PKM2 knockdown influences SREBP activation and lipid synthesis in bovine mammary-gland epithelial MAC-T cells

Exploring the diverse role of pyruvate kinase M2 in cancer: Navigating beyond glycolysis and the Warburg effect

Pyruvate Kinase M2, a key enzyme in glycolysis, has garnered significant attention in cancer research due to its pivotal role in the metabolic reprogramming of cancer cells. Originally identified for its association with the Warburg effect, PKM2 has emerged as a multifaceted player in cancer biology. The functioning of PKM2 is intricately regulated at multiple levels, including controlling the gene expression via various transcription factors and non-coding RNAs, as well as adding post-translational modifications that confer distinct functions to the protein. Here, we explore the diverse functions of PKM2, encompassing newly emerging roles in non-glycolytic metabolic regulation, immunomodulation, inflammation, DNA repair and mRNA processing, beyond its canonical role in glycolysis. The ever-expanding list of its functions has recently grown to include roles in subcellular compartments such as the mitochondria and extracellular milieu as well, all of which make PKM2 an attractive drug target in the pursuit of therapeutics for cancer.

Valine promotes milk synthesis by regulating PKM2 nuclear accumulation and histone H3 acetylation through the TAS1R1-mTOR-DDX39B signaling pathway

Valine, a branched-chain amino acid found in dairy cows, has been recognized for its critical role in milk synthesis. However, the precise effect of valine on lactation in dairy cows remains an area of investigation. In our study, bovine mammary epithelial cells (BMECs) were isolated to explore the mechanism through which valine enhances milk synthesis. The results showed that 100 μM valine significantly boosted the milk synthesis via TAS1R1-mTOR-DDX39B signaling pathway in BMECs. Subsequent investigations revealed that DDX39B governs the accumulation of PKM2 in the nuclei of BMECs. This nuclear buildup of PKM2 weakened the interaction between HDAC3 and histone H3, leading to an increase in the acetylation levels of histone H3. In an vivo context, the 0.25 % valine-enriched drinking water notably elevated in the expression of milk protein and fat in these mice. Further examination showed that 0.25 % valine drinking water considerably augmented the protein expression levels of DDX39B, PKM2, and p-mTOR in the mice mammary glands. In summary, our results suggest that valine, by modulating the TAS1R1-mTOR-DDX39B signaling pathway, directs the accumulation of PKM2 in the nucleus. This, in turn, escalates the acetylation levels of histone H3, promoting the synthesis of both milk protein and fat.

KRAS Affects the Lipid Composition by Regulating Mitochondrial Functions and MAPK Activation in Bovine Mammary Epithelial Cells

Kirsten rat sarcoma viral oncogene homolog (KRAS), or guanosine triphosphatase KRAS, is a proto-oncogene that encodes the small guanosine triphosphatase transductor protein. Previous studies have found that KRAS can promote cytokine secretion, cell chemotaxis, and survival. However, its effects on milk fat synthesis in bovine mammary epithelial cells are unclear. In this study, the effects of KRAS inhibition on cell metabolism, autophagy, oxidative stress, endoplasmic reticulum stress, mitochondrial function, and lipid composition as well as the potential mechanisms were detected in an immortalized dairy cow mammary epithelial cell line (MAC-T). The results showed that inhibition of KRAS changed the lipid composition (especially the triglyceride level), mitochondrial functions, autophagy, and endoplasmic reticulum stress in cells. Moreover, KRAS inhibition regulated the levels of the mammalian target of rapamycin and mitogen-activated protein kinase (extracellular regulated protein kinases, c-Jun N-terminal kinases, p38) activation. These results indicated that regulation of KRAS would affect the synthesis and composition of milk fat. These results are also helpful for exploring the synthesis and secretion of milk fat at the molecular level and provide a theoretical basis for improving the percentage of fat in milk and the yield of milk from cows.

1α,25(OH)2 D3 alleviates high glucose-induced lipid accumulation in rat renal tubular epithelial cells by inhibiting SREBPs

Lipid accumulation is a vital event in the progression of diabetic nephropathy. 1,25-Dihydroxyvitamin D3 (1α,25(OH)₂ D₃ ) is considered to have a protective effect on diabetic nephropathy. However, it remains unclear whether 1α,25(OH)₂ D₃ can inhibit lipid accumulation, and the potential mechanisms responsible for lipid metabolism are incompletely understood. In this study, we evaluated the effects of 1α,25(OH)₂ D₃ on lipid metabolism in high glucose-exposed rat renal tubular epithelial NRK-52E cells. Results indicated that high glucose-enhanced lipid accumulation in NRK-52E cells and 1α,25(OH)₂ D₃ can remarkably decrease high glucose-induced lipid accumulation. Western blot showed that 1α,25(OH)₂ D₃ alleviated high glucose-induced upregulation of sterol regulatory element-binding protein-1c (SREBP-1c) and SREBP2, along with their established target genes fatty acid synthase (FASN) and hydroxymethylglutaryl CoA reductases (HMGCR). Overall, these findings suggest that 1α,25(OH)₂ D₃ downregulated the expressions of SREBPs to inhibit high glucose-induced lipid accumulation, which provides new sights into the protective effects of 1α,25(OH)₂ D₃ on diabetic nephropathy.

Crosstalk between the Warburg effect, redox regulation and autophagy induction in tumourigenesis

Tumourigenic tissue uses modified metabolic signalling pathways in order to support hyperproliferation and survival. Cancer-associated aerobic glycolysis resulting in lactic acid production was described nearly 100 years ago. Furthermore, increased reactive oxygen species (ROS) and lactate quantities increase metabolic, survival and proliferation signalling, resulting in increased tumourigenesis. In order to maintain redox balance, the cell possesses innate antioxidant defence systems such as superoxide dismutase, catalase and glutathione. Several stimuli including cells deprived of nutrients or failure of antioxidant systems result in oxidative stress and cell death induction. Among the cell death machinery is autophagy, a compensatory mechanism whereby energy is produced from damaged and/or redundant organelles and proteins, which prevents the accumulation of waste products, thereby maintaining homeostasis. Furthermore, autophagy is maintained by several pathways including phosphoinositol 3 kinases, the mitogen-activated protein kinase family, hypoxia-inducible factor, avian myelocytomatosis viral oncogene homolog and protein kinase receptor-like endoplasmic reticulum kinase. The persistent potential of cancer metabolism, redox regulation and the crosstalk with autophagy in scientific investigation pertains to its ability to uncover essential aspects of tumourigenic transformation. This may result in clinical translational possibilities to exploit tumourigenic oxidative status and autophagy to advance our capabilities to diagnose, monitor and treat cancer.