Thonberg H, Zhang S J, Tvrdik P, Jacobsson A, Nedergaard J
Wenner-Gren Institute, Arrhenius Laboratories F3, Stockholm University, Sweden.
J Biol Chem. 1994 Dec 30;269(52):33179-86.
In order to examine how norepinephrine stimulates proliferation and differentiation in brown fat cells, we have investigated the ability of brown fat cells to respond to norepinephrine stimulation with an increase in the expression of the proto-oncogene c-fos. Stimulation of brown fat precursor cells (isolated from young mice and grown for 4 days in culture) with norepinephrine led to a marked but transient (maximal approximately 30 min) induction of c-fos expression. The magnitude of this induction was similar in pre- and postconfluent cells. The norepinephrine effect could be blocked by both alpha 1- and beta-adrenergic antagonists. Forskolin had a small inductive ability, as had the selective alpha 1-agonist cirazoline, but with both together a high induction was obtained. The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) could in itself induce c-fos expression, but pretreatment with TPA did not abolish the ability of norepinephrine to induce c-fos expression, indicating that TPA-sensitive protein kinase C was not a primary mediator in this pathway. Also the Ca2+ ionophore A23187 had in itself an inductive ability, but A23187 in combination with forskolin led to a large increase in c-fos expression, indicating synergistic interaction between a cAMP pathway and a [Ca2+]i pathway. This interaction was not proximal, i.e. alpha 1 stimulation or increase in [Ca2+]i by A23187 did not augment forskolin-induced cAMP levels, and beta stimulation or forskolin did not affect [Ca2+]i levels; and it did not require protein synthesis. It was concluded that norepinephrine, in agreement with its fundamental role in the control of brown fat cell growth and development, was able to induce c-fos expression, that this induction was not exclusively linked to promotion of either proliferation or differentiation, and that the induction was mediated via a distal synergism between beta/cAMP and alpha 1/[Ca2+]i pathways, thus conferring to the alpha 1-adrenoreceptors on the cell a potentially significant role in the control of cell growth and development.
为了研究去甲肾上腺素如何刺激棕色脂肪细胞的增殖和分化，我们研究了棕色脂肪细胞对去甲肾上腺素刺激作出反应并增加原癌基因c-fos表达的能力。用去甲肾上腺素刺激棕色脂肪前体细胞（从小鼠幼崽中分离并在培养中生长4天）导致c-fos表达显著但短暂（最大约30分钟）的诱导。这种诱导的程度在汇合前和汇合后的细胞中相似。去甲肾上腺素的作用可被α1和β肾上腺素能拮抗剂阻断。福斯高林具有较小的诱导能力，选择性α1激动剂西拉唑啉也是如此，但两者一起使用可获得高诱导率。佛波酯12-O-十四酰佛波醇-13-乙酸酯（TPA）本身可诱导c-fos表达，但用TPA预处理并未消除去甲肾上腺素诱导c-fos表达的能力，这表明TPA敏感的蛋白激酶C不是该途径的主要介质。同样，Ca2+离子载体A23187本身也具有诱导能力，但A23187与福斯高林联合使用导致c-fos表达大幅增加，表明cAMP途径和[Ca2+]i途径之间存在协同相互作用。这种相互作用不是近端的，即α1刺激或A23187引起的[Ca2+]i增加不会增强福斯高林诱导的cAMP水平，β刺激或福斯高林也不会影响[Ca2+]i水平；并且它不需要蛋白质合成。得出的结论是，与去甲肾上腺素在棕色脂肪细胞生长和发育控制中的基本作用一致，可以诱导c-fos表达，这种诱导并非仅与增殖或分化的促进相关，并且该诱导是通过β/cAMP和αl/[Ca2+]i途径之间的远端协同作用介导的，从而赋予细胞上的α1肾上腺素能受体在细胞生长和发育控制中潜在的重要作用。
