Leautaud Veronica, Demple Bruce
Department of Genetics and Complex Diseases, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
BMC Mol Biol. 2007 Dec 20;8:116. doi: 10.1186/1471-2199-8-116.
Heme oxygenase-1 (HO-1) catalizes heme degradation, and is considered one of the most sensitive indicators of cellular stress. Previous work in human fibroblasts has shown that HO-1 expression is induced by NO, and that transcriptional induction is only partially responsible; instead, the HO-1 mRNA half-life is substantially increased in response to NO. The mechanism of this stabilization remains unknown.
In NIH3T3 murine fibroblasts, NO exposure increased the half-life of the HO-1 transcript from ~1.6 h to 11 h, while treatments with CdCl2, NaAsO2 or H2O2 increased the half-life only up to 5 h. Although poly(A) tail shortening can be rate-limiting in mRNA degradation, the HO-1 mRNA deadenylation rate in NO-treated cells was ~65% of that in untreated controls. In untreated cells, HO-1 poly(A) removal proceeded until 30-50 nt remained, followed by rapid mRNA decay. In NO-treated cells, HO-1 deadenylation stopped with the mRNA retaining poly(A) tails 30-50 nt long. We hypothesize that NO treatment stops poly(A) tail shortening at the critical 30- to 50-nt length. This is not a general mechanism for the post-transcriptional regulation of HO-1 mRNA. Methyl methane sulfonate also stabilized HO-1 mRNA, but that was associated with an 8-fold decrease in the deadenylation rate compared to that of untreated cells. Another HO-1 inducer, CdCl2, caused a strong increase in the mRNA level without affecting the HO-1 mRNA half-life.
The regulation of HO-1 mRNA levels in response to cellular stress can be induced by transcriptional and different post-transcriptional events that act independently, and vary depending on the stress inducer. While NO appears to stabilize HO-1 mRNA by preventing the final steps of deadenylation, methyl methane sulfonate achieves stabilization through the regulation of earlier stages of deadenylation.
血红素加氧酶-1（HO-1）催化血红素降解，被认为是细胞应激最敏感的指标之一。先前在人成纤维细胞中的研究表明，HO-1表达由一氧化氮（NO）诱导，且转录诱导只是部分原因；相反，HO-1 mRNA半衰期因NO而显著延长。这种稳定性的机制尚不清楚。
在NIH3T3小鼠成纤维细胞中，暴露于NO使HO-1转录本的半衰期从约1.6小时增加到11小时，而用氯化镉（CdCl2）、亚砷酸钠（NaAsO2）或过氧化氢（H2O2）处理仅使半衰期增加到5小时。虽然聚腺苷酸（poly(A)）尾巴缩短在mRNA降解中可能是限速步骤，但经NO处理的细胞中HO-1 mRNA去腺苷酸化速率约为未处理对照细胞的65%。在未处理的细胞中，HO-1的poly(A)去除一直持续到剩余30 - 50个核苷酸，随后mRNA迅速降解。在经NO处理的细胞中，HO-1去腺苷酸化停止，mRNA保留30 - 50个核苷酸长的poly(A)尾巴。我们推测，NO处理在关键的30至50个核苷酸长度处停止poly(A)尾巴缩短。这不是HO-1 mRNA转录后调控的普遍机制。甲磺酸甲酯也使HO-1 mRNA稳定，但与未处理细胞相比，其去腺苷酸化速率降低了8倍。另一种HO-1诱导剂CdCl2使mRNA水平显著增加，但不影响HO-1 mRNA半衰期。
细胞应激时HO-1 mRNA水平的调节可由转录及不同的转录后事件独立诱导，且因应激诱导剂而异。虽然NO似乎通过阻止去腺苷酸化的最后步骤来稳定HO-1 mRNA，但甲磺酸甲酯通过调节去腺苷酸化的早期阶段实现稳定。
