Regulation of apoptosis by the retinoid AHPN

类维生素A 6-[3-（1-金刚烷基）-4-羟基苯基]-2-萘羧酸（AHPN）在多种癌细胞系中抑制细胞增殖并且是凋亡的有效诱导剂。为了更深入地了解AHPN诱导的生长停滞和凋亡的机制，我们开始使用人肺癌H460细胞通过cDNA阵列筛选来检查AHPN诱导的基因表达变化。该分析确定了几个AHPN诱导基因，包括立即早期基因Egr-1和Nur 77。AHPN能增加多种肿瘤细胞系中Egr-1和Nur 77 mRNA和蛋白的表达。这种诱导似乎在转录水平上受到调节，并且对AHPN是特异性的，因为RAR和RXR选择性类维生素A是无活性的。这些结果表明，诱导Egr-1和Nur 77的AHPN是独立的核维甲酸受体，并涉及一种新的机制。Bcl-2的过表达，抑制AHPN诱导的细胞凋亡，但不生长停滞在人类T细胞淋巴瘤Molt-4细胞，并没有阻止立即早期基因表达的诱导。AHPN处理H460细胞可诱导p38 MAP-激酶的激活，但不诱导ERK 1/2信号通路的激活。然而，通过PD 98059抑制ERK 1/2信号通路阻断Egr-1和Nur 77 mRNA的诱导，而p38 MAPK抑制剂PD 169316几乎没有影响。显性负性ERK 1的表达完全消除了Egr-1 mRNA的增加，并降低了AHPN的生长抑制作用。我们的结果表明，AHPN对H460中Egr-1的诱导需要激活的ERK 1/2，并且不依赖于p38的激活。Egr-1与其他几种生长抑制蛋白一起，可能参与AHPN诱导的细胞生长抑制。

The retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (AHPN) inhibits cell proliferation and is an effective inducer of apoptosis in a variety of carcinoma cell lines. In order to obtain greater insight into the mechanism of AHPN-induced growth arrest and apoptosis, we began to examine AHPN-induced changes in gene expression by cDNA array screening using human lung carcinoma H460 cells. This analysis identified several AHPN-inducible genes, including the immediate-early genes Egr-1 and Nur77. AHPN was able to increase Egr-1 and Nur77 mRNA expression and protein in a variety of carcinoma cell lines. This induction appeared to be regulated at the transcriptional level and was specific for AHPN since an RAR- and an RXR-selective retinoid were inactive. These results suggest that the induction of Egr-1 and Nur77 by AHPN is independent of nuclear retinoid receptors and involves a novel mechanism. Overexpression of Bcl-2, which inhibits AHPN-induced apoptosis but not growth arrest in human T cell lymphoma Molt-4 cells, did not block the induction of immediate-early gene expression. Treatment of H460 cells with AHPN induced activation of the p38 MAP-kinase but not the ERK1/2 signaling pathway. However, inhibition of the ERK1/2 signaling pathway by PD98059 blocked the induction of Egr-1 and Nur77 mRNA while the p38 MAPK inhibitor PD169316 had little effect. Expression of a dominant-negative ERK1 completely abolished the increase in Egr-1 mRNA and reduced growth inhibition by AHPN. Our results suggest that the induction of Egr-1 in H460 by AHPN requires active ERK1/2 and is independent of p38 activation. Egr-1, in cooperation with several other growth-suppressor proteins, is likely involved in AHPN-induced inhibition of cell growth.