Hypoxia-inducible Factor-1 (cid:1) mRNA Contains an Internal Ribosome Entry Site That Allows Efﬁcient Translation during Normoxia and Hypoxia-猫眼课题宝

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HIF-1（cid：1）是HIF-1转录因子的调节亚基，其诱导参与细胞对缺氧反应的许多基因的转录。HIF-1（cid：1）蛋白在供应充足氧气的细胞中迅速降解，但在缺氧细胞中稳定。使用多核糖体分析，我们发现NIH 3 T3细胞中HIF-1（cid：1）mRNA的翻译避免了缺氧期间发生的翻译速率的普遍降低。为了评估HIF-1（cid：1）mRNA的5（cid：1）UTR是否含有内部核糖体进入位点（IRES），我们构建了一个双顺反子报告基因，其中HIF-1（cid：1）5（cid：1）UTR插入两个报告基因编码区之间。我们发现HIF-1（cid：1）5（cid：1）UTR促进下游报告基因的翻译，表明存在IRES。IRES的活性与已充分表征的c-myc IRES的活性相当。IRES活性不受缺氧条件，导致减少帽依赖的翻译，和IRES活性受血清饥饿的影响比帽依赖的翻译。这些数据表明，HIF-1（cid：1）5（cid：1）UTR中IRES的存在允许在抑制帽依赖性翻译的条件下维持翻译。缺氧时，GAPDH少于HIF-1（cid：1）或两者生长下只有50-60%的mRNA沉积在多核糖体区域内。(cid：1）和压制我们没有进一步调查，让翻译不像

HIF-1 (cid:1) is the regulated subunit of the HIF-1 transcription factor, which induces transcription of a number of genes involved in the cellular response to hypoxia. The HIF-1 (cid:1) protein is rapidly degraded in cells supplied with adequate oxygen but is stabilized in hypoxic cells. Using polysome proﬁle analysis, we found that translation of HIF-1 (cid:1) mRNA in NIH3T3 cells is spared the general reduction in translation rate that occurs during hypoxia. To assess whether the 5 (cid:1) UTR of the HIF-1 (cid:1) mRNA contains an internal ribosome entry site (IRES), we constructed a dicistronic reporter with the HIF-1 (cid:1) 5 (cid:1) UTR inserted between two reporter coding regions. We found that the HIF-1 (cid:1) 5 (cid:1) UTR promoted translation of the downstream reporter, indicating the presence of an IRES. The IRES had activity comparable to that of the well-characterized c- myc IRES. IRES activity was not affected by hypoxic conditions that caused a reduction in cap-dependent translation, and IRES activity was less affected by serum-starvation than was cap-dependent translation. These data indicate that the presence of an IRES in the HIF-1 (cid:1) 5 (cid:1) UTR allows translation to be maintained under conditions that are inhibitory to cap-dependent translation. hypoxia, the GAPDH less than HIF-1 (cid:1) or under both growth only 50–60% of mRNA sedimenting within polysome region. (cid:1) and suppressed We have not further investigated that allow translation Unlike

Hypoxia-inducible Factor-1 (cid:1) mRNA Contains an Internal Ribosome Entry Site That Allows Efﬁcient Translation during Normoxia and Hypoxia

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