Department of General Pathology, Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
Department of Neuropathology, Institute of Pathology, University Hospital Heidelberg, Heidelberg, Germany.
Cell Death Dis. 2020 Nov 30;11(11):1023. doi: 10.1038/s41419-020-03220-3.
Chromosome 8p is frequently deleted in various cancer entities and has been shown to correlate with poor patient survival. SH2D4A is located on chromosome 8p and prevents the nuclear translocation of the pro-tumorigenic transcription factor STAT3. Here, we investigated the interaction of SH2D4A and STAT3 to shed light on the non-canonical functions of STAT3 in cooperation with the tumor suppressor SH2D4A. Using an immunoprecipitation-mass spectrometry (IP-MS) approach, we identified the mitochondrial scaffold proteins prohibitin 1 (PHB1) and prohibitin 2 (PHB2) among other proteins to potentially bind to SH2D4A. Co-immunoprecipitation and proximity ligation assays confirmed direct interactions of STAT3, PHB1, and SH2D4A in situ and in vitro. In addition, cell fractionation and immunofluorescence staining revealed co-localization of these proteins with mitochondria. These interactions were selectively interrupted by the small molecule and PHB ligand FL3. Furthermore, FL3 led to a reduction of STAT3 protein levels, STAT3 transcriptional activity, and HIF1α protein stabilization upon dimethyloxalylglycine (DMOG) treatment. Besides, mitochondrial fusion and fission markers, L-OPA1, Mfn1, and FIS1, were dysregulated upon FL3 treatment. This dysregulated morphology was accompanied by significant reduction of mitochondrial respiration, thus, FL3 significantly diminished mitochondrial respirational capacity. In contrast, SH2D4A knockout increased mitochondrial respiration, whereas FL3 reversed the effect of SH2D4A knockout. The here described results indicate that the interaction of SH2D4A and PHB1 is involved in the mitochondrial function and integrity. The demonstrated interaction with STAT3, accompanied by its reduction of transcriptional activity, further suggests that SH2D4A is linking STAT3 to its mitochondrial functions, and inhibition of PHB-interaction may have therapeutic effects in tumor cells with STAT3 activation.
8 号染色体 p 区域在多种癌症实体中经常缺失,并与患者生存预后不良相关。SH2D4A 位于 8 号染色体 p 区域,可阻止致癌转录因子 STAT3 的核转位。在此,我们研究了 SH2D4A 和 STAT3 的相互作用,以阐明 SH2D4A 与肿瘤抑制因子合作时 STAT3 的非典型功能。我们使用免疫沉淀-质谱(IP-MS)方法,鉴定了线粒体支架蛋白 PHB1 和 PHB2 以及其他潜在与 SH2D4A 结合的蛋白。共免疫沉淀和邻近连接分析证实了 STAT3、PHB1 和 SH2D4A 在体内和体外的直接相互作用。此外,细胞分级分离和免疫荧光染色显示这些蛋白与线粒体共定位。这些相互作用可被小分子和 PHB 配体 FL3 选择性阻断。此外,FL3 导致 DMOG 处理时 STAT3 蛋白水平、STAT3 转录活性和 HIF1α 蛋白稳定性降低。此外,FL3 处理时线粒体融合和裂变标记物 L-OPA1、Mfn1 和 FIS1 失调。这种失调的形态伴随着线粒体呼吸的显著减少,因此,FL3 显著降低了线粒体呼吸能力。相反,SH2D4A 敲除增加了线粒体呼吸,而 FL3 逆转了 SH2D4A 敲除的作用。所描述的结果表明,SH2D4A 和 PHB1 的相互作用参与了线粒体的功能和完整性。与 STAT3 的相互作用及其转录活性的降低表明,SH2D4A 将 STAT3 与线粒体功能联系起来,抑制 PHB 相互作用可能对 STAT3 激活的肿瘤细胞具有治疗效果。