State Key Laboratory of Pharmaceutical Biotechnology and MOE Key Laboratory of Model Animals for Disease Study, Model Animal Research Center of Nanjing University, Nanjing, 210061, China.
Department of Molecular Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, 75390, USA.
Sci Rep. 2017 Jun 6;7(1):2891. doi: 10.1038/s41598-017-03165-2.
Hedgehog (Hh) signaling plays a pivotal role in animal development and its deregulation in humans causes birth defects and several types of cancer. Protein Kinase A (PKA) modulates Hh signaling activity through phosphorylating the transcription factor Cubitus interruptus (Ci) and G protein coupled receptor (GPCR) family protein Smoothened (Smo) in Drosophila, but how PKA activity is regulated remains elusive. Here, we identify a novel regulator of the Hh pathway, the capping-enzyme mRNA-cap, which positively regulates Hh signaling activity through modulating PKA activity. We provide genetic and biochemical evidence that mRNA-cap inhibits PKA kinase activity to promote Hh signaling. Interestingly, regulation of Hh signaling by mRNA-cap depends on its cytoplasmic capping-enzyme activity. In addition, we show that the mammalian homolog of mRNA-cap, RNGTT, can replace mRNA-cap to play the same function in the Drosophila Hh pathway and that knockdown of Rngtt in cultured mammalian cells compromised Shh pathway activity, suggesting that RNGTT is functionally conserved. Our study makes an unexpected link between the mRNA capping machinery and the Hh signaling pathway, unveils a new facet of Hh signaling regulation, and reveals a potential drug target for modulating Hh signaling activity.
刺猬（Hh）信号在动物发育中起着至关重要的作用，其在人类中的失调会导致出生缺陷和几种类型的癌症。蛋白激酶 A（PKA）通过磷酸化转录因子 Cubitus interruptus（Ci）和果蝇中的 G 蛋白偶联受体（GPCR）家族蛋白 Smoothened（Smo）来调节 Hh 信号活性，但 PKA 活性如何调节仍然难以捉摸。在这里，我们鉴定了 Hh 途径的一种新的调节剂，mRNA-帽，它通过调节 PKA 活性来正向调节 Hh 信号活性。我们提供了遗传和生化证据表明，mRNA-帽抑制 PKA 激酶活性以促进 Hh 信号。有趣的是，mRNA-帽对 Hh 信号的调节取决于其细胞质帽酶活性。此外，我们表明，mRNA-帽的哺乳动物同源物 RNGTT 可以替代 mRNA-帽在果蝇 Hh 途径中发挥相同的功能，并且在培养的哺乳动物细胞中敲低 Rngtt 会损害 Shh 途径活性，表明 RNGTT 在功能上是保守的。我们的研究在 mRNA 加帽机制和 Hh 信号通路之间建立了一个意想不到的联系，揭示了 Hh 信号调节的一个新方面，并揭示了调节 Hh 信号活性的潜在药物靶点。
