Picco María Elisa, Castro María Victoria, Quezada María Josefina, Barbero Gastón, Villanueva María Belén, Fernández Natalia Brenda, Kim Hyungsoo, Lopez-Bergami Pablo
1Instituto de Medicina y Biología Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
2Centro de Estudios Biomédicos, Biotecnológicos, Ambientales y Diagnóstico (CEBBAD), Universidad Maimónides, CONICET, Hidalgo 775, 6th Floor, Lab 602, Buenos Aires, Argentina.
Cell Biosci. 2019 Jan 3;9:3. doi: 10.1186/s13578-018-0265-8. eCollection 2019.
The PI3K/Akt and the STAT3 pathways are functionally associated in many tumor types. Both in vitro and in vivo studies have revealed that either biochemical or genetic manipulation of the STAT3 pathway activity induce changes in the same direction in Akt activity. However, the implicated mechanism has been poorly characterized. Our goal was to characterize the precise mechanism linking STAT3 with the activity of Akt and other AGC kinases in cancer using melanoma cells as a model.
We show that active STAT3 is constitutively bound to the PDK1 promoter and positively regulate PDK1 transcription through two STAT3 responsive elements. Transduction of WM9 and UACC903 melanoma cells with STAT3-small hairpin RNA decreased both PDK1 mRNA and protein levels. STAT3 knockdown also induced a decrease of the phosphorylation of AGC kinases Akt, PKC, and SGK. The inhibitory effect of STAT3 silencing on Akt phosphorylation was restored by HA-PDK1. Along this line, HA-PDK1 expression significantly blocked the cell death induced by dacarbazine plus STAT3 knockdown. This effect might be mediated by Bcl2 proteins since HA-PDK1 rescued Bcl2, Bcl-XL, and Mcl1 levels that were down-regulated upon STAT3 silencing.
We show that PDK1 is a transcriptional target of STAT3, linking STAT3 pathway with AGC kinases activity in melanoma. These data provide further rationale for the ongoing effort to therapeutically target STAT3 and PDK1 in melanoma and, possibly, other malignancies.
PI3K/Akt和STAT3信号通路在多种肿瘤类型中存在功能关联。体外和体内研究均表明，对STAT3信号通路活性进行生化或基因操作会导致Akt活性发生同向变化。然而，其中涉及的机制尚未得到充分阐明。我们的目标是以黑色素瘤细胞为模型，明确STAT3与癌症中Akt及其他AGC激酶活性之间联系的精确机制。
我们发现，活性STAT3持续结合于PDK1启动子，并通过两个STAT3反应元件正向调控PDK1转录。用STAT3小发夹RNA转导WM9和UACC903黑色素瘤细胞可降低PDK1的mRNA和蛋白水平。敲低STAT3还会导致AGC激酶Akt、PKC和SGK的磷酸化水平降低。HA-PDK1可恢复STAT3沉默对Akt磷酸化的抑制作用。同样，HA-PDK1表达可显著阻断达卡巴嗪加STAT3敲低诱导的细胞死亡。这种效应可能由Bcl2蛋白介导，因为HA-PDK1可挽救STAT3沉默后下调的Bcl2、Bcl-XL和Mcl1水平。
我们表明，PDK1是STAT3的转录靶点，在黑色素瘤中将STAT3信号通路与AGC激酶活性联系起来。这些数据为目前在黑色素瘤及可能的其他恶性肿瘤中靶向STAT3和PDK1进行治疗的研究提供了进一步的理论依据。
