Schwartz B, Avivi-Green C, Polak-Charcon S
Institute of Biochemistry, Food Science and Nutrition, Faculty of Agriculture, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Israel.
Mol Cell Biochem. 1998 Nov;188(1-2):21-30.
Sodium butyrate causes alteration of colon cancer cell morphology and biology towards that of a more differentiated phenotype. The retinoblastoma gene encodes a nuclear phosphoprotein (pRb) present in a wide range of human cancer cell lines including colon cancer cell lines. pRB is synthesized throughout the cell cycle and phosphorylated in a phase specific manner: the predominant proteins in G0/G1 are the unphosphorylated species (110 kD) whereas phosphorylated pRb (112-114 kD) are in S and G2. 110 kD pRb binds transcription factors and prevents transcription of responsive genes such as the gene for thymidine kinase, which are expressed in late G1. The precise mechanisms controlling cell arrest are unknown, but recent data suggest that cyclin-dependent kinase inhibitors such as p16 may play a role. The aim of the present study was to assess the effect of sodium butyrate on cell cycle staging, thymidine kinase activity, phosphorylation of the pRb protein and expression of p16. We show that sodium butyrate treatment induces differentiation of LS174T colon cancer cells, inhibits thymidine kinase activity concomitantly with induction of pRb dephosphorylation, p16 transcription and cell cycle arrest at G0/G1. Initial dephosphorylation was observed 24 h after treatment of LS174T cells with sodium butyrate, whereas complete shift to the dephosphorylated form was observed 3 days after treatment. Induction of pRb dephosphorylation by sodium butyrate preceded inhibition of growth and the specific cell cycle arrest. RNase protection assay with a p16 specific riboprobe showed undetectable levels in proliferating cells to several fold increase in differentiated colonocytes. In conclusion, the results provide evidence for a specific cellular mechanism of butyrate induced growth arrest and differentiation of a colon cancer cell line.
丁酸钠可使结肠癌细胞的形态和生物学特性发生改变，使其向更具分化表型的方向发展。视网膜母细胞瘤基因编码一种核磷蛋白（pRb），该蛋白存在于包括结肠癌细胞系在内的多种人类癌细胞系中。pRB在整个细胞周期中合成，并以阶段特异性方式磷酸化：G0/G1期的主要蛋白是未磷酸化的形式（110 kD），而磷酸化的pRb（112 - 114 kD）则存在于S期和G2期。110 kD的pRb与转录因子结合，阻止响应基因（如胸苷激酶基因）的转录，这些基因在G1晚期表达。控制细胞停滞的精确机制尚不清楚，但最近的数据表明，细胞周期蛋白依赖性激酶抑制剂如p16可能发挥作用。本研究的目的是评估丁酸钠对细胞周期分期、胸苷激酶活性、pRb蛋白磷酸化以及p16表达的影响。我们发现，丁酸钠处理可诱导LS174T结肠癌细胞分化，抑制胸苷激酶活性，同时诱导pRb去磷酸化、p16转录以及细胞周期停滞在G0/G1期。在用丁酸钠处理LS174T细胞24小时后观察到初始去磷酸化，而在处理3天后观察到完全转变为去磷酸化形式。丁酸钠诱导pRb去磷酸化先于生长抑制和特定的细胞周期停滞。用p16特异性核糖探针进行的核糖核酸酶保护分析显示，增殖细胞中p16水平不可检测，而在分化的结肠细胞中增加了几倍。总之，这些结果为丁酸盐诱导结肠癌细胞系生长停滞和分化的特定细胞机制提供了证据。
