Biology subjects

Swietach, P.

Publications and source records attributed to Swietach, P..

5 recordsLinked to original sources

bioRxiv2024

Contact-based thymidylate transfer promotes collective tumor growth

Sustained cell proliferation is a fundamental hallmark of cancer, yet its mechanism remains elusive, particularly in context of heterogenous tumor organization, intercellular interactions, and metabolite exchanges. In this study, we uncover a mechanism of tumor growth via collective proliferation, where cells connected by gap junctions enable equilibration of thymidylate (dTMP) to allow the proliferation of cells lacking canonical de novo dTMP biosynthesis and salvage driven by thymidylate synthase (TYMS) and thymidine kinase 1 (TK1) enzymes, respectively. Collective proliferation is driven by dTMP-proficient cancer cells alongside cells of varied origins, such as macrophages and endothelial cells. The mechanism is also observed in clinical samples and is validated in a genetic mouse model of lung cancer harboring dual Tyms/Tk1 tumor-specific knockout, in which tumors grow despite lacking enzymatic dTMP synthesis and tumor progression is opposed by gap junction inhibition. Data further hint that this mechanism is critical driver of tumor pathophysiology, influencing key processes such as senescence, genomic instability and drug resistance. These findings revise the current dogma of ubiquitous nucleotide biosynthesis in each proliferating cancer cell in a tumor and suggest that a programmed dTMP distribution maintains collective tumor growth. This mechanism could be exploited in cancer therapy.

cancer biology↗

bioRxiv2024

Lysosomal signalling pathways influence heart rhythm, and regulate atrial function

In the heart, endogenous nicotinic acid adenine dinucleotide phosphate (NAADP) triggers lysosomal calcium (Ca2+) release to augment sarcoplasmic reticulum (SR) Ca2+ sequestration, producing larger Ca2+ transients. However, the role of lysosomal Ca2+ signals in pacemaker activity, a distinct Ca2+-operated function of the sinoatrial node (SAN), or in the atrial myocardium has not been investigated. Pharmacological or genetic ablation of the NAADP pathway inhibits the spontaneous beating rate response to beta-adrenergic stimulation in intact SAN. We found intracellular signaling microdomains between lysosomes and neighboring SR or mitochondria in mouse, and goat tissue. The spatial relationship between lysosomes and other Ca2+-handling organelles are altered in goat atrial fibrillation. Furthermore, we demonstrate atrial myocytes produce cAMP in response to lysosomal signaling, adding a novel trigger for cyclic nucleotide signaling. Our findings support the hypothesis that lysosomal Ca2+ signaling contributes to regulation of cardiomyocyte cAMP levels and pacemaker activity.

physiology↗

bioRxiv2022

Solute exchange through gap junctions lessens the adverse effects of inactivating mutations in metabolite-handling genes

Experimental inactivation of certain genes involved in metabolism attenuates cancer cell growth in vitro. However, loss-of-function mutations in metabolic pathways are not negatively selected in human cancers, indicating that these genes are not essential in vivo. We hypothesize that spontaneous mutations affecting metabolic pathways do not necessarily result in a functional defect because affected cells may be rescued by exchanging metabolites with neighboring wild-type cells via gap junctions. Using fluorescent substances to probe inter-cellular diffusion, we show that colorectal cancer (CRC) cells are coupled by gap junctions assembled from connexins, particularly the constitutively expressed Cx26. In co-cultures of wild-type cells with cells that had inactivated components of pH regulation (SLC9A1), glycolysis (ALDOA), or mitochondrial metabolism (NDUFS1), we show that diffusive coupling was able to rescue the functional defect associated with the inactivation of metabolite-handling genes. Function rescue was dependent on Cx26 channels and reduced phenotypic heterogeneity among cells. Since the phenotypic landscape did not map onto genotype, an individual cell should not be considered as the unit under selection, at least in the case of metabolite-handling processes. Our findings can explain why certain loss-of-function mutations in genes, previously ascribed as being essential, do not influence the growth of human cancers.

cancer biology↗

bioRxiv2021

Proton export drives the Warburg Effect

Aggressive cancers commonly ferment glucose to lactic acid at high rates, even in the presence of oxygen. This is known as aerobic glycolysis, or the "Warburg Effect". It is widely assumed that this is a consequence of the upregulation of glycolytic enzymes. Oncogenic drivers can increase the expression of most proteins in the glycolytic pathway, including the terminal step of exporting H+ equivalents from the cytoplasm. Proton exporters maintain an alkaline cytoplasmic pH, which can enhance all glycolytic enzyme activities, even in the absence of oncogene-related expression changes. Based on this observation, we hypothesized that increased uptake and fermentative metabolism of glucose could be driven by the expulsion of H+ equivalents from the cell. To test this hypothesis, we stably transfected lowly-glycolytic MCF-7, U2-OS, and glycolytic HEK293 cells to express proton exporting systems: either PMA1 (yeast H+-ATPase) or CAIX (carbonic anhydrase 9). The expression of either exporter in vitro enhanced aerobic glycolysis as measured by glucose consumption, lactate production, and extracellular acidification rate. This resulted in an increased intracellular pH, and metabolomic analyses indicated that this was associated with an increased flux of all glycolytic enzymes upstream of pyruvate kinase. These cells also demonstrated increased migratory and invasive phenotypes in vitro, and these were recapitulated in vivo by more aggressive behavior, whereby the acid-producing cells formed higher grade tumors with higher rates of metastases. Neutralizing tumor acidity with oral buffers reduced the metastatic burden. Therefore, cancer cells with increased H+ export increase intracellular alkalization, even without oncogenic driver mutations, and this is sufficient to alter cancer metabolism towards a Warburg phenotype.

cancer biology↗

bioRxiv2019

Lymph Nodes Inhibit T-cell Effector Functions Locally by Establishing Acidic Niches

Lymph nodes are an essential component of the adaptive immune response where antigen-presenting cells are closely housed with their cognate effector cells. Protection of lymph node resident cells from activated immune cells in such close quarters would need to be robust and reversible. Effector functions of T-cells are profoundly and reversibly inhibited by an acidic microenvironment. The underlying mechanisms of this inhibition are unknown, but may relate to glycolysis, which is obligatory for expression of effector functions. Here, we demonstrate that acidification rapidly and potently inhibits monocarboxylate transporter-dependent lactic acid efflux, which dually inhibits glycolysis by end-product accumulation and by reducing cytoplasmic pH. Based on the robustness of these responses, we propose that acid-evoked T-cell inhibition is physiologically important, and that lymph nodes are a natural site for such modulation. Using multiple imaging techniques, we show that paracortical T-zones of lymph nodes are highly acidic. We further show that T-cells can be activated by dendritic cells at low pH, and their effector functions are restored rapidly upon increasing pH. Thus, we describe a novel physiological mechanism whereby activated T-cells are kept in stasis by acidosis whilst resident in lymph nodes.

physiology↗