Chuang Jian-Ying, Wang Yi-Ting, Yeh Shiu-Hwa, Liu Yi-Wen, Chang Wen-Chang, Hung Jan-Jong
Institute of Basic Medical Sciences, College of Medicine, National Cheng-Kung University, Tainan 701, Taiwan.
Mol Biol Cell. 2008 Mar;19(3):1139-51. doi: 10.1091/mbc.e07-09-0881. Epub 2008 Jan 16.
The transcription factor Sp1 is ubiquitously expressed in different cells and thereby regulates the expression of genes involved in many cellular processes. This study reveals that Sp1 was phosphorylated during the mitotic stage in three epithelial tumor cell lines and one glioma cell line. By using different kinase inhibitors, we found that during mitosis in HeLa cells, the c-Jun NH(2)-terminal kinase (JNK) 1 was activated that was then required for the phosphorylation of Sp1. In addition, blockade of the Sp1 phosphorylation via inhibition JNK1 activity in mitosis resulted in the ubiquitination and degradation of Sp1. JNK1 phosphorylated Sp1 at Thr278/739. The Sp1 mutated at Thr278/739 was unstable during mitosis, possessing less transcriptional activity for the 12(S)-lipoxygenase expression and exhibiting a decreased cell growth rate compared with wild-type Sp1 in HeLa cells. In N-methyl-N-nitrosourea-induced mammary tumors, JNK1 activation provided a potential relevance with the accumulation of Sp1. Together, our results indicate that JNK1 activation is necessary to phosphorylate Sp1 and to shield Sp1 from the ubiquitin-dependent degradation pathway during mitosis in tumor cell lines.
转录因子Sp1在不同细胞中普遍表达，从而调节参与许多细胞过程的基因的表达。本研究表明，在三种上皮肿瘤细胞系和一种胶质瘤细胞系的有丝分裂阶段，Sp1发生了磷酸化。通过使用不同的激酶抑制剂，我们发现，在HeLa细胞有丝分裂期间，c-Jun氨基末端激酶（JNK）1被激活，随后该激酶是Sp1磷酸化所必需的。此外，在有丝分裂过程中通过抑制JNK1活性来阻断Sp1磷酸化，会导致Sp1的泛素化和降解。JNK1在Thr278/739位点使Sp1磷酸化。在Thr278/739位点发生突变的Sp1在有丝分裂期间不稳定，与HeLa细胞中的野生型Sp1相比，其对12(S)-脂氧合酶表达的转录活性较低，并且细胞生长速率降低。在N-甲基-N-亚硝基脲诱导的乳腺肿瘤中，JNK1激活与Sp1的积累具有潜在相关性。总之，我们的结果表明，在肿瘤细胞系有丝分裂期间，JNK1激活对于Sp1磷酸化以及保护Sp1免受泛素依赖性降解途径的影响是必要的。
