Autoregulation of YB-1 Synthesis in Cells.

The Y-box binding protein 1 (YB-1) plays a crucial role in regulating essential cell functions, including transcription, translation, and DNA repair, through its interactions with nucleic acids and multiple protein partners. The multifunctionality of YB-1 makes the control of its levels critical for cellular homeostasis and adaptation to stress. The synthesis of YB-1 is regulated by gene transcription, protein stability (mediated by long non-coding RNAs), and translation of its mRNA. Autoregulation of mRNA translation remains the topic of ongoing debate. Some earlier studies suggested a role of the 5' untranslated region (UTR) in inhibiting protein synthesis, while others demonstrated the importance of YB-1 binding to the 3' UTR for reducing translation. This disagreement has been further complicated by the absence of evidence for these mechanisms in living cells. Here, we provide the first direct evidence that YB-1 represses its synthesis in cultured human cells. Using metabolic protein labeling and immunoprecipitation, we confirmed the effect of YB-1 on the translation of its mRNA. Experiments with reporter constructs showed that both UTRs of the mRNA are involved in autoregulation, thus resolving the contradiction in the literature. These results highlight a sophisticated mechanism for controlling YB-1 levels, which requires both 5' and 3' UTRs of the mRNA, and confirm their role in fine-tuning YB-1 synthesis.