It can be also consequential to some post-translational modifications, such as phosphorylation of serine 37, which makes the PKM2 nuclear localization signal (NLS) more accessible to importin 5. was present in the cell lines originating from head and neck squamous cell carcinomas: FaDu, Detroit 562 and, especially, Cal27. Very low sensitivity was observed in the colon adenocarcinoma-originating HT-29 cell line, which retained, after exposure to curcumin, a higher levels of lactate production despite decreased glucose consumption. The effects of ethanol were significant. (Pyruvate Kinase M1/2) gene that is located at 15q23. Depending on mutually exclusive inclusion of exons 9 and 10 (both code for 56 amino acids) by splicing machinery, PKM1 and/or PKM2 will be expressed, respectively [2]. The exon 9 containing PKM1 isoform PROTAC MDM2 Degrader-4 is the predominant form in normal adult cells. It exerts its pyruvate kinase activity in the cytoplasm, where it forms constitutively active tetramers. PKM1 presence in the nucleus was shown in several studies [3]. In highly proliferating fetal and cancer cells, PKM2 is the dominant isoform. This isoform is of the utmost importance for the adaptive nature of the Warburg effect. Under physiological conditions, the PROTAC MDM2 Degrader-4 PKM2 isoform can be allosterically activated by fructose-1,6-bisphosphate (FBP) and non-essential amino acid serine, resulting in catalytically active PKM2 tetramers in the cytoplasm [4,5]. Nuclear localization of PKM2 can be a consequence of mutations present in exon 10 (H391Y, G415R, R399E) [6]. It can be also consequential to some post-translational modifications, such as phosphorylation of serine 37, which makes the PKM2 nuclear localization signal (NLS) more accessible to importin 5. PROTAC MDM2 Degrader-4 In the nucleus, PKM2 regulates the activity of genes involved in glucose metabolism to promote the Warburg effect (reviewed in [7]). Phosphorylation of PKM2 has been particularly intensively studied in the field of molecular oncology, primarily as a consequence of commonly increased phosphotyrosine signaling. It was shown that phosphorylation of Y105 plays a critical role in decreasing the pyruvate kinase activity of PKM2, because it cannot be allosterically activated by FBP, nor it can form enzymatically active tetramers [8]. Similarly, formation of functional tetramers can also be inhibited as a consequence of oxidative stress, due to the oxidation of PKM2 cysteine 58 (C358) [9]. Fu et al. reported that hyperactivation of NRF2 (Nuclear Factor (Erythroid-Derived 2)-Like 2), a major transcription regulator of enzymes involved in antioxidative stress response, causes upregulation of Pkm2, its glycosylation and a dramatic increase in its tetrameric form in mice esophagus. High expression of Pkm2 tetramers was accompanied by overexpression YWHAB of genes involved in glycolysis, pentose phosphate pathway (PPP) and glutathione (GSH) metabolism, which is highly dependent on serine [10]. In addition to its importance for maintaining cellular redox homeostasis, the serine biosynthetic pathway is an important alternative source of pyruvate in PKM1/PKM2-deficient cells. Simultaneous silencing of both isoforms in the mouse pancreatic cancer-derived cells (KrasG12D/?; p53?/?) did not affect the level of pyruvate nor did it impact their proliferative potential. Maintaining pyruvate level was shown to be highly dependent on alternative sources, among which the serine biosynthesis pathway was the most prominent one. It was shown to be dependent on the activity of phosphoglycerate dehydrogenase (PHGDH) [11]. In autochthonous mouse models of melanoma and breast PROTAC MDM2 Degrader-4 cancer, PHGDH expression was advantageous for tumor growth as its activity is mandatory for keeping serine level increased in a low exogenous serine condition [12]. Ye et al. have shown that in conditions of high serine demand, and consequent depletion of exogenous serine supply, the cancer cell no longer activates PKM2. Reduced PKM2 activity, in response to serine deprivation, results in an accumulation of glycolytic intermediate 3-phosphoglycerate PROTAC MDM2 Degrader-4 (3-PG), and its.