Hass R, Brach M, Kharbanda S, Giese G, Traub P, Kufe D
Laboratory of Clinical Pharmacology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
J Cell Physiol. 1991 Oct;149(1):125-31. doi: 10.1002/jcp.1041490116.
Previous studies have shown that treatment of human myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with induction of monocytic differentiation and expression of the c-jun and c-fos early response genes. The present work demonstrates that the glucocorticoid dexamethasone inhibits TPA-induced increases in c-jun and c-fos mRNA levels in U-937 leukemia cells. These findings were associated with a block in appearance of the monocytic phenotype, including inhibition of TPA-induced increases in lamin A, lamin C, and vimentin transcripts. Other studies have demonstrated that TPA-induced monocytic differentiation and expression of the c-jun and c-fos genes in myeloid leukemia cells are regulated by protein kinase C (PKC). The finding that dexamethasone has no effect on TPA-induced activation of PKC suggests that this glucocorticoid inhibits signals downstream or parallel to this enzyme. Nuclear run-on assays demonstrate that: (1) induction of c-jun and c-fos expression by TPA is regulated by transcriptional mechanisms, (2) TPA-induced expression of c-jun and c-fos does not require protein synthesis, and (3) TPA-induced expression of both genes is inhibited at the transcriptional level by dexamethasone. To further define the effects of dexamethasone at the molecular level, we prepared a series of deleted c-jun promoter fragments linked to the chloramphenicol acetyltransferase (CAT) gene. Increases in CAT activity during transient expression of these constructs in TPA-treated U-937 cells could be assigned to the region (-97 to -20) of the promoter that contains the AP-1 binding site. This induction of CAT activity was sensitive to dexamethasone. These findings suggest that dexamethasone down-regulates TPA-induced transcription of the c-jun gene during monocytic differentiation by inhibiting activation of the AP-1 site.
先前的研究表明，用12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA）处理人髓系白血病细胞与单核细胞分化的诱导以及c - jun和c - fos早期反应基因的表达有关。目前的研究表明，糖皮质激素地塞米松可抑制TPA诱导的U - 937白血病细胞中c - jun和c - fos mRNA水平的升高。这些发现与单核细胞表型的出现受阻有关，包括抑制TPA诱导的核纤层蛋白A、核纤层蛋白C和波形蛋白转录本的增加。其他研究表明，TPA诱导的髓系白血病细胞中的单核细胞分化以及c - jun和c - fos基因的表达受蛋白激酶C（PKC）调节。地塞米松对TPA诱导的PKC激活没有影响这一发现表明，这种糖皮质激素抑制该酶下游或与之平行的信号。核转录分析表明：（1）TPA诱导的c - jun和c - fos表达受转录机制调节，（2）TPA诱导的c - jun和c - fos表达不需要蛋白质合成，（3）地塞米松在转录水平抑制这两个基因的TPA诱导表达。为了在分子水平上进一步确定地塞米松的作用，我们制备了一系列与氯霉素乙酰转移酶（CAT）基因相连的缺失c - jun启动子片段。在TPA处理的U - 937细胞中瞬时表达这些构建体期间CAT活性的增加可归因于启动子的（-97至-20）区域，该区域包含AP - 1结合位点。这种CAT活性的诱导对地塞米松敏感。这些发现表明，地塞米松在单核细胞分化过程中通过抑制AP - 1位点的激活来下调TPA诱导的c - jun基因转录。
