Thangaraju Muthusamy, Carswell Kristina N, Prasad Puttur D, Ganapathy Vadivel
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912, USA.
Biochem J. 2009 Jan 1;417(1):379-89. doi: 10.1042/BJ20081132.
Human colon cancer cells and primary colon cancer silence the gene coding for LDH (lactate dehydrogenase)-B and up-regulate the gene coding for LDH-A, resulting in effective conversion of pyruvate into lactate. This is associated with markedly reduced levels of pyruvate in cancer cells compared with non-malignant cells. The silencing of LDH-B in cancer cells occurs via DNA methylation, with involvement of the DNMTs (DNA methyltransferases) DNMT1 and DNMT3b. Colon cancer is also associated with the expression of pyruvate kinase M2, a splice variant with low catalytic activity. We have shown recently that pyruvate is an inhibitor of HDACs (histone deacetylases). Here we show that pyruvate is a specific inhibitor of HDAC1 and HDAC3. Lactate has no effect on any of the HDACs examined. Colon cancer cells exhibit increased HDAC activity compared with non-malignant cells. HDAC1 and HDAC3 are up-regulated in colon cancer cells and in primary colon cancer, and siRNA (small interfering RNA)-mediated silencing of HDAC1 and HDAC3 in colon cancer cells induces apoptosis. Colon cancer cells silence SLC5A8, the gene coding for a Na(+)-coupled pyruvate transporter. Heterologous expression of SLC5A8 in the human colon cancer cell line SW480 leads to inhibition of HDAC activity when cultured in the presence of pyruvate. This process is associated with an increase in intracellular levels of pyruvate, increase in the acetylation status of histone H4, and enhanced cell death. These studies show that cancer cells effectively maintain low levels of pyruvate to prevent inhibition of HDAC1/HDAC3 and thereby to evade cell death.
人结肠癌细胞和原发性结肠癌会使编码乳酸脱氢酶（LDH）-B的基因沉默，并上调编码LDH-A的基因，从而有效地将丙酮酸转化为乳酸。与非恶性细胞相比，这与癌细胞中丙酮酸水平的显著降低有关。癌细胞中LDH-B的沉默是通过DNA甲基化发生的，涉及DNA甲基转移酶（DNMTs）DNMT1和DNMT3b。结肠癌还与丙酮酸激酶M2的表达有关，丙酮酸激酶M2是一种催化活性较低的剪接变体。我们最近发现丙酮酸是组蛋白脱乙酰酶（HDACs）的抑制剂。在此我们表明丙酮酸是HDAC1和HDAC3的特异性抑制剂。乳酸对所检测的任何HDAC均无影响。与非恶性细胞相比，结肠癌细胞表现出HDAC活性增加。HDAC1和HDAC3在结肠癌细胞和原发性结肠癌中上调，并且在结肠癌细胞中通过小干扰RNA（siRNA）介导的HDAC1和HDAC3沉默可诱导细胞凋亡。结肠癌细胞使编码Na(+)-偶联丙酮酸转运体的基因SLC5A8沉默。在人结肠癌细胞系SW480中异源表达SLC5A8，当在丙酮酸存在下培养时会导致HDAC活性受到抑制。这一过程与细胞内丙酮酸水平的增加、组蛋白H4乙酰化状态的增加以及细胞死亡增强有关。这些研究表明，癌细胞有效地维持低水平的丙酮酸以防止HDAC1/HDAC3受到抑制，从而逃避细胞死亡。
