Maloy Abigail, Walter Sydney, Mascilli Arthur, Klein David C, Lardo Santana M, Londino James, Nyunoya Toru, McDyer John, Sun Mia, Zeng Xuemei, Yates Nathan, Cantrell Pamela, Hainer Sarah J, Mallampalli Rama K, Chandra Divay
Department of Medicine, University of Pittsburgh, Pittsburgh, PA.
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA.
bioRxiv. 2025 May 28:2025.05.23.653845. doi: 10.1101/2025.05.23.653845.
Forkhead Box Protein P1 (FoxP1) is a crucial transcriptional repressor essential for the development of the brain and heart. In adults, FoxP1 protein levels are dysregulated in a variety of disorders, including chronic obstructive pulmonary disease (COPD), atherosclerosis, and heart failure, where they causally contribute to disease pathogenesis. Although independent investigators have reported that FoxP1 protein is ubiquitinated, and E3 ligases have been identified for other FoxP family proteins, the identity of the E3 ligase that controls FoxP1 protein stability has remained unknown. Here, we identify FBXO24, a subunit of the Skp-Cullin-F-box (SCF) ubiquitin E3 ligase complex, as the regulator of FoxP1 ubiquitination and stability. Specifically, FBXO24 regulates K48 and K63 ubiquitination, complexes with, and co-localizes to the nucleus with FoxP1 protein in lung epithelial cells. Depleting FBXO24 reverses the unfolded protein response and cell death triggered by loss of FoxP1 protein in lung epithelium, suggesting a protective role. Additionally, FBXO24 knockout mice exhibit elevated FoxP1 levels in the lung and heart and reduced unfolded protein response activity after short-term cigarette smoke exposure. Intriguingly, we also uncovered bidirectional regulation, whereby FoxP1 protein binds to the FBXO24 promoter to suppress FBXO24 transcription. To our knowledge, this is the first evidence that a substrate for an E3 ligase can also regulate the E3 ligase and, therefore, control levels of other substrates, revealing new regulatory networks. Targeting FBXO24 may offer a therapeutic strategy for COPD, atherosclerosis, and heart failure by stabilizing FoxP1 levels in the heart and lungs and mitigating harmful downstream effects.
叉头框蛋白P1（FoxP1）是一种关键的转录抑制因子，对大脑和心脏的发育至关重要。在成年人中，FoxP1蛋白水平在多种疾病中失调，包括慢性阻塞性肺疾病（COPD）、动脉粥样硬化和心力衰竭，它在这些疾病的发病机制中起着因果作用。尽管独立研究人员报告称FoxP1蛋白会发生泛素化，并且已经鉴定出其他FoxP家族蛋白的E3连接酶，但控制FoxP1蛋白稳定性的E3连接酶的身份仍然未知。在这里，我们确定Skp-Cullin-F-box（SCF）泛素E3连接酶复合物的一个亚基FBXO24是FoxP1泛素化和稳定性的调节因子。具体而言，FBXO24调节K48和K63泛素化，与肺上皮细胞中的FoxP1蛋白形成复合物并共定位于细胞核。耗尽FBXO24可逆转肺上皮细胞中因FoxP1蛋白缺失引发的未折叠蛋白反应和细胞死亡，提示其具有保护作用。此外，FBXO24基因敲除小鼠在短期接触香烟烟雾后，肺和心脏中的FoxP1水平升高，未折叠蛋白反应活性降低。有趣的是，我们还发现了双向调节，即FoxP1蛋白与FBXO24启动子结合以抑制FBXO24转录。据我们所知，这是E3连接酶的底物也能调节E3连接酶并因此控制其他底物水平的首个证据，揭示了新的调控网络。靶向FBXO24可能通过稳定心脏和肺部的FoxP1水平并减轻有害的下游效应，为COPD、动脉粥样硬化和心力衰竭提供一种治疗策略。
