hnRNPA1 enhances FOXP3 stability to promote the differentiation and functions of regulatory T cells.

Regulatory T cells (Tregs) are indispensable for the maintenance of immunological self-tolerance and homeostasis. Heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) is required for optimal Treg induction. Here, we reveal that human-induced Tregs (iTregs) lacking hnRNPA1 show reduced expression of the transcription factor FOXP3, increased ubiquitination level of FOXP3, and impaired suppressive abilities. Human naïve CD4 T cells with hnRNPA1 knockdown show a decreased Treg differentiation ratio. hnRNPA1 could interact with FOXP3 as well as with the E3 ligase Stub1. The phosphorylation at hnRNPA1 S199 could increase both interactions. The overexpression of FOXP3 in Tregs containing shhnRNPA1 could not recover the phenotype caused by hnRNPA1 knockdown. Therefore, there might be multiple essential pathways regulated by hnRNPA1 in Tregs. In conclusion, we present a new role of hnRNPA1 in promoting Treg function, indicating it as a promising target for tumor therapies.

Liu X ，Tian N ，Huang Q ，Xu Z ，Cheng H ，Liu X ，Li D ，Liang R ，Li B ，Dai X ... -  《-》

Induction of CD4(+)CD25(+)FOXP3(+) regulatory T cells by mesenchymal stem cells is associated with modulation of ubiquitination factors and TSDR demethylation.

Khosravi M ，Bidmeshkipour A ，Cohen JL ，Moravej A ，Hojjat-Assari S ，Naserian S ，Karimi MH ... -  《-》

Ring finger protein 31-mediated atypical ubiquitination stabilizes forkhead box P3 and thereby stimulates regulatory T-cell function.

The CD4+CD25+FOXP3+ regulatory T (Treg) cells are critical for maintaining immune tolerance in healthy individuals and are reported to restrict anti-inflammatory responses and thereby promote tumor progression, suggesting them as a target in the development of antitumor immunotherapy. Forkhead box P3 (FOXP3) is a key transcription factor governing Treg lineage differentiation and their immune-suppressive function. Here, using Treg cells, as well as HEK-293T and Jurkat T cells, we report that the stability of FOXP3 is directly and positively regulated by the E3 ubiquitin ligase ring finger protein 31 (RNF31), which catalyzes the conjugation of atypical ubiquitin chains to the FOXP3 protein. We observed that shRNA-mediated RNF31 knockdown in human Treg cells decreases FOXP3 protein levels and increases levels of interferon-γ, resulting in a Th1 helper cell-like phenotype. Human Treg cells that ectopically expressed RNF31 displayed stronger immune-suppressive capacity, suggesting that RNF31 positively regulates both FOXP3 stability and Treg cell function. Moreover, we found that RNF31 is up-regulated in Treg cells that infiltrate human gastric tumor tissues compared with their counterparts residing in peripheral and normal tissue. We also found that elevated RNF31 expression in intratumoral Treg cells is associated with poor survival of gastric cancer patients, suggesting that RNF31 supports the immune-suppressive functions of Treg cells. Our results suggest that RNF31 could be a potential therapeutic target in immunity-based interventions against human gastric cancer.

Zhu F ，Yi G ，Liu X ，Zhu F ，Zhao A ，Wang A ，Zhu R ，Chen Z ，Zhao B ，Fang S ，Yu X ，Lin R ，Liang R ，Li D ，Zhao W ，Zhang Z ，Guo W ，Zhang S ，Ge S ，Fan X ，Zhao G ，Li B ... -  《-》

Mouse Double Minute 2 Homolog-Mediated Ubiquitination Facilitates Forkhead Box P3 Stability and Positively Modulates Human Regulatory T Cell Function.

Regulatory T cells (Treg cells) are essential for maintaining immune tolerance, and the dysfunction of Treg cells may cause autoimmune diseases and tumors. Forkhead box P3 (FOXP3) is the key transcription factor controlling Treg cell development and suppressive function. Mouse double minute 2 homolog (MDM2), an E3 ubiquitin ligase, has been identified as an oncoprotein that mediates the ubiquitination and degradation of tumor suppressor p53; however, whether it has functions in Treg cells remains unknown. Here, we demonstrate that MDM2 positively regulates human Treg cell suppressive function via its mediated ubiquitination and stabilization of FOXP3. Knockdown of MDM2 with shRNA in human primary Treg cells leads to the impaired ability of FOXP3 to regulate the expression levels of downstream genes and the attenuated suppressive capacity of Treg cells, due to FOXP3 instability. Consistently, MDM2 overexpression in human Treg cells enhances FOXP3 stability and Treg cell suppressive capacity. Mechanistically, MDM2 interacts with FOXP3, and mainly mediates monoubiquitination and polyubiquitination of FOXP3, thus stabilizing the protein level of FOXP3. We have also found lysine residues in FOXP3 required for MDM2-mediated ubiquitination. In addition, TCR/CD28 signaling upregulates the expression level of MDM2 and its mediated FOXP3 ubiquitination in human Treg cells. Therefore, our findings reveal that MDM2 in Treg cells could be a potential therapeutic target for treating autoimmune diseases and tumors.

Wang A ，Yang M ，Liang R ，Zhu F ，Zhu F ，Liu X ，Han Y ，Lin R ，Wang X ，Li D ，Li H ，Yuan X ，Zhao H ，Li B ... -  《-》

Foxp3 positive regulatory T cells: a functional regulation by the E3 ubiquitin ligase Itch.

Su J ，Liu YC 《-》