Pyruvate Kinase M2 Knockdown Research Articles

High glucose enhances the metastatic potential of tongue squamous cell carcinoma via the PKM2 pathway.

Previous evidence has indicated an increased cancer risk in individuals with diabetes mellitus (DM). The aim of this study was to investigate the relationship between DM (high glucose) and tongue squamous cell carcinoma (TSCC) and how high glucose mediated the metastatic potential of TSCC. The relationship between DM and TSCC was assessed in a retrospective study. The role and its mechanism of high glucose on the proliferation, metastatic potential of TSCC were investigated in vitro and in vivo. The prevalence rate of DM in patients with TSCC was 12.84%, which was significantly higher than that (9.7%) in the general population in China. Although no significant difference was observed in the overall survival (OS) rate, TSCC patients with DM have a 1.38-fold increase in relative risk affecting 5-year OS compared to patients without DM. High glucose enhanced the TSCC cell proliferation, migration, invasion and upregulated PKM2 (pyruvate kinase M2) expression. Whereas, these effect was abolished after knockdown of PKM2 in TSCC cells. High glucose promoted tumour growth and lung metastasis of TSCC in a DM animal model. Our results confirm DM as a risk factor for the development of TSCC. High glucose enhances the metastatic potential of TSCC through stimulation of the PKM2 pathway.

Knockdown of pyruvate kinase type M2 suppresses tumor survival and invasion in osteosarcoma cells both in vitro and in vivo

Osteosarcoma (OS) is the mostly diagnosed primary bone malignancy. Emerging evidence indicates that the activity of pyruvate kinase M2 (PKM2) isoform is crucial for the survival of tumor cells. In the present study, the effect of PKM2 knockdown on the proliferation and migration of OS cells were assessed both in vitro and in vivo. Small hairpin RNA (shRNA) technology were employed to suppress the expression of PKM2 in MG-63 and Saos-2 cell lines. In vitro, shRNA-mediated knockdown of PKM2 efficiently inhibited cell proliferation, and induced G1 cell cycle arrest and apoptosis in both cell lines, which was associated with decreased expressions of cyclin D1 and Bcl-2 as well as increased expressions of Bax, cleaved-caspase-3, and cleaved-PARP. The invasion and migration potential of OS cell lines were also inhibited by PKM2 knockdown through the regulating effect of PKM2 on MMP-2 and VEGF signaling. In vivo, knockdown of PKM2 decelerated tumor growth rate and induced structure deterioration in tumor tissues. The current study for the first time showed that the activity of PKM2 was indispensable for the development and metastasis of OS, thereby providing the basic information for the future development of PKM2-based anti-OS therapies.

Pyruvate kinase M2 deregulation enhances the metastatic potential of tongue squamous cell carcinoma.

Pyruvate kinase M2 (PKM2) has been verified to correlate with the prognosis of many types of cancer. However, its role in the development and metastasis of tongue squamous cell carcinoma (TSCC) remains unclear. The immunohistochemistry (IHC) results confirmed that PKM2 is overexpressed in patients with TSCC. PKM2 up-regulation was related to lymph node metastasis and associated with reduced overall survival. According to the microarray analysis and Western blots, PKM2 expression was up-regulated in TSCC cells with enhanced metastatic potential. PKM2 knockdown inhibited cell migration and invasion, reduced SOD2 (manganese superoxide dismutase) activity and the intracellular H2O2 level, and inhibited tumour growth and lung metastasis in vivo. PKM2 overexpression promoted cell migration and invasion, and increased SOD2 activity and the intracellular H2O2 level. Moreover, miR-138 directly targeted PKM2 and inhibited PKM2 expression. Thus, PKM2 deregulation plays an important role in TSCC and may serve as a biomarker of metastatic potential or as a therapeutic target in patients with TSCC. PKM2, a miR-138 target gene, enhances the metastatic potential of TSCC through the SOD2-H2O2 pathway.

PKM2 promotes cell migration and inhibits autophagy by mediating PI3K/AKT activation and contributes to the malignant development of gastric cancer

Pyruvate kinase M2 (PKM2) is a key kinase of glycolysis and is characteristic of all proliferating cells. The role of PKM2 in gastric cancer (GC) is still ambiguous and yet to be determined. To better understand the role of PKM2 in both the migration and invasion of GC, we measured the expression of PKM2 in GC cell lines using qRT-PCR and western blot. The prognostic value of PKM2 was analyzed by Immunohistochemistry in a cohort containing 88 GC patients. PKM2 was knocked down by the short hairpin RNA plasmid vector in NCI-N87 and BGC-823 cells, and the biological behavior and downstream signaling pathways were also investigated in vitro. Subcutaneous xenografts and pulmonary metastases models were constructed in nude mice to compare the differences in tumorgenesis and metastasis after Knockdown of PKM2. Our results obtained from in vitro cell biological behavior, in vivo tumorigenicity studies, and primary GC samples revealed an oncogenic role for PKM2 in GC. Furthermore, for those GC patients who received radical resection, PKM2 might serve as a novel prognostic biomarker and target which would allow for a brand new treatment strategy for GC in the clinical settings.

Pyruvate kinase M2 interacts with mammalian sterile 20-like kinase 1 and inhibits tamoxifen-induced apoptosis in human breast cancer cells.

Tamoxifen has been reported to be associated with antagonism of estrogen-mediated cell growth signaling and activation of estrogen receptor-independent apoptosis events. It has been demonstrated that mammalian sterile 20-like kinase 1 is a direct target of Caspases to amplify the apoptotic signaling pathway. Here, we presented that breast cancer MCF-7 and SKBR3 cells under treatment with 4-hydroxytamoxifen displayed decreased level of pyruvate kinase M2. Western blot results also showed that 4-hydroxytamoxifen induced the activity of pro-apoptotic protein Caspase-3 in MCF-7 and SKBR3 cells, as evidenced by the cleavage of mammalian sterile 20-like kinase 1 substrate in a dose-dependent manner. Co-immunoprecipitation and immunofluorescence experiments were performed to clarify the relationship between pyruvate kinase M2 and mammalian sterile 20-like kinase 1. The results indicated that mammalian sterile 20-like kinase 1 was associated with pyruvate kinase M2 in cultured mammalian cells, and the interaction between mammalian sterile 20-like kinase 1 and pyruvate kinase M2 was decreased in response to 4-hydroxytamoxifen treatment. In addition, knockdown of pyruvate kinase M2 upregulated the level of cleaved Caspase-3 and subsequently facilitated the nuclear translocation of mammalian sterile 20-like kinase 1. Our data further supplemented the extensive functions of pyruvate kinase M2 in mediating breast cancer cell viability by substantially abating the mammalian sterile 20-like kinase 1-mediated apoptosis. In summary, our results identified that mammalian sterile 20-like kinase 1 is a novel downstream target of pyruvate kinase M2, and knockdown of pyruvate kinase M2 contributes apoptosis via promoting nuclear translocation of mammalian sterile 20-like kinase 1 by enhancing Caspase-3-dependent cleavage.

Inhibition of Proliferation, Migration, and Invasion by Knockdown of Pyruvate Kinase-M2 (PKM2) in Ovarian Cancer SKOV3 and OVCAR3 Cells.

Pyruvate kinase (PK) is a key enzyme in the process of glycolysis, catalyzing phosphoenolpyruvate (PEP) into pyruvate. Currently, PK isozyme type M2 (PKM2), one subtype of PK, has been proposed as a new tumor marker with high expression in various tumor tissues. Here we aimed to explore the effects of siRNA-PKM2 on ovarian carcinoma (OC) cell lines SKOV3 and OVCAR3, in which PKM2 was notably expressed. PKM2 gene interference lentivirus vectors were built by miRNA transfection assay. siRNA-PKM2-transfected SKOV3 and OVCAR3 cells were evaluated for cell proliferation, cell cycle distribution, cell apoptosis, cell migration, and invasion in this study. In addition, the expression levels of several tumor-related genes were measured using real-time PCR and Western blot. Results showed that siRNA-PKM2 markedly inhibited cell proliferation, induced apoptosis, and caused cell cycle arrest at the G0/G1 phase. Cell migration and invasion were significantly suppressed by siRNA-PKM2. Furthermore, the tumor-related genes caspase 7, Bad, and E-cadherin were upregulated, while MMP2, HIF1α, VEGF, and MMP9 were depressed by siRNA-PKM2. The function of siRNA-PKM2 on the biological behavior of OC cells indicated that PKM2 may also be a target for treatment of OC.

Abstract 1567: Prostate cancer-derived exosomes alter the metabolic microenvironment of bone marrow pre-metastatic niche through PKM2 to promote bone metastasis

Abstract Tumor-derived exosomes are emerging mediators of tumor progression. We explored the role of prostate cancer (PCa)-derived exosomes (Ex) in PCa bone metastasis. Systemic pre-treatment of mice with PCa-Ex increased PCa tumor growth in bone, this was associated with increased early PCa cell seeding into the bone marrow. PCa-Ex had no direct impact on PCa growth or invasive ability in vitro; whereas, conditioned-media (CM) from PCa-Ex-treated stromal cells increased PCa cell growth, invasion and epithelial mesenchymal transition (EMT). PCa-Ex preferentially targeted bone marrow versus lung or liver stroma when injected IV. Proteomic analysis of PCa-Ex-treated cells revealed that PCa-Ex increased pyruvate kinase M2 (PKM2) protein expression in both ST2 stromal cells and primary bone marrow stromal cells, although PKM2 mRNA expression was not altered. PKM2 protein expression correlated with aggressiveness of PCa cell lines and was highest in serum of PCa patients with metastases compared to those with primary tumors. PCa-Ex induced both autophagy and β-hydroxybutarate (BHB) production from stromal cells. Knockdown of PKM2 in PCa cells resulted in production of PCa-Ex with low PKM2. The low PKM2 PCa-Ex had diminished ability to induce PCa cell growth, autophagy and BHB production. IV PCa-Ex and orthotopic tumors increased bone marrow BHB levels. PCa-Ex treatment of stromal cells induced the CM to (1) increase in oxygen consumption rate (OCR) by 80%; (2) extracellular acidification rate (ECAR) by 25%; and (3) increase ATP production in PCa cells. BHB induced OCR, but not ECAR in a dose responsive fashion. BHB administration induced a dose-responsive increase in intratibial tumor growth in mice. Our experiments indicate that primary tumor PCa-Ex can target the bone marrow microenvironment and educate stromal cells to promote PCa progression through increasing PKM2 expression in stromal cells resulting in ketone production that supports metastatic growth. Overall this demonstrates that primary tumor exosomes modulate the metabolic status of the distant pre-metastatic niche to promote metastasis. Citation Format: Jinlu Dai, Yi Lu, Jian Zhang, Evan Keller. Prostate cancer-derived exosomes alter the metabolic microenvironment of bone marrow pre-metastatic niche through PKM2 to promote bone metastasis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1567.

JMJD8 Regulates Angiogenic Sprouting and Cellular Metabolism by Interacting With Pyruvate Kinase M2 in Endothelial Cells.

Jumonji C (JmjC) domain-containing proteins modify histone and nonhistone proteins thereby controlling cellular functions. However, the role of JmjC proteins in angiogenesis is largely unknown. Here, we characterize the expression of JmjC domain-containing proteins after inducing endothelial differentiation of murine embryonic stem cells and study the function of JmjC domain-only proteins in endothelial cell (EC) functions. We identified a large number of JmjC domain-containing proteins regulated by endothelial differentiation of murine embryonic stem cells. Among the family of JmjC domain-only proteins, Jmjd8 was significantly upregulated on endothelial differentiation. Knockdown of Jmjd8 in ECs significantly decreased in vitro network formation and sprouting in the spheroid assay. JMJD8 is exclusively detectable in the cytoplasm, excluding a function as a histone-modifying enzyme. Mass spectrometry analysis revealed JMJD8-interacting proteins with known functions in cellular metabolism like pyruvate kinase M2. Accordingly, knockdown of pyruvate kinase M2 in human umbilical vein ECs decreased endothelial sprouting in the spheroid assay. Knockdown of JMJD8 caused a reduction of EC metabolism as measured by Seahorse Bioscience extracellular flux analysis. Conversely, overexpression of JMJD8 enhanced cellular oxygen consumption rate of ECs, reflecting an increased mitochondrial respiration. Jmjd8 is upregulated during endothelial differentiation and regulates endothelial sprouting and metabolism by interacting with pyruvate kinase M2.

Overexpression of pyruvate kinase M2 associates with aggressive clinicopathological features and unfavorable prognosis in oral squamous cell carcinoma

Abnormal glucose metabolism mediated by pyruvate kinase M2 (PKM2) fuels cancer overgrowth and propagation. However, its expression and oncogenic roles in in oral squamous cell carcinoma (OSCC) remains incompletely known. Here, we aimed to investigate the expression of PKM2, its prognostic values and oncogenic functions using 7,12-dimethyl-1,2-bezan-tracene (DMBA)-induced hamster buccal pouch SCC model, primary OSCC specimens as well as in vitro cellular assays. We found that in DMBA-induced OSCC model, negative PKM2 expression was commonly observed in normal epithelial, while more PKM2 abundance was detected in hyperplasia, dysplasia and SCC. Overexpression of PKM2 in a major fraction of OSCC significantly associated with tumor size (P = 0.027), cervical node metastasis (P = 0.004) and clinical stages (P = 0.000). Patients with increased PKM2 had remarkably reduced overall and disease-free survival. Multivariate survival analysis further revealed that PKM served as a critical independent prognostic factor for patients' overall survival. Furthermore, impaired cell proliferation and migration, and reduced apoptosis were detected upon PKM2 knockdown in HN4 and HN12 cells. Taken together, our findings reveal that PKM2 is critically involved in OSCC initiation and progression probably by promoting cell proliferation and migration as well as reducing apoptosis. Its overexpression correlates with aggressive clinicopathological features and poor patients' outcome.

Pyruvate kinase M2 prevents apoptosis via modulating Bim stability and associates with poor outcome in hepatocellular carcinoma.

Pyruvate kinase M2 (PKM2) contributes to the Warburg effect, a hallmark of cancer. We showed that PKM2 levels were correlated with overall survival (hazard ration = 1.675, 95% confidence interval: 1.389-2.019, P < 0.001) and disease-free survival (hazard ration = 1.573, 95% confidence interval: 1.214-2.038, P < 0.001) in a cohort of 490 patients with HCC. The correlations were further validated in an independent cohort of 148 HCC patients. Multivariate analyses revealed that PKM2 was an independent indicator of poor outcome in HCC. The knockdown of PKM2 in HCC cells inhibited cell proliferation and induced apoptosis in vitro and in vivo. Bim siRNA markedly abolished the PKM2-depletion-induced apoptosis. PKM2 depletion decreased the degradation of Bim. In clinical samples, PKM2 expression was reversely correlated with Bim expression. Combination of PKM2 and Bim levels had the best prognostic significance. We suggest that PKM2 serves as a promising biomarker for poor prognosis of patients with HCC and its knockdown induces HCC apoptosis by stabilizing Bim.

Switching of pyruvate kinase isoform L to M2 promotes metabolic reprogramming in hepatocarcinogenesis.

Hepatocellular carcinoma (HCC) is an aggressive tumor, with a high mortality rate due to late symptom presentation and frequent tumor recurrences and metastasis. It is also a rapidly growing tumor supported by different metabolic mechanisms; nevertheless, the biological and molecular mechanisms involved in the metabolic reprogramming in HCC are unclear. In this study, we found that pyruvate kinase M2 (PKM2) was frequently over-expressed in human HCCs and its over-expression was associated with aggressive clinicopathological features and poor prognosis of HCC patients. Furthermore, knockdown of PKM2 suppressed aerobic glycolysis and cell proliferation in HCC cell lines in vitro. Importantly, knockdown of PKM2 hampered HCC growth in both subcutaneous injection and orthotopic liver implantation models, and reduced lung metastasis in vivo. Of significance, PKM2 over-expression in human HCCs was associated with a down-regulation of a liver-specific microRNA, miR-122. We further showed that miR-122 interacted with the 3UTR of the PKM2 gene. Re-expression of miR-122 in HCC cell lines reduced PKM2 expression, decreased glucose uptake in vitro, and suppressed HCC tumor growth in vivo. Our clinical data and functional studies have revealed a novel biological mechanism involved in HCC metabolic reprogramming.

PKM2 regulates the Warburg effect and promotes HMGB1 release in sepsis.

Increasing evidence suggests the important role of metabolic reprogramming in the regulation of the innate inflammatory response, but the underlying mechanism remains unclear. Here, we provide evidence to support a novel role for the pyruvate kinase M2 (PKM2)-mediated Warburg effect, namely aerobic glycolysis, in the regulation of high mobility group box 1 (HMGB1) release. PKM2 interacts with hypoxia-inducible factor 1α (HIF1α) and activates the HIF-1α-dependent transcription of enzymes necessary for aerobic glycolysis in macrophages. Knockdown of PKM2, HIF1α, and glycolysis-related genes uniformly decreases lactate production and HMGB1 release. Similarly, a potential PKM2 inhibitor, shikonin, reduces serum lactate and HMGB1 levels and protects mice from lethal endotoxemia and sepsis. Collectively, these findings shed light on a novel mechanism for metabolic control of inflammation by regulating HMGB1 release and highlight the importance of targeting aerobic glycolysis in the treatment of sepsis and other inflammatory diseases.

Pyruvate kinase M2 regulates apoptosis of intestinal epithelial cells in Crohn's disease.

Pyruvate kinase M2 (PKM2), a key glycolytic enzyme, is involved in multiple cellular processes including apoptosis. Recently increased fecal PKM2 has been found in Crohn's disease (CD), but little is known regarding its function in the pathophysiology of the disease. The intestinal expression of PKM2 and its involvement in CD was investigated. Pyruvate kinase M2 expression in mucosal biopsies from patients with CD and normal controls was detected by immunohistochemistry. A murine model of colitis induced by trinitrobenzenesulphonic acid (TNBS) was established and expression of PKM2, B cell lymphoma-extra large (Bcl-xl), active caspase-3 as well as cleaved poly (ADP-ribose) polymerase (PARP) was examined for association of PKM2 with intestinal epithelial cell (IEC) apoptosis. Furthermore, we treated human IEC line HT-29 by tumor necrosis factor-α (TNF-α) and used RNA interference to analyze the role of PKM2 in IEC apoptosis. Intestinal expression of PKM2 was higher in patients with CD compared with normal controls mainly locating in IECs. In TNBS-induced colitis, up-regulation of PKM2 was accompanied by the elevated expression of Bcl-xl, active caspase-3, and cleaved PARP. PKM2 was co-localized with active caspase-3 in IECs marked by E-cadherin, suggesting its role in IEC apoptosis. Expression of PKM2 and Bcl-xl in TNF-α-induced HT-29 cells was increased, while TNF-α had no effect on cellular localization of PKM2. Furthermore, knockdown of PKM2 by siRNA could inhibit expression of Bcl-xl but enhance apoptosis in TNF-α-treated HT-29 cells. The up-regulation of PKM2 might protect IECs against apoptosis possibly through Bcl-xl in CD, indicating its important role in the pathophysiology of CD.

Proteome Profiling of Mitotic Clonal Expansion during 3T3-L1 Adipocyte Differentiation Using iTRAQ-2DLC-MS/MS

Mitotic clonal expansion (MCE) is one of the important events taking place at the early stage during 3T3-L1 adipocyte differentiation. To investigate the mechanism underlying this process, we carried out a temporal proteomic analysis to profile the dynamic changes in MCE. Using 8-plex-iTRAQ-2DLC-MS/MS analysis, 3152 proteins were quantified during the initial 28 h of 3T3-L1 adipogenesis. Functional analysis was performed on 595 proteins with maximum or minimum quantities at 20 h of adipogenic induction that were potentially involved in MCE, which identified PI3K/AKT/mTOR as the most relevant pathway. Among the 595 proteins, PKM2 (Pyruvate kinase M2), a patterned protein identified as a potential target gene of C/EBPβ in our previous work, was selected for further investigation. Network analysis suggested positive correlations among C/EBPβ, PIN1, and PKM2, which may be related with the PI3K-AKT pathway. Knockdown of PKM2 with siRNA inhibited both MCE and adipocyte differentiation of 3T3-L1 cells. Moreover, PKM2 was down-regulated at both the mRNA level and the protein level upon the knockdown of C/EBPβ. And overexpressed PKM2 can partially restore MCE, although it did not restore terminal adipocyte differentiation, which was inhibited by siC/EBPβ. Thus, PKM2, potentially regulated by C/EBPβ, is involved in MCE during adipocyte differentiation. The dynamic proteome changes quantified here provide a promising basis for revealing molecular mechanism regulating adipogenesis.

Aberrant Overexpression of Pyruvate Kinase M2 Is Associated With Aggressive Tumor Features and theBRAFMutation in Papillary Thyroid Cancer

Many tumor cells predominantly generate energy through high rates of glycolysis. Pyruvate kinase M2 (PKM2) has been identified as being necessary for aerobic glycolysis. The aim of this study was to investigate the expression pattern of PKM2 in papillary thyroid cancer (PTC) and the possible role of PKM2 in PTC. The expression of PKM2 in human thyroid tissues was examined using immunocytochemistry. PKM2 expression in PTC correlated with clinicopathological features and the BRAF mutation. PTC cells were transfected with small interfering RNA against PKM2. PKM2 expression in cells was analyzed by Western blotting and real-time RT-PCR. Cell growth was evaluated both in vitro and in vivo. Lactate and ATP production and glucose consumption by cells were determined using commercial assay kits. PKM2 was aberrantly overexpressed in PTC. This overexpression was associated with poor clinicopathological features including advanced tumor stages and lymph node metastasis. More intensive immunostaining of PKM2 was detected in PTCs harboring the BRAF mutation. Specific small interfering RNA against PKM2 in PTC cell lines retarded cell growth both in vitro and in xenograft mouse models. PKM2 knockdown also reduced lactate and ATP production and glucose consumption by PTC cells. We conclude that overexpression of PKM2 provides a selective growth advantage for PTC cells through activation of glycolysis. Aberrant PKM2 overexpression may serve as a novel biomarker and a potential treatment target for PTC. The BRAF mutation may contribute to alterations in the expression pattern of glycolytic enzymes such as PKM2.

Insulin enhances metabolic capacities of cancer cells by dual regulation of glycolytic enzyme pyruvate kinase M2

BackgroundInsulin is tightly associated with cancer progression; however, mechanistic insights into such observations are poorly understood. Recent studies show that metabolic transformation is critical to cancer cell proliferation. Here, we attempt to understand the role of insulin in promotion of cancer metabolism. To this end, the role of insulin in regulating glycolytic enzyme pyruvate kinase M2 (PKM2) was examined.ResultsWe observed that insulin up-regulated PKM2 expression, through PI3K/mTOR mediated HIF1α induction, but significantly reduced PKM2 activity independent of this pathway. Drop in PKM2 activity was attributed to subunit dissociation leading to formation of low activity PKM2 oligomers, as assessed by density gradient centrifugation. However, tyrosine 105 phosphorylation of PKM2, known for inhibiting PKM2 activity, remained unaffected on insulin treatment. Interestingly, insulin-induced ROS was found responsible for PKM2 activity reduction. The observed changes in PKM2 status led to augmented cancer metabolism. Insulin-induced PKM2 up-regulation resulted in enhanced aerobic glycolysis as confirmed by PKM2 knockdown studies. Further, PKM2 activity reduction led to characteristic pooling of glycolytic intermediates and increased accumulation of NADPH; suggesting diversion of glucose flux towards macromolecular synthesis, necessary for cancer cell growth.ConclusionThe study identifies new PKM2-mediated effects of insulin on cancer metabolism, thus, advancing the understanding of insulin’s role in cancer.

PKM2 Moonlights as a Protein Kinase

Pyruvate kinase M2 phosphorylates the transcription factor STAT3.

Prolactin Inhibits Activity of Pyruvate Kinase M2 to Stimulate Cell Proliferation

Mitogenic and prosurvival effects underlie the tumorigenic roles of prolactin (PRL) in the pathogenesis of breast cancer. PRL signaling is mediated through its receptor (PRLr). A proteomics screen identified the pyruvate kinase M2 (PKM2), a glycolytic enzyme known to play an important role in tumorigenesis, as a protein that constitutively interacts with PRLr. Treatment of cells with PRL inhibited pyruvate kinase activity and increased the lactate content in human cells in a manner that was dependent on the abundance of PRLr, activation of Janus kinase 2, and tyrosine phosphorylation of the intracellular domain of PRLr. Knockdown of PKM2 attenuated PRL-stimulated cell proliferation. The extent of this proliferation was rescued by the knock-in of the wild-type PKM2 but not of its mutant insensitive to PRL-mediated inhibition. We discuss a hypothesis that the inhibition of PKM2 by PRL contributes to the PRL-stimulated cell proliferation.