活 FGF 受体（FGFR）和 AKT、ERK1/2 和 JNK 丝裂原激活蛋白激酶途径来介导的。此外，FGF2 还降低了内质网（ER）应激相关因子的表达和激活，以及 ER 应激诱导的 MAC-T 细胞死亡。总之，这些结果表明，FGF2-FGFR-细胞内信号级联可能通过诱导乳腺上皮细胞增殖和保护细胞免受 ER 应激反应来维持和/或增加乳腺上皮细胞的数量。因此，本研究为 FGF2 信号是乳腺重塑和增加牛奶产量持续性的积极因素提供了证据。
