Department of Biochemistry and Molecular Biology, BK21 Cell Transformation and Restoration, Ajou University School of Medicine, Suwon 443-721, Republic of Korea.
Eur J Cancer. 2012 Oct;48(15):2474-85. doi: 10.1016/j.ejca.2012.01.028. Epub 2012 Feb 14.
Mouse 12-O-tetradecanoyl phorbol-13-acetate inducible sequence 21 (TIS21), an orthologue of human B-cell translocation gene 2 (BTG2) and rat PC3, is a tumour suppressor that belongs to the antiproliferative gene family, and is implicated in a variety of biological processes. c-Myc is a transcription factor and its deregulation is common in leukaemia and lymphomas; the tumours are highly proliferative and often blocked at an earlier phase than the terminal stage of differentiation. The interrelation and the functional interplay of these two different proteins are not defined yet. We have shown here that the tumour suppressor TIS21 negatively regulated c-Myc expression during all-trans-retinoic acid (ATRA)-induced differentiation that accelerated differentiation and reduced proliferation of acute promyelocytic leukaemia (APL) HL-60 cells. TIS21 downregulated c-Myc mRNA and additionally decreased c-Myc protein stability by increasing its phosphorylation at S(62) and T(58) residues via activation of Erk1/2 and inhibition of PI3K/Akt along with the subsequent activation of GSK-3β in response to ATRA treatment. HL-60 cells treated with GSK-3β or proteosome inhibitors revealed marked accumulation of c-Myc both in the presence and absence of ATRA plus TIS21, confirming ATRA plus TIS21 mediated c-Myc phosphorylation and its consequent degradation in proteosome. Immunoprecipitation assay revealed that TIS21 hindered the interaction of p-Erk1/2 with Akt, thus directly regulating MAPK and Akt activities without interaction with c-Myc. These findings exhibit anticarcinogenic potential of TIS21 via downregulation of c-Myc expression during ATRA induced differentiation of HL-60 cells involving activation and deactivation of two major c-Myc regulators, Erk1/2 and Akt, respectively.
鼠 12-O-十四烷酰佛波醇-13-乙酸诱导序列 21（TIS21）是人类 B 细胞易位基因 2（BTG2）和大鼠 PC3 的同源物，是一种肿瘤抑制因子，属于抗增殖基因家族，参与多种生物学过程。c-Myc 是一种转录因子，其失调在白血病和淋巴瘤中很常见；肿瘤具有高度增殖性，并且通常在分化的早期阶段而不是终末阶段受阻。这两种不同蛋白质之间的相互关系和功能相互作用尚未确定。我们在这里表明，肿瘤抑制因子 TIS21 在全反式视黄酸（ATRA）诱导的分化过程中负调控 c-Myc 表达，从而加速急性早幼粒细胞白血病（APL）HL-60 细胞的分化并降低其增殖。TIS21 通过激活 Erk1/2 和抑制 PI3K/Akt，以及随后的 GSK-3β 激活来降低 c-Myc mRNA 的表达，并增加 c-Myc 蛋白的稳定性，从而增加其 S（62）和 T（58）残基的磷酸化。用 GSK-3β 或蛋白酶体抑制剂处理 HL-60 细胞，即使存在 ATRA 加 TIS21，也会导致 c-Myc 明显积累，证实 ATRA 加 TIS21 介导的 c-Myc 磷酸化及其随后在蛋白酶体中的降解。免疫沉淀测定显示 TIS21 阻碍了 p-Erk1/2 与 Akt 的相互作用，从而直接调节 MAPK 和 Akt 活性，而无需与 c-Myc 相互作用。这些发现表明 TIS21 通过下调 ATRA 诱导的 HL-60 细胞分化过程中 c-Myc 的表达，涉及激活和失活两种主要的 c-Myc 调节剂 Erk1/2 和 Akt，从而具有抗癌潜力。
