Regulation of apoptosis by the retinoid AHPN

类维甲酸6-[3-（1-金刚烷基）-4-羟基苯基]-2-萘羧酸（AHPN）抑制细胞增殖，是多种癌细胞系的有效凋亡诱导剂。为了更深入地了解ahpn诱导生长停滞和凋亡的机制，我们开始利用cDNA阵列筛选人肺癌H460细胞，检测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Nur77。AHPN能够增加多种癌细胞中Egr-1和Nur77 mRNA的表达和蛋白表达。这种诱导似乎在转录水平上受到调节，并且是AHPN特异性的，因为RAR-和rxr -选择性类视黄醛是无活性的。这些结果表明，AHPN对Egr-1和Nur77的诱导是独立于核类视黄酮受体的，并且涉及一种新的机制。在人T细胞淋巴瘤Molt-4细胞中，过表达Bcl-2可以抑制ahpn诱导的细胞凋亡，但不会抑制生长停滞，并且不会阻断立即早期基因表达的诱导。用AHPN处理H460细胞诱导p38 MAP-kinase激活，但不激活ERK1/2信号通路。然而，PD98059抑制ERK1/2信号通路阻断了Egr-1和Nur77 mRNA的诱导，而p38 MAPK抑制剂PD169316作用不大。显性阴性ERK1的表达完全消除了Egr-1 mRNA的增加，减少了AHPN对生长的抑制。我们的研究结果表明，AHPN在H460中诱导Egr-1需要活跃的ERK1/2，并且独立于p38的激活。Egr-1与其他几种生长抑制蛋白合作，可能参与了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.