Functional consequences of C-terminal mutations in RUNX2.

Cleidocranial dysplasia (CCD) is a genetic disorder caused by mutations in the RUNX2 gene, affecting bone and teeth development. Previous studies focused on mutations in the RUNX2 RHD domain, with limited investigation of mutations in the C-terminal domain. This study aimed to investigate the functional consequences of C-terminal mutations in RUNX2. Eight mutations were analyzed, and their effects on transactivation activity, protein expression, subcellular localization, and osteogenic potential were studied. Truncating mutations in the PST region and a missense mutation in the NMTS region resulted in increased transactivation activity, while missense mutations in the PST showed activity comparable to the control. Truncating mutations produced truncated proteins, while missense mutations produced normal-sized proteins. Mutant proteins were mislocalized, with six mutant proteins detected in both the nucleus and cytoplasm. CCD patient bone cells exhibited mislocalization of RUNX2, similar to the generated mutant. Mislocalization of RUNX2 and reduced expression of downstream genes were observed in MSCs from a CCD patient with the p.Ser247Valfs*3 mutation, leading to compromised osteogenic potential. This study provides insight into the functional consequences of C-terminal mutations in RUNX2, including reduced expression, mislocalization, and aberrant transactivation of downstream genes, contributing to the compromised osteogenic potential observed in CCD.

The role of the phosphate groups of trinitrophenyl adenosine 5'-triphosphate (TNP-ATP) in allosteric activation of pyruvate carboxylase and the inhibition of acetyl CoA-dependent activation.

A previous study showed that 2'-3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP) was a weak allosteric activator of Rhizobium etli pyruvate carboxylase (RePC) in the absence of acetyl-CoA. On the other hand, TNP-ATP inhibited the allosteric activation of RePC by acetyl-CoA. Here, we aimed to study the role of triphosphate group of TNP-ATP on its allosteric activation of the enzyme and inhibition of acetyl-CoA-dependent activation of RePC using TNP-ATP and its derivatives, including TNP-ADP, TNP-AMP and TNP-adenosine. The pyruvate carboxylation activity was assayed to determine the effect of reducing the number of phosphate groups in TNP-ATP derivatives on allosteric activation and inhibition of acetyl-CoA activation of RePC and chicken liver pyruvate carboxylase (CLPC). Reducing the number of phosphate groups in TNP-ATP derivatives decreased the activation efficacy for both RePC and CLPC compared to TNP-ATP. The apparent binding affinity and inhibition of activation of the enzymes by acetyl-CoA were also diminished when the number of phosphate groups in the TNP-ATP derivatives was reduced. Whilst TNP-AMP activated RePC, it did not activate CLPC, but it did inhibit acetyl-CoA activation of both RePC and CLPC. Similarly, TNP-adenosine did not activate RePC; however, it did inhibit acetyl-CoA activation using a different mechanism compared to phosphorylated TNP-derivatives. These findings indicate that mechanisms of PC activation and inhibition of acetyl-CoA activation by TNP-ATP and its derivatives are different. This study provides the basis for possible drug development for treatment of metabolic diseases and cancers with aberrant expression of PC.

Impaired G2/M cell cycle arrest induces apoptosis in pyruvate carboxylase knockdown MDA-MB-231 cells.

BACKGROUND: Previous studies showed that suppression of pyruvate carboxylase (PC) expression in highly invasive breast cancer cell line, MDA-MB-231 inhibits cell growth as a consequence of the impaired cellular biosynthesis. However, the precise cellular mechanism underlying this growth restriction is unknown. METHODS: We generated the PC knockdown (PCKD) MDA-MB-231 cells and assessed their phenotypic changes by fluorescence microscopy, proliferation, apoptotic, cell cycle assays and proteomics. RESULTS: PC knockdown MDA-MB-231 cells had a low percentage of cell viability in association with accumulation of abnormal cells with large or multi-nuclei. Flow cytometric analysis of annexin V-7-AAD positive cells showed that depletion of PC expression triggers apoptosis with the highest rate at day 4. The increased rate of apoptosis is consistent with increased cleavage of procaspase 3 and poly (ADP-Ribose) polymerase. Cell cycle analysis showed that the apoptotic cell death was associated with G2/M arrest, in parallel with marked reduction of cyclin B levels. Proteomic analysis of PCKD cells identified 9 proteins whose expression changes were correlated with the degree of apoptosis and G2/M cell cycle arrest in the PCKD cells. STITCH analysis indicated 3 of 9 candidate proteins, CCT3, CABIN1 and HECTD3, that form interactions with apoptotic and cell cycle signaling networks linking to PC via MgATP. CONCLUSIONS: Suppression of PC in MDA-MB-231 cells induces G2/M arrest, leading to apoptosis. Proteomic analysis supports the potential involvement of PC expression in the aberrant cell cycle and apoptosis, and identifies candidate proteins responsible for the PC-mediated cell cycle arrest and apoptosis in breast cancer cells. GENERAL SIGNIFICANCE: Our results highlight the possibility of the use of PC as an anti-cancer drug target.

Generation of Human Pyruvate Carboxylase Knockout Cell Lines Using Retrovirus Expressing Short Hairpin RNA and CRISPR-Cas9 as Models to Study Its Metabolic Role in Cancer Research.

We report two protocols to generate human pyruvate carboxylase knockdown and knockout cell lines using short hairpin RNA (shRNA) and CRISPR-Cas9 technologies. The first protocol involved cloning of a shRNA cassette targeted to human pyruvate carboxylase (PC) under the control of a U6 promoter in a retrovirus-based vector. The stable knockdown cells were achieved following infection of retroviruses expressing shRNA in target cells followed by selecting these in medium containing puromycin. The second protocol describes a CRISPR Cas9-knockout cell constructed by cloning of single guide RNA (gRNA) targeted to the human pyruvate carboxylase gene placed adjacent to Cas 9 in the pSpCas9(BB)-2A-GFP vector. The knockout cells can be selected by sorting the cells expressing GFP. We also describe protocols for detecting the level of PC mRNA and protein in the knockdown or knockout cells using qPCR and Western blot analyses, respectively. The above protocols allow investigators to create PC deficient cell lines as a tool to study role of this enzyme in cancer research.

Mass spectrometry analysis shows the biosynthetic pathways supported by pyruvate carboxylase in highly invasive breast cancer cells.

We recently showed that the anaplerotic enzyme pyruvate carboxylase (PC) is up-regulated in human breast cancer tissue and its expression is correlated with the late stages of breast cancer and tumor size [Phannasil et al., PloS One 10, e0129848, 2015]. In the current study we showed that PC enzyme activity is much higher in the highly invasive breast cancer cell line MDA-MB-231 than in less invasive breast cancer cell lines. We generated multiple stable PC knockdown cell lines from the MDA-MB-231 cell line and used mass spectrometry with 13C6-glucose and 13C5-glutamine to discern the pathways that use PC in support of cell growth. Cells with severe PC knockdown showed a marked reduction in viability and proliferation rates suggesting the perturbation of pathways that are involved in cancer invasiveness. Strong PC suppression lowered glucose incorporation into downstream metabolites of oxaloacetate, the product of the PC reaction, including malate, citrate and aspartate. Levels of pyruvate, lactate, the redox partner of pyruvate, and acetyl-CoA were also lower suggesting the impairment of mitochondrial pyruvate cycles. Serine, glycine and 5-carbon sugar levels and flux of glucose into fatty acids were decreased. ATP, ADP and NAD(H) levels were unchanged indicating that PC suppression did not significantly affect mitochondrial energy production. The data indicate that the major metabolic roles of PC in invasive breast cancer are primarily anaplerosis, pyruvate cycling and mitochondrial biosynthesis of precursors of cellular components required for breast cancer cell growth and replication.

MicroRNAs and oncogenic transcriptional regulatory networks controlling metabolic reprogramming in cancers.

Altered cellular metabolism is a fundamental adaptation of cancer during rapid proliferation as a result of growth factor overstimulation. We review different pathways involving metabolic alterations in cancers including aerobic glycolysis, pentose phosphate pathway, de novo fatty acid synthesis, and serine and glycine metabolism. Although oncoproteins, c-MYC, HIF1α and p53 are the major drivers of this metabolic reprogramming, post-transcriptional regulation by microRNAs (miR) also plays an important role in finely adjusting the requirement of the key metabolic enzymes underlying this metabolic reprogramming. We also combine the literature data on the miRNAs that potentially regulate 40 metabolic enzymes responsible for metabolic reprogramming in cancers, with additional miRs from computational prediction. Our analyses show that: (1) a metabolic enzyme is frequently regulated by multiple miRs, (2) confidence scores from prediction algorithms might be useful to help narrow down functional miR-mRNA interaction, which might be worth further experimental validation. By combining known and predicted interactions of oncogenic transcription factors (TFs) (c-MYC, HIF1α and p53), sterol regulatory element binding protein 1 (SREBP1), 40 metabolic enzymes, and regulatory miRs we have established one of the first reference maps for miRs and oncogenic TFs that regulate metabolic reprogramming in cancers. The combined network shows that glycolytic enzymes are linked to miRs via p53, c-MYC, HIF1α, whereas the genes in serine, glycine and one carbon metabolism are regulated via the c-MYC, as well as other regulatory organization that cannot be observed by investigating individual miRs, TFs, and target genes.

Deletion of Mitochondrial Porin Alleviates Stress Sensitivity in the Yeast Model of Shwachman-Diamond Syndrome.

Shwachman-Diamond syndrome (SDS) is a multi-system disorder characterized by bone marrow failure, pancreatic insufficiency, skeletal abnormalities, and increased risk of leukemic transformation. Most patients with SDS contain mutations in the Shwachman-Bodian-Diamond syndrome gene (SBDS), encoding a highly conserved protein that has been implicated in ribosome biogenesis. Emerging evidence also suggests a distinct role of SBDS beyond protein translation. Using the yeast model of SDS, we examined the underlying mechanisms that cause cells lacking Sdo1p, the yeast SBDS ortholog, to exhibit reduced tolerance to various stress conditions. Our analysis indicates that the environmental stress response (ESR), heat shock response (HSR), and endoplasmic reticulum unfolded protein response (UPR) of sdo1Δ cells are functional and that defects in these pathways do not produce the phenotypes observed in sdo1Δ yeast. Depletion of mitochondrial DNA (mtDNA) was observed in sdo1Δ cells, and this is a probable cause of the mitochondrial insufficiency in SDS. Prior disruption of POR1, encoding the mitochondrial voltage dependent anion channel (VDAC), abrogated the effects of SDO1 deletion and substantially restored resistance to environmental stressors and protected against damage to mtDNA. Conversely, wild-type cells over-expressing POR1 exhibited growth impairment and increased stress sensitivity similar to that seen in sdo1Δ cells. Overall, our results suggest that specific VDAC inhibitors may have therapeutic benefits for SDS patients.