Unidad de Splicing, Instituto de Investigaciones Biomédicas de Barcelona-Consejo Superior de Investigaciones Científicas, Barcelona, Spain.
PLoS One. 2009 Dec 30;4(12):e8513. doi: 10.1371/journal.pone.0008513.
Three functional c-ras genes, known as c-H-ras, c-K-ras, and c-N-ras, have been largely studied in mammalian cells with important insights into normal and tumorigenic cellular signal transduction events. Two K-Ras mRNAs are obtained from the same pre-mRNA by alternative splicing. H-Ras pre-mRNA can also be alternatively spliced in the IDX and 4A terminal exons, yielding the p19 and p21 proteins, respectively. However, despite the Ras gene family's established role in tumorigenic cellular signal transduction events, little is known about p19 function. Previous results showed that p19 did not interact with two known p21 effectors, Raf1 and Rin1, but was shown to interact with RACK1, a scaffolding protein that promotes multi-protein complexes in different signaling pathways (Cancer Res 2003, 63 p5178). This observation suggests that p19 and p21 play differential and complementary roles in the cell.
We found that p19 regulates telomerase activity through its interaction with p73alpha/beta proteins. We also found that p19 overexpression induces G1/S phase delay; an observation that correlates with hypophosphorylation of both Akt and p70SK6. Similarly, we also observed that FOXO1 is upregulated when p19 is overexpressed. The three observations of (1) hypophosphorylation of Akt, (2) G1/S phase delay and (3) upregulation of FOXO1 lead us to conclude that p19 induces G1/S phase delay, thereby maintaining cells in a reversible quiescence state and preventing entry into apoptosis. We then assessed the effect of p19 RNAi on HeLa cell growth and found that p19 RNAi increases cell growth, thereby having the opposite effect of arrest of the G1/S phase or producing a cellular quiescence state.
Interestingly, p19 induces FOXO1 that in combination with the G1/S phase delay and hypophosphorylation of both Akt and p70SK6 leads to maintenance of a reversible cellular quiescence state, thereby preventing entry into apoptosis.
三种功能性 c-ras 基因，即 c-H-ras、c-K-ras 和 c-N-ras，在哺乳动物细胞中得到了广泛研究，对正常和肿瘤细胞信号转导事件有了重要的了解。两种 K-Ras mRNA 是由同一前体 mRNA 通过选择性剪接获得的。H-Ras 前体 mRNA 也可以在 IDX 和 4A 末端外显子中进行选择性剪接，分别产生 p19 和 p21 蛋白。然而，尽管 Ras 基因家族在肿瘤细胞信号转导事件中具有既定的作用，但人们对 p19 的功能知之甚少。先前的结果表明，p19 与两种已知的 p21 效应物 Raf1 和 Rin1 不相互作用，但与 RACK1 相互作用，RACK1 是一种支架蛋白，可促进不同信号通路中的多蛋白复合物（Cancer Res 2003，63 p5178）。这一观察结果表明，p19 和 p21 在细胞中发挥不同的互补作用。
我们发现 p19 通过与 p73alpha/beta 蛋白相互作用来调节端粒酶活性。我们还发现，p19 的过表达会导致 G1/S 期延迟；这一观察结果与 Akt 和 p70SK6 的低磷酸化相关。同样，当 p19 过表达时，我们还观察到 FOXO1 的上调。（1）Akt 的低磷酸化，（2）G1/S 期延迟和（3）FOXO1 的上调这三个观察结果使我们得出结论，p19 诱导 G1/S 期延迟，从而使细胞保持在可逆的静止状态，并防止进入凋亡。然后，我们评估了 p19 RNAi 对 HeLa 细胞生长的影响，发现 p19 RNAi 增加了细胞生长，从而产生了与 G1/S 期阻滞或产生细胞静止状态相反的效果。
有趣的是，p19 诱导 FOXO1，与 G1/S 期延迟以及 Akt 和 p70SK6 的低磷酸化相结合，导致可逆细胞静止状态的维持，从而防止进入凋亡。
