Rodriguez Pedro, Rojas Juan
Facultad de Ciencias M, é, dicas, Escuela de Medicina, Universidad de Santiago de Chile (USACH), el Belloto 3530, segundo piso. Avenida Libertador Bernardo O'Higgins n°3363, Estación Central, Santiago, Chile.
J Cell Biochem. 2016 Mar;117(3):741-50. doi: 10.1002/jcb.25359. Epub 2015 Sep 17.
cAMP is a second messenger well documented to be involved in the phosphorylation of PKA, MAP kinase, and histone H3 (H3). Early, we reported that cAMP also induced H3 dephosphorylation in a variety of proliferating cell lines. Herein, it is shown that cAMP elicits a biphasic H3 dephosphorylation independent of PKA activation in cycling cells. H89, a potent inhibitor of PKA catalytic sub-unite, could not abolish this effect. Additionally, H89 induces a rapid and biphasic H3 serine 10 dephosphorylation, while a decline in the basal phosphorylation of CREB/ATF-1 is observed. Rp-cAMPS, an analog of cAMP and specific inhibitor of PKA, is unable to suppress cAMP-mediated H3 dephosphorylation, whereas Rp-cAMPS effectively blocks CREB/ATF-1 hyper-phosphorylation by cAMP and its inducers. Interestingly, cAMP exerts a rapid and profound H3 dephosphorylation at much lower concentration (50-fold lower, 0.125 mM) than the concentration required for maximal CREB/ATF-1 phosphorylation (5 mM). Much higher cAMP concentration is required to fully induce CREB/ATF-1 gain in phosphate (5 mM), which correlates with the inhibition of H3 dephosphorylation. Also, the dephosphorylation of H3 does not overlap at onset of MAP kinase phosphorylation pathways, p38 and ERK. Surprisingly, rapamycin (an mTOR inhibitor), cAMP, and its natural inducer isoproterenol, elicit identical dephosphorylation kinetics on both S6K1 ribosomal kinase (a downstream mTOR target) and H3. Finally, cAMP-induced H3 dephosphorylation is PP1/2-dependent. The results suggest that a pathway, requiring much lower cAMP concentration to that required for CREB/ATF-1 hyper-phosphorylation, is responsible for histone H3 dephosphorylation and may be linked to mTOR down regulation.
环磷酸腺苷（cAMP）作为第二信使，在蛋白激酶A（PKA）、丝裂原活化蛋白激酶（MAP激酶）和组蛋白H3（H3）的磷酸化过程中发挥作用，这一点已有充分记录。早期，我们报道cAMP还能在多种增殖细胞系中诱导H3去磷酸化。本文表明，在循环细胞中，cAMP引发了一种与PKA激活无关的双相H3去磷酸化。H89是一种有效的PKA催化亚基抑制剂，无法消除这种效应。此外，H89诱导了快速且双相的H3丝氨酸10去磷酸化，同时观察到CREB/ATF-1的基础磷酸化水平下降。Rp-cAMPS是cAMP的类似物和PKA的特异性抑制剂，无法抑制cAMP介导的H3去磷酸化，而Rp-cAMPS能有效阻断cAMP及其诱导剂对CREB/ATF-1的过度磷酸化。有趣的是，与最大程度磷酸化CREB/ATF-1所需的浓度（5 mM）相比，cAMP在低得多的浓度（低50倍，0.125 mM）下就能迅速且显著地诱导H3去磷酸化。完全诱导CREB/ATF-1磷酸化增加需要更高的cAMP浓度（5 mM），这与H3去磷酸化的抑制相关。此外，H3的去磷酸化与MAP激酶磷酸化途径（p38和ERK）的起始阶段并不重叠。令人惊讶的是，雷帕霉素（一种mTOR抑制剂）、cAMP及其天然诱导剂异丙肾上腺素，对S6K1核糖体激酶（mTOR的下游靶点）和H3引发相同的去磷酸化动力学。最后，cAMP诱导的H3去磷酸化依赖于PP1/2。结果表明，一条需要比CREB/ATF-1过度磷酸化所需浓度低得多的cAMP浓度的途径，负责组蛋白H3去磷酸化，并且可能与mTOR下调有关。
