Yap/Taz activity is associated with increased expression of phosphoglycerate dehydrogenase that supports myoblast proliferation

In skeletal muscle, the Hippo effector Yap promotes satellite cell, myoblast, and rhabdomyoblast proliferation but prevents myogenic differentiation into multinucleated muscle fibres. We previously noted that Yap drives expression of the first enzyme of the serine biosynthesis pathway, phosphoglycerate dehydrogenase (Phgdh). Here, we examined the regulation and function of Phgdh in satellite cells and myoblasts and found that Phgdh protein increased during satellite cell activation. Analysis of published data reveal that Phgdh mRNA in mouse tibialis anterior muscle was highly expressed at day 3 of regeneration after cardiotoxin injection, when markers of proliferation are also robustly expressed and in the first week of synergist-ablated muscle. Finally, siRNA-mediated knockdown of PHGDH significantly reduced myoblast numbers and the proliferation rate. Collectively, our data suggest that Phgdh is a proliferation-enhancing metabolic enzyme that is induced when quiescent satellite cells become activated.

Homoharringtonine as a PHGDH inhibitor: Unraveling metabolic dependencies and developing a potent therapeutic strategy for high-risk neuroblastoma

Neuroblastoma, a childhood cancer affecting the sympathetic nervous system, continues to challenge the development of potent treatments due to the limited availability of druggable targets for this aggressive illness. Recent investigations have uncovered that phosphoglycerate dehydrogenase (PHGDH), an essential enzyme for de novo serine synthesis, serves as a non-oncogene dependency in high-risk neuroblastoma. In this study, we show that homoharringtonine (HHT) acts as a PHGDH inhibitor, inducing intricate alterations in cellular metabolism, and thus providing an efficient treatment for neuroblastoma. We have experimentally verified the reliance of neuroblastoma on PHGDH and employed molecular docking, thermodynamic evaluations, and X-ray crystallography techniques to determine the bond interactions between HHT and PHGDH. Administering HHT to treat neuroblastoma resulted in effective cell elimination in vitro and tumor reduction in vivo. Metabolite and functional assessments additionally disclosed that HHT treatment suppressed de novo serine synthesis, initiating intricate metabolic reconfiguration and oxidative stress in neuroblastoma. Collectively, these discoveries highlight the potential of targeting PHGDH using HHT as a potent approach for managing high-risk neuroblastoma.

Identification of a novel PHGDH covalent inhibitor by chemical proteomics and phenotypic profiling

The first rate-limiting enzyme of the serine synthesis pathway (SSP), phosphoglycerate dehydrogenase (PHGDH), is hyperactive in multiple tumors, which leads to the activation of SSP and promotes tumorigenesis. However, only a few inhibitors of PHGDH have been discovered to date, especially the covalent inhibitors of PHGDH. Here, we identified withangulatin A (WA), a natural small molecule, as a novel covalent inhibitor of PHGDH. Affinity-based protein profiling identified that WA could directly bind to PHGDH and inactivate the enzyme activity of PHGDH. Biolayer interferometry and LC-MS/MS analysis further demonstrated the selective covalent binding of WA to the cysteine 295 residue (Cys295) of PHGDH. With the covalent modification of Cys295, WA blocked the substrate-binding domain (SBD) of PHGDH and exerted an allosteric effect to induce PHGDH inactivation. Further studies revealed that with the inhibition of PHGDH mediated by WA, the glutathione synthesis was decreased and intracellular levels of reactive oxygen species (ROS) were elevated, leading to the inhibition of tumor proliferation. This study indicates WA as a novel PHGDH covalent inhibitor, which identifies Cys295 as a novel allosteric regulatory site of PHGDH and holds great potential in developing anti-tumor agents for targeting PHGDH.

Phosphoglycerate dehydrogenase genes differentially affect Arabidopsis metabolism and development

Unlike animals, plants possess diverse L-serine (Ser) biosynthetic pathways. One of them, the Phosphorylated Pathway of Serine Biosynthesis (PPSB) has been recently described as essential for embryo, pollen and root development, and required for ammonium and sulfur assimilation. The first and rate limiting step of PPSB is the reaction catalyzed by the enzyme phosphoglycerate dehydrogenase (PGDH). In Arabidopsis, the PGDH family consists of three genes, PGDH1, PGDH2 and PGDH3. PGDH1 is characterized as being the essential gene of the family. However, the biological significance of PGDH2 and PGDH3 remains unknown. In this manuscript, we have functionally characterized PGDH2 and PGDH3. Phenotypic, metabolomic and gene expression analysis in PGDH single, double and triple mutants indicate that both PGDH2 and PGDH3 are functional, affecting plant metabolism and development. PGDH2 has a stronger effect on plant growth than PGDH3, having a partial redundant role with PGDH1. PGDH3, however, could have additional functions in photosynthetic cells unrelated to Ser biosynthesis.

A retrospective overview of PHGDH and its inhibitors for regulating cancer metabolism

Emerging evidence suggests that cancer metabolism is closely associated to the serine biosynthesis pathway (SSP), in which glycolytic intermediate 3-phosphoglycerate is converted to serine through a three-step enzymatic transformation. As the rate-limiting enzyme in the first step of SSP, phosphoglycerate dehydrogenase (PHGDH) is overexpressed in various diseases, especially in cancer. Genetic knockdown or silencing of PHGDH exhibits obvious anti-tumor response both in vitro and in vivo, demonstrating that PHGDH is a promising drug target for cancer therapy. So far, several types of PHGDH inhibitors have been identified as a significant and newly emerging option for anticancer treatment. Herein, this comprehensive review summarizes the recent achievements of PHGDH, especially its critical role in cancer and the development of PHGDH inhibitors in drug discovery.

Prognostic significance of phosphoglycerate dehydrogenase in breast cancer

PURPOSE

Breast cancer is the most common type of cancer affecting women worldwide. Phosphoglycerate dehydrogenase (PHGDH) is an oxidoreductase in the serine biosynthesis pathway. Although it has been reported to affect growth of various tumors, its role in breast cancer is largely unknown. This study aimed to analyze the expression of PHGDH in breast cancer tissue samples and to determine if PHGDH regulates breast cancer cell proliferation.

METHODS

Tissue microarrays consisting of 305 cases of breast invasive ductal carcinoma were used for immunohistochemical evaluation of PHGDH expression. The role of PHGDH in breast cancer was investigated in vitro by knocking down its expression and determining the effect on cell proliferation and cell cycling, and in ovo by using a chorioallantoic membrane (CAM) assay.

RESULTS

Immunohistochemical examination showed that PHGDH is mainly localized in the cytoplasm of breast cancer cells and significantly associated with higher cancer grade, larger tumor size, increased PCNA expression, and lymph node positivity. Analysis of the GOBO dataset of 737 patients demonstrated that increased PHGDH expression was associated with poorer overall survival. Knockdown of PHGDH expression in breast cancer cells in vitro resulted in a decrease in cell proliferation, reduction in cells entering the S phase of the cell cycle, and downregulation of various cell cycle regulatory genes. The volume of breast tumor in an in ovo CAM assay was found to be smaller when PHGDH was silenced.

CONCLUSION

The findings suggest that PHGDH has a regulatory role in breast cancer cell proliferation and may be a potential prognostic marker and therapeutic target in breast cancer.

PGDH family genes differentially affect Arabidopsis tolerance to salt stress

The first step in the Phosphorylated Pathway of serine (Ser) Biosynthesis (PPSB) is catalyzed by the enzyme Phosphoglycerate Dehydrogenase (PGDH), coded in Arabidopsis thaliana by three genes. Gene expression analysis indicated that PGDH1 and PGDH2 were induced, while PGDH3 was repressed, by salt-stress. Accordingly, PGDH3 overexpressing plants (Oex PGDH3) were more sensitive to salinity than wild type plants (WT), while plants overexpressing PGDH1 (Oex PGDH1) performed better than WT under salinity conditions. Oex PGDH1 lines displayed lower levels of the salt-stress markers proline and raffinose in roots than WT under salt-stress conditions. Besides, the ratio of oxidized glutathione (GSSG) without and with salt-stress was the highest in Oex PGDH1, and the lowest in Oex PGDH3 compared to WT. These results corroborated that PGDH3 activity could be detrimental, while PGDH1 activity could be beneficial for plant salt tolerance. Under salt-stress conditions, PGDH1 overexpression increased Ser content only in roots, while PGDH3 overexpression increased the amino acid level in both aerial parts and roots, compared to the WT. Our results indicate that the response of PGDH family genes to salt-stress depends on the specific gene studied and that increases in Ser content are not always correlated with enhanced plant salt tolerance.

Knockdown of PHGDH potentiates 5-FU cytotoxicity in gastric cancer cells via the Bcl-2/Bax/caspase-3 signaling pathway

Gastric cancer (GC) is one of the most common malignancies in the world. Fluorouracil (5-FU) is widely used in the treatment of cancers, but resistance to 5-FU results in the failure of chemotherapy. Phosphoglycerate dehydrogenase (PHGDH) has been reported to play a vital role in the development of 5-FU resistance in cancer cells. However, the exact role of PHGDH and the underlying mechanisms for 5-FU resistance in GC cells remain elusive. In this study, PHGDH expression was much higher in the GC tissues of 5-FU-resistant patients than that in the GC tissues of 5-FU-sensitive patients. Moreover, the expression of PHGDH was obviously increased in BGC823/5-FU cells compared with that in BGC823 cells. 5-FU treatment significantly reduced the viability of BGC823/5-FU cells, in a dose- and time-dependent manner. Furthermore, 5-FU treatment inhibited the proliferation of BGC823/5-FU cells, as evidenced by decreased cell viability and reduced colony-forming ability. The knockdown of PHGDH made possible the inhibitory effect of 5-FU on the proliferation of BGC823/5-FU cells. Furthermore, 5-FU treatment promoted apoptosis of BGC823/5-FU cells, as indicated by increased numbers of TUNEL-positive cells and increased rates of apoptosis. Notably, the promoting effect of 5-FU on the apoptosis of BGC823/5-FU cells was markedly enhanced by PHGDH knockdown. Additionally, 5-FU treatment downregulated Bcl-2 expression and upregulated the expression of Bax and caspase-3, and this effect was remarkably enhanced by PHGDH knockdown. In conclusion, knockdown of PHGDH potentiates 5-FU cytotoxicity in GC cells via the Bcl-2/Bax/caspase-3 signaling pathway.

LncRNA PlncRNA-1 overexpression inhibits the growth of breast cancer by upregulating TGF-β1 and downregulating PHGDH

OBJECTIVE

To investigate the role of lncRNA PlncRNA-1 in the pathogenesis of breast cancer.

METHODS

A total of 78 patients with breast cancer as well as 48 healthy females were included in this study. Expression in tumor tissues and adjacent healthy tissues of breast cancer patients, as well as in breast tissues and serum of both patients and healthy control was detected by qRT-PCR. Cell proliferation was detected by CCK-8 assay, and cell apoptosis was tested by MTT assay. PlncRNA-1 overexpression cell lines were constructed and the effects on TGF-β1 as well as phosphoglycerate dehydrogenase (PHGDH) were explored by western blot.

RESULTS

Expression levels of PlncRNA-1 were significantly lower in tumor tissues than those in adjacent healthy tissues. Significantly lower expression levels of PlncRNA-1 were also found in breast cancer patients than those in healthy controls in both breast tissue and serum. Upregulation of PlncRNA-1 promoted the expression of TGF-β1, but inhibited the expression of PHGDH. LncRNA PlncRNA-1 overexpression reduced the proliferation rate, but increased the apoptosis rate of breast cancer cells, while treatment with TGF-β inhibitor reduced those effects of PlncRNA-1 overexpression.

CONCLUSION

LncRNA PlncRNA-1 overexpression inhibits the growth of breast cancer by upregulating TGF-β1 and downregulating PHGDH.

Disruption of De Novo Serine Synthesis in Müller Cells Induced Mitochondrial Dysfunction and Aggravated Oxidative Damage

De novo serine synthesis plays important roles in normal mitochondrial function and cellular anti-oxidative capacity. It is reported to be mainly activated in glial cells of the central nervous system, but its role in retinal Müller glia remains unclear. In this study, we inhibited de novo serine synthesis using CBR-5884, a specific inhibitor of phosphoglycerate dehydrogenase (PHGDH, a rate limiting enzyme in de novo serine metabolism) in MIO-M1 cells (immortalized human Müller cells) and huPMCs (human primary Müller cells) under mild oxidative stress. Alamar blue and LDH (lactate dehydrogenase) assays showed significantly reduced metabolic activities and increased cellular damage of Müller cells, when exposed to CBR-5884 accompanied by mild oxidative stress; however, CBR-5884 alone had little effect. The increased cellular damage was partially reversed by supplementation with exogenous serine/glycine. HSP72 (an oxidative stress marker) and reactive oxygen species (ROS) levels were significantly increased; glutathione and NADPH/NADP⁺ levels were pronouncedly reduced under PHGDH inhibition accompanied by oxidative stress. JC-1 staining and Seahorse respiration experiments showed that inhibition of de novo serine synthesis in Müller cells can also increase mitochondrial stress and decrease mitochondrial ATP production. qPCR and Western blot demonstrated an increased expression of HSP60 (a key mitochondrial stress-related gene), and this was further validated in human retinal explants. Our study suggests that de novo serine synthesis is important for Müller cell survival, particularly when they are exposed to mild oxidative stress, possibly by maintaining mitochondrial function and generating glutathione and NADPH to counteract ROS.

An epitope tag alters phosphoglycerate dehydrogenase structure and impairs ability to support cell proliferation

Background

The gene encoding the serine biosynthesis pathway enzyme PHGDH is located in a region of focal genomic copy number gain in human cancers. Cells with PHGDH amplification are dependent on enzyme expression for proliferation. However, dependence on increased PHGDH expression extends beyond production of serine alone, and further studies of PHGDH function are necessary to elucidate its role in cancer cells. These studies will require a physiologically relevant form of the enzyme for experiments using engineered cell lines and recombinant protein.

Results

The addition of an N-terminal epitope tag to PHGDH abolished the ability to support proliferation of PHGDH-amplified cells despite retention of some activity to convert 3-PG to PHP. Introducing an R236E mutation into PHGDH eliminates enzyme activity, and this catalytically inactive enzyme cannot support proliferation of PHGDH-dependent cells, arguing that canonical enzyme activity is required. Tagged and untagged PHGDH exhibit the same intracellular localization and ability to produce D-2-hydroxyglutarate (D-2HG), an error product of PHGDH, arguing that neither mislocalization nor loss of D-2HG production explains the inability of epitope-tagged PHGDH to support proliferation. To enable studies of PHGDH function, we report a method to purify recombinant PHGDH and found that untagged enzyme activity was greater than N-terminally tagged enzyme. Analysis of tagged and untagged PHGDH using size exclusion chromatography and electron microscopy found that an N-terminal epitope tag alters enzyme structure.

Conclusions

Purification of untagged recombinant PHGDH eliminates the need to use an epitope tag for enzyme studies. Furthermore, while tagged PHGDH retains some ability to convert 3PG to PHP, the structural alterations caused by including an epitope tag disrupts the ability of PHGDH to sustain cancer cell proliferation.

Electronic supplementary material

The online version of this article (doi:10.1186/s40170-015-0131-7) contains supplementary material, which is available to authorized users.