Department of Medicine, University of California-Irvine School of Medicine, Orange, CA 92868, USA.
Mol Cancer. 2010 Aug 11;9:214. doi: 10.1186/1476-4598-9-214.
As a survival factor for melanocytes lineage cells, MiTF plays multiple roles in development and melanomagenesis. What role MiTF plays in the DNA damage response is currently unknown. In this report we observed that MiTF was phosphorylated at serine 73 after UVC radiation, which was followed by proteasome-mediated degradation. Unlike after c-Kit stimulation, inhibiting p90RSK-1 did not abolish the band shift of MiTF protein, nor did it abolish the UVC-mediated MiTF degradation, suggesting that phosphorylation on serine 73 by Erk1/2 is a key event after UVC. Furthermore, the MiTF-S73A mutant (Serine 73 changed to Alanine via site-directed mutagenesis) was unable to degrade and was continuously expressed after UVC exposure. Compared to A375 melanoma cells expressing wild-type MiTF (MiTF-WT), cells expressing MiTF-S73A mutant showed less p21 WAF1/CIP1 accumulation and a delayed p21 WAF1/CIP1 recovery after UVC. Consequently, cells expressing MiTF-WT showed a temporary G1 arrest after UVC, but cells expressing MiTF-S73A mutant or lack of MiTF expression did not. Finally, cell lines with high levels of MiTF expression showed higher resistance to UVC-induced cell death than those with low-level MiTF. These data suggest that MiTF mediates a survival signal linking Erk1/2 activation and p21 WAF1/CIP1 regulation via phosphorylation on serine 73, which facilitates cell cycle arrest. In addition, our data also showed that exposure to different wavelengths of UV light elicited different signal pathways involving MiTF.
作为黑素细胞谱系细胞的生存因子，MiTF 在发育和黑色素瘤发生中发挥多种作用。MiTF 在 DNA 损伤反应中扮演什么角色目前尚不清楚。在本报告中，我们观察到 UVC 辐射后 MiTF 在丝氨酸 73 处发生磷酸化，随后发生蛋白酶体介导的降解。与 c-Kit 刺激不同，抑制 p90RSK-1 并不能消除 MiTF 蛋白的条带移位，也不能消除 UVC 介导的 MiTF 降解，这表明 Erk1/2 对丝氨酸 73 的磷酸化是 UVC 后的关键事件。此外，MiTF-S73A 突变体（通过定点突变将丝氨酸 73 突变为丙氨酸）无法降解，并且在 UVC 暴露后持续表达。与表达野生型 MiTF（MiTF-WT）的 A375 黑素瘤细胞相比，表达 MiTF-S73A 突变体的细胞在 UVC 后 p21 WAF1/CIP1 积累较少，p21 WAF1/CIP1 恢复延迟。因此，表达 MiTF-WT 的细胞在 UVC 后表现出短暂的 G1 期阻滞，但表达 MiTF-S73A 突变体或缺乏 MiTF 表达的细胞则没有。最后，MiTF 高表达的细胞系对 UVC 诱导的细胞死亡的抵抗力高于低表达 MiTF 的细胞系。这些数据表明，MiTF 通过丝氨酸 73 的磷酸化介导一条将 Erk1/2 激活与 p21 WAF1/CIP1 调节联系起来的生存信号，从而促进细胞周期阻滞。此外，我们的数据还表明，暴露于不同波长的紫外线会引发涉及 MiTF 的不同信号通路。
