Activation of Cyclin-Dependent Kinases by Fructose-2,6-Bisphosphate

描述（由申请人提供）：6-磷酸果糖-2-激酶/果糖-2,6-二磷酸酶（PFKFB）将果糖-6-磷酸（F6P）磷酸化为果糖-2,6-二磷酸（F2,6BP），这是6-磷酸果糖-1激酶的变链激活剂，是糖酵解途径中的限速酶。虽然有四种PFKFB酶，但PFKFB3和PFKFB4是特别感兴趣的，因为这些酶已被发现在人类癌症中被激活，通过HIF-1？在PFKFB3的情况下，它是ras转化肿瘤生长所必需的。为了更好地了解PFKFB2-4对糖酵解的相对贡献，我们检测了这些酶的亚细胞定位，并惊讶地发现，PFKFB2和PFKFB4定位于细胞质（糖酵解的部位），而PFKFB3定位于细胞核。然后，我们在HeLa细胞中过表达PFKFB3，观察到葡萄糖摄取没有变化，而是增殖增加。真核细胞分裂由细胞周期蛋白依赖激酶（CDKs）控制，细胞周期蛋白依赖激酶与调节细胞周期蛋白结合，磷酸化数百种控制DNA复制、转录和有丝分裂的底物。我们发现PFKFB3的过表达刺激了HeLa细胞中CDK1的活性，纯化的F2,6BP刺激了体外重组单体CDK1。然后，我们通过证明CDK1 siRNA而不是CDK2、CDK4或CDK6 siRNA逆转了由PFKFB3过表达引起的增殖增加，证实了CDK1对PFKFB3促增殖作用的要求。重要的是，转染了PFKFB3特异性siRNA的HeLa细胞降低了内源性PFKFB3，从而降低了CDK1活性，增加了p27的表达，抑制了G1/S转变，诱导了细胞凋亡，但对葡萄糖摄取没有影响。这些数据支持PFKFB3在调节细胞周期进程和凋亡中的独特作用，而不是葡萄糖代谢。我们提出验证由PFKFB3产生的核F2,6BP激活CDKs并促进细胞周期进程的假设。我们预计核F2,6BP可能在调节CDK1和其他CDKs中发挥独特的作用，并且抑制PFKFB3将抑制CDK活性，而不会显著影响转化细胞的糖代谢，而不会影响正常细胞。

DESCRIPTION (provided by applicant): The 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB) phosphorylate fructose-6-phosphate (F6P) to fructose-2,6-bisphosphate (F2,6BP), which is an allosteric activator of 6-phosphofructo-1-kinase, a rate-limiting enzyme in the glycolytic pathway. Although there are four PFKFB enzymes, PFKFB3 and PFKFB4 are of particular interest since these enzymes have been found to be activated in human cancers, to be increased by hypoxic exposure via HIF-1?, and, in the case of PFKFB3, to be required for the growth of Ras-transformed tumors. In order to better understand the relative contributions of PFKFB2-4 to glycolysis, we examined the subcellular localization of these enzymes and were surprised to find that whereas PFKFB2 and PFKFB4 localized to the cytoplasm (the site of glycolysis), PFKFB3 localized to the nucleus. We then over-expressed PFKFB3 in HeLa cells and observed no change in glucose uptake but rather an increase in proliferation. Eukaryotic cell division is controlled by cyclin dependent kinases (CDKs) that bind to regulatory cyclins and phosphorylate hundreds of substrates that control DNA replication, transcription and mitosis. We found that over-expression of PFKFB3 stimulated CDK1 activity in HeLa cells and that purified F2,6BP stimulated recombinant monomeric CDK1 in vitro. We then confirmed the requirement of CDK1 for the pro-proliferative effects of PFKFB3 by demonstrating that CDK1 siRNA but not CDK2, CDK4 or CDK6 siRNA reversed the increased proliferation caused by over-expression of PFKFB3. Importantly, transfection of HeLa cells with PFKFB3-specific siRNA decreased endogenous PFKFB3 which in turn reduced CDK1 activity, increased p27 expression, suppressed G1/S transition, induced apoptosis but had no impact on glucose uptake. These data support a distinct role for PFKFB3 in the regulation of cell cycle progression and apoptosis, and not glucose metabolism. We propose to test the hypothesis that nuclear F2,6BP generated by PFKFB3 activates CDKs and promotes cell cycle progression. We anticipate that nuclear F2,6BP may serve unique roles in regulating CDK1, and other CDKs, and that inhibition of PFKFB3 will suppress CDK activities without significantly affecting glucose metabolism in transformed but not in normal cells.