PKM2 gene regulates the behavior of pancreatic cancer cells via mitogen-activated protein kinase pathways

The interplay of p38 MAPK signaling and mitochondrial metabolism, a dynamic target in cancer and pathological contexts

Mitochondria play a crucial role in cellular metabolism and bioenergetics, orchestrating various cellular processes, including energy production, metabolism, adaptation to stress, and redox balance. Besides, mitochondria regulate cellular metabolic homeostasis through coordination with multiple signaling pathways. Importantly, the p38 mitogen-activated protein kinase (MAPK) signaling pathway is a key player in the intricate communication with mitochondria, influencing various functions. This review explores the multifaced interaction between the mitochondria and p38 MAPK signaling and the consequent impact on metabolic alterations. Overall, the p38 MAPK pathway governs the activities of key mitochondrial proteins, which are involved in mitochondrial biogenesis, oxidative phosphorylation, thermogenesis, and iron homeostasis. Additionally, p38 MAPK contributes to the regulation of mitochondrial responses to oxidative stress and apoptosis induced by cancer therapies or natural substances by coordinating with other pathways responsible for energy homeostasis. Therefore, dysregulation of these interconnected pathways can lead to various pathologies characterized by aberrant metabolism. Consequently, gaining a deeper understanding of the interaction between mitochondria and the p38 MAPK pathway and their implications presents exciting forecasts for novel therapeutic interventions in cancer and other disorders characterized by metabolic dysregulation.

The Role of PKM2 in the Regulation of Mitochondrial Function: Focus on Mitochondrial Metabolism, Oxidative Stress, Dynamic, and Apoptosis. PKM2 in Mitochondrial Function

The M2 isoform of pyruvate kinase (PKM2) is one isoform of pyruvate kinase (PK). PKM2 is expressed at high levels during embryonic development and tumor progression and is subject to complex allosteric regulation. PKM2 is a special glycolytic enzyme that regulates the final step of glycolysis; the role of PKM2 in the metabolism, survival, and apoptosis of cancer cells has received increasing attention. Mitochondria are directly or indirectly involved in the regulation of energy metabolism, susceptibility to oxidative stress, and cell death; however, the role of PKM2 in mitochondrial functions remains unclear. Herein, we review the related mechanisms of the role of PKM2 in the regulation of mitochondrial functions from the aspects of metabolism, reactive oxygen species (ROS), dynamic, and apoptosis, which can be highlighted as a target for the clinical management of cardiovascular and metabolic diseases.

The Glycolytic Pathway as a Target for Novel Onco-Immunology Therapies in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDA) is one of the most lethal forms of human cancer, characterized by unrestrained progression, invasiveness and treatment resistance. To date, there are limited curative options, with surgical resection as the only effective strategy, hence the urgent need to discover novel therapies. A platform of onco-immunology targets is represented by molecules that play a role in the reprogrammed cellular metabolism as one hallmark of cancer. Due to the hypoxic tumor microenvironment (TME), PDA cells display an altered glucose metabolism-resulting in its increased uptake-and a higher glycolytic rate, which leads to lactate accumulation and them acting as fuel for cancer cells. The consequent acidification of the TME results in immunosuppression, which impairs the antitumor immunity. This review analyzes the genetic background and the emerging glycolytic enzymes that are involved in tumor progression, development and metastasis, and how this represents feasible therapeutic targets to counteract PDA. In particular, as the overexpressed or mutated glycolytic enzymes stimulate both humoral and cellular immune responses, we will discuss their possible exploitation as immunological targets in anti-PDA therapeutic strategies.

Protein kinase function of pyruvate kinase M2 and cancer

Pyruvate kinase is a terminal enzyme in the glycolytic pathway, where it catalyzes the conversion of phosphoenolpyruvate to pyruvate and production of ATP via substrate level phosphorylation. PKM2 is one of four isoforms of pyruvate kinase and is widely expressed in many types of tumors and associated with tumorigenesis. In addition to pyruvate kinase activity involving the metabolic pathway, increasing evidence demonstrates that PKM2 exerts a non-metabolic function in cancers. PKM2 has been shown to be translocated into nucleus, where it serves as a protein kinase to phosphorylate various protein targets and contribute to multiple physiopathological processes. We discuss the nuclear localization of PKM2, its protein kinase function and association with cancers, and regulation of PKM2 activity.

Cutting off the fuel supply to calcium pumps in pancreatic cancer cells: role of pyruvate kinase-M2 (PKM2)

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) has poor survival and treatment options. PDAC cells shift their metabolism towards glycolysis, which fuels the plasma membrane calcium pump (PMCA), thereby preventing Ca2+-dependent cell death. The ATP-generating pyruvate kinase-M2 (PKM2) is oncogenic and overexpressed in PDAC. This study investigated the PKM2-derived ATP supply to the PMCA as a potential therapeutic locus.

METHODS

PDAC cell growth, migration and death were assessed by using sulforhodamine-B/tetrazolium-based assays, gap closure assay and poly-ADP ribose polymerase (PARP1) cleavage, respectively. Cellular ATP and metabolism were assessed using luciferase/fluorescent-based assays and the Seahorse XFe96 analyzer, respectively. Cell surface biotinylation identified membrane-associated proteins. Fura-2 imaging was used to assess cytosolic Ca2+ overload and in situ Ca2+ clearance. PKM2 knockdown was achieved using siRNA.

RESULTS

The PKM2 inhibitor (shikonin) reduced PDAC cell proliferation, cell migration and induced cell death. This was due to inhibition of glycolysis, ATP depletion, inhibition of PMCA and cytotoxic Ca2+ overload. PKM2 associates with plasma membrane proteins providing a privileged ATP supply to the PMCA. PKM2 knockdown reduced PMCA activity and reduced the sensitivity of shikonin-induced cell death.

CONCLUSIONS

Cutting off the PKM2-derived ATP supply to the PMCA represents a novel therapeutic strategy for the treatment of PDAC.

Cysteine catabolism and the serine biosynthesis pathway support pyruvate production during pyruvate kinase knockdown in pancreatic cancer cells

Background

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with limited treatment options. Pyruvate kinase, especially the M2 isoform (PKM2), is highly expressed in PDAC cells, but its role in pancreatic cancer remains controversial. To investigate the role of pyruvate kinase in pancreatic cancer, we knocked down PKM2 individually as well as both PKM1 and PKM2 concurrently (PKM1/2) in cell lines derived from a Kras^G12D/-; p53^-/- pancreatic mouse model.

Methods

We used liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine metabolic profiles of wildtype and PKM1/2 knockdown PDAC cells. We further used stable isotope-labeled metabolic precursors and LC-MS/MS to determine metabolic pathways upregulated in PKM1/2 knockdown cells. We then targeted metabolic pathways upregulated in PKM1/2 knockdown cells using CRISPR/Cas9 gene editing technology.

Results

PDAC cells are able to proliferate and continue to produce pyruvate despite PKM1/2 knockdown. The serine biosynthesis pathway partially contributed to pyruvate production during PKM1/2 knockdown: knockout of phosphoglycerate dehydrogenase in this pathway decreased pyruvate production from glucose. In addition, cysteine catabolism generated ~ 20% of intracellular pyruvate in PDAC cells. Other potential sources of pyruvate include the sialic acid pathway and catabolism of glutamine, serine, tryptophan, and threonine. However, these sources did not provide significant levels of pyruvate in PKM1/2 knockdown cells.

Conclusion

PKM1/2 knockdown does not impact the proliferation of pancreatic cancer cells. The serine biosynthesis pathway supports conversion of glucose to pyruvate during pyruvate kinase knockdown. However, direct conversion of serine to pyruvate was not observed during PKM1/2 knockdown. Investigating several alternative sources of pyruvate identified cysteine catabolism for pyruvate production during PKM1/2 knockdown. Surprisingly, we find that a large percentage of intracellular pyruvate comes from cysteine. Our results highlight the ability of PDAC cells to adaptively rewire their metabolic pathways during knockdown of a key metabolic enzyme.

PKM2: A Potential Regulator of Rheumatoid Arthritis via Glycolytic and Non-Glycolytic Pathways

Immunometabolism provides a new perspective on the pathogenesis of rheumatoid arthritis (RA). In recent years, there have been investigations focusing on the role of intracellular glucose metabolism in the pathogenesis of RA. Previous studies have shown that glycolysis of synovial tissue is increased in RA patients, while glycolysis inhibitors can significantly inhibit synovitis. Pyruvate kinase (PK) is a key enzyme in glycolysis, catalyzing the final rate-limiting step in the process. An isoform of PK, PKM2, provides favorable conditions for the survival of tumor cells via its glycolytic or non-glycolytic functions and has become a potential therapeutic target in tumors. RA synovium has the characteristic of tumor-like growth, and, moreover, increased expression of PKM2 was identified in the synovial tissue of RA patients in recent studies, indicating the underlying role of PKM2 in RA. PKM2 has potential value as a new therapeutic target or biomarker for RA, but its exact role in RA remains unclear. In this review, the properties of PKM2 and existing research concerning PKM2 and RA are thoroughly reviewed and summarized, and the possible role and mechanism of PKM2 in RA are discussed.

PKM2 is not required for pancreatic ductal adenocarcinoma

BACKGROUND

While most cancer cells preferentially express the M2 isoform of the glycolytic enzyme pyruvate kinase (PKM2), PKM2 is dispensable for tumor development in several mouse cancer models. PKM2 is expressed in human pancreatic cancer, and there have been conflicting reports on the association of PKM2 expression and pancreatic cancer patient survival, but whether PKM2 is required for pancreatic cancer progression is unknown. To investigate the role of PKM2 in pancreatic cancer, we used a conditional allele to delete PKM2 in a mouse model of pancreatic ductal adenocarcinoma (PDAC).

RESULTS

PDAC tumors were initiated in LSL-Kras G12D/+ ;Trp53 flox/flox ;Pdx-1-Cre (KP-/-C) mice harboring a conditional Pkm2 allele. Immunohistochemical analysis showed PKM2 expression in wild-type tumors and loss of PKM2 expression in tumors from Pkm2 conditional mice. PKM2 deletion had no effect on overall survival or tumor size. Loss of PKM2 resulted in pyruvate kinase M1 (PKM1) expression, but did not affect the number of proliferating cells. These findings are consistent with results in other cancer models.

CONCLUSIONS

PKM2 is not required for initiation or growth of PDAC tumors arising in the KP-/-C pancreatic cancer model. These findings suggest that, in this mouse PDAC model, PKM2 expression is not required for pancreatic tumor formation or progression.

The responsively decreased PKM2 facilitates the survival of pancreatic cancer cells in hypoglucose

Cancer cells predominantly produce energy at a high rate of glycolysis even in aerobic environment. It is termed as Warburg effect and is necessary for the tumorigenesis. Studies showed pyruvate kinase M2 (PKM2), a key regulator of the Warburg effect, is overexpressed and involved in numerous cancers. However, the expression and function of PKM2 in pancreatic cancer (PC) remain undefined. Our results showed that PKM2 is overexpressed in the PC tissue compared to the peritumoral tissue. Unexpected, the downregulation of PKM2 did not affect the proliferation, invasion, and chemoresistance of PC cells. Since pancreatic cancer is a hypovascular tumor with comparably insufficient energy supply, we further investigate the relationship between PKM2 and hypoglucose. Interestingly, we further discovered that decreased expression of PKM2 was detected in PC samples with lower microvessel density as well as in PC cells treated with hypoglucose condition (0.5 mM). Furthermore, the downregulation of PKM2 facilitated, while the upregulation of PKM2 inhibited, PC cells survival during hypoglucose. We further revealed that the repressed PKM2 induced autophagy, high NADPH/NADP ratio, and biomacromolecule production, but reduced ROS accumulation. Moreover, AMPKα1 knockdown repressed the autophagy and survival of PC cells during hypoglucose, which were promoted by PKM2 knockdown. Collectively, our study indicates that decreased PKM2 diverts glucose metabolism to biomacromolecule accumulation and antioxidants generation during glucose deprivation. This metabolism alteration elevates AMPKα1-dependent autophagy, which facilitates PC cell survival during glucose deprivation. Therefore, functions of PKM2 are complicated and cannot be defined as oversimplified promoter or inhibitor in PC.

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.

PACE4 regulates apoptosis in human pancreatic cancer Panc‑1 cells via the mitochondrial signaling pathway

Previous studies have demonstrated the overexpression of paired basic amino acid cleaving enzyme 4 (PACE4) mRNA in prostate cancer tissues. This overexpression is correlated with higher circulating protein levels in certain patients, however, the role of PACE4 in apoptosis and the potential molecular mechanisms of pancreatic cancer remain to be elucidated. The aim of the present study was to investigate the effect and potential molecular mechanisms of PACE4 on apoptosis in the Panc‑1 pancreatic cancer cell line. Cell proliferation was assessed using a Cell Counting Kit‑8 assay. Apoptotic nuclear shrinkage was monitored using Hoechst 33258 staining. Caspase‑3/7 activities were measured using a colorimetric caspase‑glo 3/7 assay. Alterations in protein expression were monitored using Western blot analysis. The results indicated that PACE4 small interfering (si)RNA inhibited cell proliferation and activated caspase‑3/7 activities. In addition, PACE4 siRNA significantly increased apoptosis via the activation of caspase‑3 and the downregulation of anti‑apoptotic proteins, X‑linked inhibitor of apoptosis protein and phosphorylated‑Akt. In addition, the results showed deregulation of the B cell lymphoma‑2 (Bcl‑2)-associated X protein/Bcl‑2 ratio which led to the release of cytochrome c following PACE4 siRNA transfection. In conclusion, PACE4 siRNA may exert antitumor activity through the mitochondrial pathway and is expected to be a promising therapeutic strategy for the treatment of pancreatic cancer.

Pyruvate Kinase M2 and Lactate Dehydrogenase A Are Overexpressed in Pancreatic Cancer and Correlate with Poor Outcome

Pancreatic cancer has a 5-year survival rate of less than 4%. Despite advances in diagnostic technology, pancreatic cancer continues to be diagnosed at a late and incurable stage. Accurate biomarkers for early diagnosis and to predict treatment response are urgently needed. Since alteration of glucose metabolism is one of the hallmarks of cancer cells, we proposed that pyruvate kinase type M2 (M2PK) and lactate dehydrogenase A (LDHA) enzymes could represent novel diagnostic markers and potential therapeutic targets in pancreatic cancer. In 266 tissue sections from normal pancreas, pancreatic cystic neoplasms, pancreatic intraepithelial neoplasia (PanIN) and cancer, we evaluated the expression of PKM2, LDHA, Ki-67 and CD8+ by immunohistochemistry and correlated these markers with clinicopathological characteristics and patient survival. PKM2 and LDHA expression was also assessed by Western blot in 10 human pancreatic cancer cell lines. PKM2 expression increased progressively from cyst through PanIN to cancer, whereas LDHA was overexpressed throughout the carcinogenic process. All but one cell line showed high expression of both proteins. Patients with strong PKM2 and LDHA expression had significantly worse survival than those with weak PKM2 and/or LDHA expression (7.0 months vs. 27.9 months, respectively, p = 0.003, log rank test). The expression of both PKM2 and LDHA correlated directly with Ki-67 expression, and inversely with intratumoral CD8+ cell count. PKM2 was significantly overexpressed in poorly differentiated tumours and both PKM2 and LDHA were overexpressed in larger tumours. Multivariable analysis showed that combined expression of PKM2 and LDHA was an independent poor prognostic marker for survival. In conclusion, our results demonstrate a high expression pattern of two major glycolytic enzymes during pancreatic carcinogenesis, with increased expression in aggressive tumours and a significant adverse effect on survival.

PKM2 Promotes Cell Survival and Invasion Under Metabolic Stress by Enhancing Warburg Effect in Pancreatic Ductal Adenocarcinoma

BACKGROUND

Pyruvate kinase isoenzyme M2 (PKM2) is an essential enzyme involved in the regulation of aerobic glycolysis in cancer cells and promotes the translation between glycolytic flux and biosynthesis of cellular building blocks.

AIM

Our present study aims to explore the expression pattern and underlying cellular functions of PKM2 in pancreatic ductal adenocarcinoma (PDAC) under metabolic stress.

METHODS

Oncomine database and a tissue microarray (n = 90) were used to investigate the expression pattern of PKM2 and its clinicopathological findings. In vitro proliferation, apoptosis and invasion assays were used to determine the role and related mechanism of PKM2 in PDAC.

RESULTS

Data from Oncomine database and our tissue microarray show that PKM2 is significantly elevated in PDAC specimens compared with the corresponding normal tissues. Kaplan-Meier survival analysis shows that higher expression of PKM2 is closely correlated with a poor prognosis of patients with PDAC. Under metabolic stress, suppression of PKM2 expression in PANC-1 and AsPC-1 cells results in decreased cell survival, increased caspase-3/7 activity, and reduced invasive potential, and these effects can be reversed by reintroduction of PKM2. Furthermore, sh-PKM2 cells show a significant decreased Warburg effect compared with sh-Ctrl cells as demonstrated by reduced glucose consumption and lactate production. Treatment with 2-deoxy-D-glucose, a glycolysis inhibitor, completely blocks the influences of PKM2 on cell survival and invasion.

CONCLUSIONS

Our study reveals that silencing of PKM2 exhibits a tumor-suppressive role through altered Warburg effect and suggests that targeting PKM2 might serve as a potential therapeutic target for PDAC.

Microarray expression profile analysis of long non-coding RNAs in pancreatic ductal adenocarcinoma

Long non-coding RNA (lncRNA) is a variety of the human transcriptome that does not code for proteins and plays an important role in the development and progression of multiple solid malignant tumors. However, the roles of lncRNAs in the development of pancreatic ductal adenocarcinoma (PDAC) remain unknown. In this study, we investigated the expression patterns of lncRNAs in three PDAC tumor samples (T) relative to those of matched adjacent non-tumor tissues (N) via a microarray with 30,586 lncRNA probes and 26,109 mRNA probes. The lncRNA microarray revealed 27,279 lncRNAs in PDAC samples, of which 2,331 were significantly upregulated (P<0.05; T/N>2.0) and 1,641 were downregulated (P<0.05; N/T>2.0) compared with matched adjacent non-tumor samples. In addition, 19,995 mRNAs were detected, of which 1,676 were significantly upregulated (P<0.05; T/N>2.0) and 1,981 were downregulated (P<0.05; N/T>2.0). Pathway analysis indicated that 41 pathways corresponded to upregulated transcripts and 25 pathways corresponded to downregulated transcripts (P-value cut-off is 0.05). Gene ontology (GO) analysis showed that the highest enriched GOs targeted by upregulated and downregulated transcripts were tissue homeostasis. The validation results from quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis and microarray analysis were consistent. Furthermore, the expression level of long intergenic non-coding RNA HOTAIRM1 was upregulated in 12 PDAC tissues samples compared with matched adjacent non-tumor samples by qRT-PCR. The results showed that the lncRNA and mRNA expression profiles differed significantly between the PDAC tissues and their adjacent non-tumor tissues, and the revelation of an association between HOTAIRM1 expression and PDAC is especially noteworthy. These findings may provide new potential molecular markers for diagnosis and treatment of PDAC.

Pyruvate kinase isoform M2 (PKM2) participates in multiple myeloma cell proliferation, adhesion and chemoresistance

Cell adhesion mediated drug resistance (CAM-DR) remains the major barrier in human multiple myeloma (MM) therapy. In the present study, we aimed at investigating the role of pyruvate kinase isoform M2 (PKM2) in MM CAM-DR. We determined that PKM2 expression was positively correlated with cell proliferation and knockdown of PKM2 contributed to the increased cell adhesion rate in MM. The enhancement in the adhesion of MM cells to fibronectin or the bone marrow stroma cell line HS-5 cells translated to an increased CAM-DR phenotype. Importantly, we showed that this CAM-DR phenotype was correlated with the phosphorylation of Akt and ERK in MM cells. Taken together, our data shed new light on the molecular mechanism of CAM-DR in MM, and targeting PKM2 may be a novel therapeutic approach for improving the effectiveness of chemotherapy in MM.