Tumor cells tend to metabolize glucose through aerobic glycolysis instead of oxidative phosphorylation in mitochondria. One of the rate limiting enzymes of glycolysis is 6-phosphofructo-1-kinase, which is allosterically activated by fructose 2,6-bisphosphate which in turn is produced by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2 or PFKFB). Mounting evidence suggests that cancerous tissues overexpress the PFKFB isoenzyme, PFKFB3, being causing enhanced proliferation of cancer cells. Initially, six PFKFB3 splice variants with different C-termini have been documented in humans. More recently, additional splice variants with varying N-termini were discovered the functions of which are to be uncovered. Glioblastoma is one of the deadliest forms of brain tumors. Up to now, the role of PFKFB3 splice variants in the progression and prognosis of glioblastomas is only partially understood. In this study, we first re-categorizedthe PFKFB3 splice variant repertoire to simplify the denomination. We investigated the impact of increased and decreased levels of PFKFB3-4(former UBI2K4 ) and PFKFB3-5 (former variant 5) on the viability and proliferation rate of glioblastoma U87 and HEK-293 cells. The simultaneous knock-down of PFKFB3-4 and PFKFB3-5led to a decrease in viability and proliferation of U87 and HEK-293 cells as well as a reduction in HEK-293 cell colony formation. Overexpression of PFKFB3-4 but not PFKFB3-5resulted in increased cell viability and proliferation. This finding contrasts withthe common notion that overexpression of PFKFB3 enhances tumor growth, but instead suggests splice variant-specific effects of PFKFB3, apparently with opposing effects on cell behaviour. Strikingly, in line with this result, we found that in human IDH-wildtype glioblastomas, the PFKFB3-4 to PFKFB3-5ratio was significantly shifted towards PFKFB3-4when compared to control brain samples. Our findings indicate that the expression level of distinct PFKFB3 splice variants impinges on tumorigenic properties of glioblastomas and that splice pattern may be of important diagnostic value for glioblastoma.

中文翻译：

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胶质母细胞瘤中PFKFB3剪接变体的功能多样性

肿瘤细胞倾向于通过有氧糖酵解而不是线粒体的氧化磷酸化来代谢葡萄糖。糖酵解的限速酶之一是6-磷酸果糖-1-激酶，它被果糖2,6-二磷酸变构激活，而果糖2,6-二磷酸又由6-磷酸果糖-2-激酶/果糖-2,6-二磷酸酶产生（ PFK-2 / FBPase-2或PFKFB）。越来越多的证据表明，癌组织过度表达PFKFB同工酶PFKFB3，导致癌细胞的增殖增强。最初，已在人类中记录了六个具有不同C末端的PFKFB3剪接变体。最近，发现了具有可变N末端的其他剪接变体，其功能将被发现。胶质母细胞瘤是脑肿瘤中最致命的形式之一。到现在，PFKFB3剪接变体在胶质母细胞瘤的进展和预后中的作用仅得到部分了解。在这项研究中，我们首先对PFKFB3剪接变体库进行了重新分类，以简化面额。我们研究了PFKFB3-4（原UBI2K4）和PFKFB3-5（原变异5）水平的升高和降低对胶质母细胞瘤U87和HEK-293细胞活力和增殖速率的影响。PFKFB3-4和PFKFB3-5的同时敲低导致U87和HEK-293细胞的活力和增殖降低，以及HEK-293细胞集落形成减少。PFKFB3-4的过表达而不是PFKFB3-5的过表达导致细胞活力和增殖的增加。这一发现与PFKFB3的过表达促进肿瘤生长的普遍观念形成了鲜明对比，但是相反，它提示了PFKFB3的剪接变体特异作用，显然对细胞行为具有相反的作用。令人惊讶的是，与该结果一致，我们发现在人IDH野生型胶质母细胞瘤中，与对照脑样本相比，PFKFB3-4与PFKFB3-5的比例显着向PFKFB3-4转移。我们的发现表明，不同的PFKFB3剪接变体的表达水平会影响胶质母细胞瘤的致瘤特性，并且剪接模式可能对胶质母细胞瘤具有重要的诊断价值。