Stefana B, Ray D W, Melmed S
Division of Endocrinology and Metabolism, Cedars-Sinai Research Institute, UCLA School of Medicine 90048, USA.
Proc Natl Acad Sci U S A. 1996 Oct 29;93(22):12502-6. doi: 10.1073/pnas.93.22.12502.
Leukemia inhibitory factor (LIF) promotes differentiated cell function in several systems. We recently reported LIF and LIF receptor expression in human fetal pituitary corticotrophs in vivo and demonstrated LIF stimulation of adrenocorticotrophin (ACTH) transcription in vitro, suggesting a role for LIF in corticotroph development. We therefore assessed the action of LIF on proliferating murine corticotroph cells (AtT20). LIF impairs proliferation of AtT20 cells (25% reduction versus control, P < 0.03), while simultaneously enhancing ACTH secretion (2-fold, P < 0.001) and augmenting ACTH responsiveness to corticotrophin-releasing hormone (CRH) action (4-fold, P < 0.001). This attenuation of cell growth is due to a block of cell cycle progression from G1 into S phase, as measured by flow cytometric analysis (24 +/- 0.8 versus 11.57 +/- 1.5, P < 0.001). Using bromodeoxyuridine incorporation assays, loss of cells in S phase was confirmed (25 +/- 0.08 to 9.4 +/- 1.4, P < 0.008). In contrast, CRH induced the G2/M phase (3.6 +/- 0.2 to 15.4 +/- 3, P < 0.001). This effect was blunted by LIF (P < 0.001 versus CRH alone). Cyclin A mRNA levels, which decline in S phase, were stimulated 3.5-fold by LIF and markedly suppressed by CRH. These results indicate a LIF-induced cell cycle block occurring at G1/S in corticotroph cells. Thus, LIF reduces proliferation, enhances ACTH secretion, and potentiates effects of CRH on ACTH secretion while blocking effects of CRH on the cell cycle. Responses of these three markers of differentiated corticotroph function indicate LIF to be a differentiation factor for pituitary corticotroph cells by preferential phenotypic switching from proliferative to synthetic.
白血病抑制因子（LIF）在多个系统中促进分化细胞的功能。我们最近报道了LIF及其受体在人胎儿垂体促肾上腺皮质激素细胞中的体内表达，并在体外证实了LIF对促肾上腺皮质激素（ACTH）转录的刺激作用，提示LIF在促肾上腺皮质激素细胞发育中发挥作用。因此，我们评估了LIF对增殖的小鼠促肾上腺皮质激素细胞（AtT20）的作用。LIF抑制AtT20细胞的增殖（与对照组相比减少25%，P<0.03），同时增强ACTH分泌（增加2倍，P<0.001）并增强ACTH对促肾上腺皮质激素释放激素（CRH）作用的反应性（增加4倍，P<0.001）。细胞生长的这种减弱是由于细胞周期从G1期进入S期受阻，通过流式细胞术分析测量（24±0.8对11.57±1.5，P<0.001）。使用溴脱氧尿苷掺入试验，证实了S期细胞的减少（25±0.08至9.4±1.4，P<0.008）。相反，CRH诱导G2/M期（3.6±0.2至15.4±3，P<0.001）。LIF使这种效应减弱（与单独使用CRH相比，P<0.001）。细胞周期蛋白A mRNA水平在S期下降，LIF使其升高3.5倍，而CRH则明显抑制它。这些结果表明LIF诱导促肾上腺皮质激素细胞在G1/S期出现细胞周期阻滞。因此，LIF减少增殖，增强ACTH分泌，并增强CRH对ACTH分泌的作用，同时阻断CRH对细胞周期的作用。这三种分化的促肾上腺皮质激素细胞功能标志物的反应表明，LIF通过从增殖型到合成型的优先表型转换，是垂体促肾上腺皮质激素细胞的分化因子。
