Chromatin remodeler BRM is a key mediator of leucine-stimulated mTOR gene transcription in mouse mammary epithelial cells

Methionine and Leucine Promote mTOR Gene Transcription and Milk Synthesis in Mammary Epithelial Cells through the eEF1Bα-UBR5-ARID1A Signaling

Amino acids are essential for the activation of the mechanistic target of rapamycin (mTOR), but the corresponding molecular mechanism is not yet fully understood. We previously found that Met stimulated eukaryotic elongation factor α (eEF1Bα) nuclear localization in bovine mammary epithelial cells (MECs). Herein, we explored the role and molecular mechanism of eEF1Bα in methionine (Met)- and leucine (Leu)-stimulated mTOR gene transcription and milk synthesis in MECs. eEF1Bα knockdown decreased milk protein and fat synthesis, cell proliferation, and mTOR mRNA expression and phosphorylation, whereas eEF1Bα overexpression had the opposite effects. QE-MS analysis detected that eEF1Bα was phosphorylated at Ser106 in the nucleus and Met and Leu stimulated p-eEF1Bα nuclear localization. eEF1Bα knockdown abrogated the stimulation of Met and Leu by mTOR mRNA expression and phosphorylation, and this regulatory role was dependent on its phosphorylation. Akt knockdown blocked the stimulation of Met and Leu by eEF1Bα and p-eEF1Bα expression. ChIP-PCR detected that p-eEF1Bα bound only to the -548 to -793 nt site in the mTOR promoter, and ChIP-qPCR further detected that Met and Leu stimulated this binding. eEF1Bα mediated Met and Leu' stimulation on mTOR mRNA expression and phosphorylation through inducing AT-rich interaction domain 1A (ARID1A) ubiquitination degradation, and this process depended on eEF1Bα phosphorylation. p-eEF1Bα interacted with ARID1A and ubiquitin protein ligase E3 module N-recognition 5 (UBR5), and UBR5 knockdown rescued the decrease of the ARID1A protein level by eEF1Bα overexpression. Both eEF1Bα and p-eEF1Bα were highly expressed in mouse mammary gland tissues during the lactating period. In summary, we reveal that Met and Leu stimulate mTOR transcriptional activation and milk protein and fat synthesis in MECs through eEF1Bα-UBR5-ARID1A signaling.

Methionine Promotes Milk Synthesis through the BRCC36-BRG1-mTOR Signaling Axis in Mammary Epithelial Cells

Methionine (Met) functions as a key stimulator on the mTOR signaling pathway and milk synthesis, but the molecular mechanism remains incompletely understood. We investigated the regulatory roles of BRCC36 in Met-stimulated milk lipid and protein synthesis, cell proliferation, and the mTOR signaling pathway. Knockdown of BRCC36 promoted milk lipid and protein synthesis in HC11 cells as well as cell proliferation by increasing the levels of mTOR gene transcription and protein phosphorylation. Conversely, the gene activation of BRCC36 had opposite effects. Furthermore, BRCC36 gene activation completely blocked Met stimulation on the BRG1 protein level and mTOR mRNA level and protein phosphorylation. BRCC36 bound to BRG1, and BRCC36 and BRG1 bound to the same region on the mTOR promoter. BRCC36 inhibited the BRG1 protein level and the binding of BRG1 to the mTOR promoter. Met decreased the BRCC36 protein level, and this effect was significantly attenuated by MG132 but not affected by cycloheximide or chloroquine. We further showed that Met increased BRCC36 ubiquitination degradation. Our findings reveal that Met promotes milk lipid and protein synthesis in MECs through the BRCC36-BRG1-mTOR signaling axis.

Genetics, environmental stress, and amino acid supplementation affect lactational performance via mTOR signaling pathway in bovine mammary epithelial cells

Mammary glands are known for their ability to convert nutrients present in the blood into milk contents. In cows, milk synthesis and the proliferation of cow mammary epithelial cells (CMECs) are regulated by various factors, including nutrients such as amino acids and glucose, hormones, and environmental stress. Amino acids, in particular, play a crucial role in regulating cell proliferation and casein synthesis in mammalian epithelial cells, apart from being building blocks for protein synthesis. Studies have shown that environmental factors, particularly heat stress, can negatively impact milk production performance in dairy cattle. The mammalian target of rapamycin complex 1 (mTORC1) pathway is considered the primary signaling pathway involved in regulating cell proliferation and milk protein and fat synthesis in cow mammary epithelial cells in response to amino acids and heat stress. Given the significant role played by the mTORC signaling pathway in milk synthesis and cell proliferation, this article briefly discusses the main regulatory genes, the impact of amino acids and heat stress on milk production performance, and the regulation of mTORC signaling pathway in cow mammary epithelial cells.

Expression of mTOR in normal and pathological conditions

The mechanistic/mammalian target of rapamycin (mTOR), a protein discovered in 1991, integrates a complex pathway with a key role in maintaining cellular homeostasis. By comprising two functionally distinct complexes, mTOR complex 1 (mTORC1) and mTORC2, it is a central cellular hub that integrates intra- and extracellular signals of energy, nutrient, and hormone availability, modulating the molecular responses to acquire a homeostatic state through the regulation of anabolic and catabolic processes. Accordingly, dysregulation of mTOR pathway has been implicated in a variety of human diseases. While major advances have been made regarding the regulators and effectors of mTOR signaling pathway, insights into the regulation of mTOR gene expression are beginning to emerge. Here, we present the current available data regarding the mTOR expression regulation at the level of transcription, translation and mRNA stability and systematize the current knowledge about the fluctuations of mTOR expression observed in several diseases, both cancerous and non-cancerous. In addition, we discuss whether mTOR expression changes can be used as a biomarker for diagnosis, disease progression, prognosis and/or response to therapeutics. We believe that our study will contribute for the implementation of new disease biomarkers based on mTOR as it gives an exhaustive perspective about the regulation of mTOR gene expression in both normal and pathological conditions.