Mechanosensitive turnover of phosphoribosyl pyrophosphate synthetases regulates nucleotide metabolism

p63 affects distinct metabolic pathways during keratinocyte senescence, evaluated by metabolomic profile and gene expression analysis

Unraveling the molecular nature of skin aging and keratinocyte senescence represents a challenging research project in epithelial biology. In this regard, depletion of p63, a p53 family transcription factor prominently expressed in human and mouse epidermis, accelerates both aging and the onset of senescence markers in vivo animal models as well as in ex vivo keratinocytes. Nonetheless, the biochemical link between p63 action and senescence phenotype remains largely unexplored. In the present study, through ultrahigh performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS) and gas chromatography/mass spectrometry (GC/MS) metabolomic analysis, we uncover interesting pathways linking replicative senescence to metabolic alterations during p63 silencing in human keratinocytes. Integration of our metabolomic profiling data with targeted transcriptomic investigation empowered us to demonstrate that absence of p63 and senescence share similar modulation profiles of oxidative stress markers, pentose phosphate pathway metabolites and lyso-glycerophospholipids, the latter due to enhanced phospholipases gene expression profile often under p63 direct/indirect gene control. Additional biochemical features identified in deranged keratinocytes include a relevant increase in lipids production, glucose and pyruvate levels as confirmed by upregulation of gene expression of key lipid synthesis and glycolytic enzymes, which, together with improved vitamins uptake, characterize senescence phenotype. Silencing of p63 in keratinocytes instead, translates into a blunted flux of metabolites through both glycolysis and the Krebs cycle, likely due to a p63-dependent reduction of hexokinase 2 and citrate synthase gene expression. Our findings highlight the potential role of p63 in counteracting keratinocyte senescence also through fine regulation of metabolite levels and relevant biochemical pathways. We believe that our research might contribute significantly to the discovery of new implications of p63 in keratinocyte senescence and related diseases.

IL-6/JAK2-dependent G6PD phosphorylation promotes nucleotide synthesis and supports tumor growth

OBJECTIVE

Tumor cells hijack inflammatory mechanisms to promote their own growth. IL-6 is one of the major cytokines, and is frequently upregulated in tumors. The pentose phosphate pathway (PPP) generates the indispensable building blocks to produce various nucleotides. Here we aimed to determine whether and how PPP is timely tuned in response to IL-6 to support tumor growth.

METHODS

Protein expression was examined by immunoblot. Protein interaction was examined by immunoprecipitation. Tumor cell proliferation in in vitro culture was examined by BrdU assay and colony formation assay. Tumor cell proliferation in mouse xenograft model was examined by Ki-67 staining.

RESULTS

Here we show that the metabolic flux of PPP and enzymatic activity of glucose-6-phosphate dehydrogenase (G6PD) is rapidly induced under IL-6 treatment, without obvious changes in G6PD expression level. Mechanistically, Janus kinase 2 (JAK2) phosphorylates G6PD Y437 under IL-6 treatment, which accentuates G6PD enzymatic activity by promoting G6PD binding with its substrate G6P. Further, JAK2-dependent G6PD Y437 phosphorylation is required for IL-6-induced nucleotide biosynthesis and tumor cell proliferation, and is associated with the progression of oral squamous cell carcinoma.

CONCLUSIONS

Our findings report a new mechanism implicated in the crosstalk between tumor cells and inflammatory microenvironment, by which JAK2-dependent activation of G6PD governs nucleotide synthesis to support tumor cell proliferation, thereby highlighting its value as a potential anti-tumor target.

Rapid phosphorylation of glucose-6-phosphate dehydrogenase by casein kinase 2 sustains redox homeostasis under ionizing radiation

Exposure to ionizing radiation leads to oxidative damages in living cells. NADPH provides the indispensable reducing power to regenerate the reduced glutathione to maintain cellular redox equilibria. In mammalian cells, pentose phosphate pathway (PPP) is the major route to produce NADPH by using glycolytic intermediates, and the rate-limiting step of PPP is controlled by glucose-6-phosphate dehydrogenase (G6PD). Nevertheless, whether G6PD is timely co-opted under ionizing radiation to cope with oxidative stress remains elusive. Here we show that cellular G6PD activity is induced 30 min after ionizing radiation, while its protein expression is mostly unchanged. Mechanistically, casein kinase 2 (CK2) phosphorylates G6PD T145 under ionizing radiation, which consolidates the enzymatic activity of G6PD by facilitating G6PD binding with its substrate NADP+. Further, CK2-dependent G6PD T145 phosphorylation promotes NADPH production, decreases ROS level and supports cell proliferation under ionizing radiation. Our findings report a new anti-oxidative signaling route under ionizing radiation, by which CK2-mediated rapid activation of G6PD orchestrates NADPH synthesis to maintain redox homeostasis, thereby highlighting its potential value in the early treatment of ionizing radiation-induced injuries.

Extracellular-matrix mechanics regulate cellular metabolism: A ninja warrior behind mechano-chemo signaling crosstalk

Mechanical forces are the indispensable constituent of environmental cues, such as gravity, barometric pressure, vibration, and contact with bodies, which are involved in pattern and organogenesis, providing mechanical input to tissues and determining the ultimate fate of cells. Extracellular matrix (ECM) stiffness, the slow elastic force, carries the external physical force load onto the cell or outputs the internal force exerted by the cell and its neighbors into the environment. Accumulating evidence illustrates the pivotal role of ECM stiffness in the regulation of organogenesis, maintenance of tissue homeostasis, and the development of multiple diseases, which is largely fulfilled through its systematical impact on cellular metabolism. This review summarizes the establishment and regulation of ECM stiffness, the mechanisms underlying how ECM stiffness is sensed by cells and signals to modulate diverse cell metabolic pathways, and the physiological and pathological significance of the ECM stiffness-cell metabolism axis.

Hippo pathway monomerizes STAT3 to regulate prostate cancer growth

Prostate cancer ranks among the most commonly diagnosed malignancies for men, and has become a non-negligible threat for public health. Interplay between inflammatory factors and cancer cells renders inflammatory tissue environment as a predisposing condition for cancer development. The Hippo pathway is a conserved signaling pathway across multiple species during evolution that regulates tissue homeostasis and organ development. Nevertheless, whether Hippo pathway regulates cancer-related inflammatory factors remain elusive. Here we show that high cell density-mediated activation of Hippo pathway blunts STAT3 activity in prostate cancer cells. Hippo pathway component MST2 kinase phosphorylates STAT3 at T622, which is located in the SH2 domain of STAT3. This phosphorylation blocks SH2 domain in one STAT3 molecule to bind with the phosphorylated Y705 site in another STAT3 molecule, which further counteracts IL6-induced STAT3 dimerization and activation. Expression of a non-phosphoryable STAT3 T622A mutant enhances STAT3 activity and IL6 expression at high cell density, and promotes tumor growth in mice xenograft model. Our findings demonstrate that STAT3 is a novel phosphorylation substrate for MST2, and thereby highlight a regulatory cascade underlying the crosstalk between inflammation and Hippo pathway in prostate cancer cells.

Targeting extracellular matrix stiffness and mechanotransducers to improve cancer therapy

Cancer microenvironment is critical for tumorigenesis and cancer progression. The extracellular matrix (ECM) interacts with tumor and stromal cells to promote cancer cells proliferation, migration, invasion, angiogenesis and immune evasion. Both ECM itself and ECM stiffening-induced mechanical stimuli may activate cell membrane receptors and mechanosensors such as integrin, Piezo1 and TRPV4, thereby modulating the malignant phenotype of tumor and stromal cells. A better understanding of how ECM stiffness regulates tumor progression will contribute to the development of new therapeutics. The rapidly expanding evidence in this research area suggests that the regulators and effectors of ECM stiffness represent potential therapeutic targets for cancer. This review summarizes recent work on the regulation of ECM stiffness in cancer, the effects of ECM stiffness on tumor progression, cancer immunity and drug resistance. We also discuss the potential targets that may be druggable to intervene ECM stiffness and tumor progression. Based on these advances, future efforts can be made to develop more effective and safe drugs to interrupt ECM stiffness-induced oncogenic signaling, cancer progression and drug resistance.