Tumor pyruvate kinase M2:A promising molecular target of gastrointestinal cancer

Gastrointestinal(GI) cancer is one of the most common causes of cancer-related deaths worldwide.Tumor markers are valuable in detecting post-surgical recurrence or in monitoring response to chemotherapy.Pyruvate kinase isoform M2(PKM2),a glycolytic enzyme catalyzing conversion of phosphoenolpyruvate(PEP) to pyruvate,confers a growth advantage to the tumor cells and enables them to adapt to the tumor microenvironment.In this review,we have summarized current research on the expression and regulation of PKM2 in tumor cells,and its potential role in GI carcinogenesis and progression.Furthermore,we have also discussed the potential of PKM2 as a diagnostic and screening marker,and a therapeutic target in GI cancer.

Celastrol mitigates inflammation in sepsis by inhibiting the PKM2-dependent Warburg effect

Background: Sepsis involves life-threatening organ dysfunction and is caused by a dysregulated host response to infection. No specific therapies against sepsis have been reported. Celastrol(Cel) is a natural anti-inflammatory compound that shows potential against systemic inflammatory diseases. This study aimed to investigate the pharmacological activity and molecular mechanism of Cel in models of endotoxemia and sepsis.Methods: We evaluated the anti-inflammatory efficacy of Cel against endotoxemia and sepsis in mice and macrophage cultures treated with lipopolysaccharide(LPS). We screened for potential protein targets of Cel using activity-based protein profiling(ABPP). Potential targets were validated using biophysical methods such as cellular thermal shift assays(CETSA) and surface plasmon resonance(SPR). Residues involved in Cel binding to target proteins were identified through point mutagenesis, and the functional effects of such binding were explored through gene knockdown.Results: Cel protected mice from lethal endotoxemia and improved their survival with sepsis, and it significantly decreased the levels of pro-inflammatory cytokines in mice and macrophages treated with LPS(P <0.05). Cel bound to Cys424 of pyruvate kinase M2(PKM2), inhibiting the enzyme and thereby suppressing aerobic glycolysis(Warburg effect). Cel also bound to Cys106 in high mobility group box 1(HMGB1) protein, reducing the secretion of inflammatory cytokine interleukin(IL)-1β. Cel bound to the Cys residues in lactate dehydrogenase A(LDHA).Conclusions: Cel inhibits inflammation and the Warburg effect in sepsis via targeting PKM2 and HMGB1 protein.

THE VALUE OF M_2-TYPE PYRUVATE KINASE IMMUNOASSAY IN THE DIAGNOSIS OF HEPATOCARCINOMA

By using Fab'-enzyme labelled immuno absorbent assay (ELISA) with sensitivity of picogram (10-12 g or pg) level, the M-type pyruvate kinase (M-PyK) in plasma was determined in 47 cases of normal healthy adult and 26 cases of hepatocellular carcinoma (HCC) patient. It was found that the upper limits of normal male and female were 1.1 and 1.4 ng/ml (expressed as M2-PyK) respectively. The plasma M-PyK in HCC patients was significant increased to above 5 times of average normal level, the positive rate was about 95%. In 6 cases of subclinical small hepatocarcinoma and 7 cases of HCC patient with normal serum alpha-fetal protein level, the mean plasma M-PyK value was also increased. Whereas the plasma M-PyK level in acute or chronic hepatitis and other benign diseases were normal. After the HCC being resected, the plasma M-PyK returned to normal, but increased again in the cases of recurrent hepatocarcinoma, suggesting that the increased M-PyK in the plasma of HCC patient was criginated from M2-type PyK in HCC tissue. Therefore, plasma M-PyK may become a new micro-level index of hepatocarcinoma.

M2 pyruvate kinase enhances HIV-1 transcription from its long terminal repeat

Both thymocytes and tumor cells express M2 type isoenzyme of pyruvate kinase(M2PK),which is different from R type isoenzyme of pyruvate kinase(RPK)that is expressed in erythrocytes.In this report,the effect of RPK and M2PK on the transcription of human immunodeficiency virus type 1(HIV-1)was tested.The results indicated that M2PK could enhance HIV-1 transcription from its long terminal repeat(LTR)promoter,while RPK did not have such an effect.Specific down-regulation of M2PK could inhibit HIV-1 transcription from its LTR region.Furthermore,it was found that the C terminal region of M2PK is responsible for this effect.Collectively,the cellular factor M2PK that is expressed in thymocytes could facilitate the transcription of HIV-1.

Structural insight into mechanisms for dynamic regulation of PKM2

Pyruvate kinase isoform M2 （PKM2） converts phospho- enolpyruvate （PEP） to pyruvate and plays an important role in cancer metabolism. Here, we show that post- translational modifications and a patient-derived muta- tion regulate pyruvate kinase activity of PKM2 through modulating the conformation of the PKM2 tetramer. We determined crystal structures of human PKM2 mutants and proposed a ＂seesaw＂ model to illustrate confor- mational changes between an inactive T-state and an active R-state tetramers of PKM2. Biochemical and structural analyses demonstrate that PKM2^Y105E （phos- phorylation mimic of Y105） decreases pyruvate kinase activity by inhibiting FBP （fructose 1,6-bisphosphate）- induced R-state formation, and PKM2K^3305Q （acetylation mimic of K305） abolishes the activity by hindering tet- ramer formation. K422R, a patient-derived mutation of PKM2, favors a stable, inactive T-state tetramer because of strong intermolecular interactions. Our study reveals the mechanism for dynamic regulation of PKM2 by post- translational modifications and a patient-derived muta- tion and provides a structural basis for further investi- gation of other modifications and mutations of PKM2 yet to be discovered.