Paillaud E, Costa S, Fages C, Plassat J L, Rochette-Egly C, Monville C, Tardy M
INSERM U-421, Medical Faculty, 8 rue General Sarrail, Creteil, France.
J Neurosci Res. 2002 Mar 1;67(5):670-9. doi: 10.1002/jnr.10110.
The molecular mechanisms underlying the heterogeneous effects of retinoic acid (RA) treatment on malignant glioma cells remain poorly understood. In this study, we present the first evidence of a functional role of the signal transduction factors (STATs) in RA-induced proliferation, in a human glioblastoma GL-15 cell line. We first observed that STAT-3 was constitutively activated and present in the GL-15 cell nuclei. We then showed that at low doses (0.01-1 microM) RA increased both the proliferation rate of GL-15 cells and the phosphotyrosine (PY) activation of STAT-3. This RA effect involved transcriptional processes and the transactivation of RA target genes, including RA receptors isoforms RARalpha2, -beta2, and -gamma2. At higher concentrations, however, RA (5-10 microM) inhibits GL-15 proliferation, induces apoptosis, and fails to activate STAT-3. An inhibitory effect on GL-15 proliferation was also observed with the synthetic retinoids CD-437 and CD-2325, two structurally related RARgamma agonists, which also fail to activate STAT-3. In addition, the phorbol ester PMA, an inducer of GL-15 differentiation, and staurosporine, a broad inhibitor of protein kinases, abrogate the stimulatory effects of RA at low concentrations. Together these observations suggest that, in GL-15 cells, activation of STAT-3 and cell proliferation share common mechanisms and that STAT transcription factors may be involved in a switch between proliferation, differentiation, and apoptosis. The proliferating effect observed at low doses of RA may be related to the failures in RA efficiency observed in clinical assays in relapsing malignant gliomas. Combining specific inhibitors of tyrosine kinases with RA might optimize the clinical outcome.
维甲酸（RA）治疗对恶性胶质瘤细胞产生异质性影响的分子机制仍知之甚少。在本研究中，我们首次证明了信号转导因子（STATs）在人胶质母细胞瘤GL - 15细胞系中RA诱导的增殖过程中发挥功能性作用。我们首先观察到STAT - 3在GL - 15细胞核中持续激活并存在。然后我们发现，低剂量（0.01 - 1 microM）的RA可提高GL - 15细胞的增殖率以及STAT - 3的磷酸酪氨酸（PY）激活水平。这种RA效应涉及转录过程以及RA靶基因的反式激活，包括RA受体亚型RARalpha2、-beta2和-gamma2。然而，在较高浓度下，RA（5 - 10 microM）会抑制GL - 15增殖、诱导凋亡，且无法激活STAT - 3。合成维甲酸CD - 437和CD - 2325（两种结构相关的RARgamma激动剂）对GL - 15增殖也有抑制作用，它们同样无法激活STAT - 3。此外，佛波酯PMA（一种GL - 15分化诱导剂）和星形孢菌素（一种广泛的蛋白激酶抑制剂）可消除低浓度RA的刺激作用。这些观察结果共同表明，在GL - 15细胞中，STAT - 3的激活与细胞增殖具有共同机制，并且STAT转录因子可能参与了增殖、分化和凋亡之间的转换。低剂量RA观察到的增殖效应可能与复发性恶性胶质瘤临床检测中RA疗效不佳有关。将酪氨酸激酶的特异性抑制剂与RA联合使用可能会优化临床结果。
