S1P lyase regulates DNA damage responses through a novel sphingolipid feedback mechanism

The injurious consequences of ionizing radiation (IR) to normal human cells and the acquired radioresistance of cancer cells represent limitations to cancer radiotherapy. IR induces DNA damage response pathways that orchestrate cell cycle arrest, DNA repair or apoptosis such that irradiated cells are either repaired or eliminated. Concomitantly and independent of DNA damage, IR activates acid sphingomyelinase (ASMase), which generates ceramide, thereby promoting radiation-induced apoptosis. However, ceramide can also be metabolized to sphingosine-1-phosphate (S1P), which acts paradoxically as a radioprotectant. Thus, sphingolipid metabolism represents a radiosensitivity pivot point, a notion supported by genetic evidence in IR-resistant cancer cells. S1P lyase (SPL) catalyzes the irreversible degradation of S1P in the final step of sphingolipid metabolism. We show that SPL modulates the kinetics of DNA repair, speed of recovery from G2 cell cycle arrest and the extent of apoptosis after IR. SPL acts through a novel feedback mechanism that amplifies stress-induced ceramide accumulation, and downregulation/inhibition of either SPL or ASMase prevents premature cell cycle progression and mitotic death. Further, oral administration of an SPL inhibitor to mice prolonged their survival after exposure to a lethal dose of total body IR. Our findings reveal SPL to be a regulator of ASMase, the G2 checkpoint and DNA repair and a novel target for radioprotection

A Prokaryotic S1P Lyase Degrades Extracellular S1P In Vitro and In Vivo: Implication for Treating Hyperproliferative Disorders

Sphingosine-1-phosphate (S1P) regulates a broad spectrum of fundamental cellular processes like proliferation, death, migration and cytokine production. Therefore, elevated levels of S1P may be causal to various pathologic conditions including cancer, fibrosis, inflammation, autoimmune diseases and aberrant angiogenesis. Here we report that S1P lyase from the prokaryote Symbiobacterium thermophilum (StSPL) degrades extracellular S1P in vitro and in blood. Moreover, we investigated its effect on cellular responses typical of fibrosis, cancer and aberrant angiogenesis using renal mesangial cells, endothelial cells, breast (MCF-7) and colon (HCT 116) carcinoma cells as disease models. In all cell types, wild-type StSPL, but not an inactive mutant, disrupted MAPK phosphorylation stimulated by exogenous S1P. Functionally, disruption of S1P receptor signaling by S1P depletion inhibited proliferation and expression of connective tissue growth factor in mesangial cells, proliferation, migration and VEGF expression in carcinoma cells, and proliferation and migration of endothelial cells. Upon intravenous injection of StSPL in mice, plasma S1P levels rapidly declined by 70% within 1 h and then recovered to normal 6 h after injection. Using the chicken chorioallantoic membrane model we further demonstrate that also under in vivo conditions StSPL, but not the inactive mutant, inhibited tumor cell-induced angiogenesis as an S1P-dependent process. Our data demonstrate that recombinant StSPL is active under extracellular conditions and holds promise as a new enzyme therapeutic for diseases associated with increased levels of S1P and S1P receptor signaling

True Religion and Hume's Practical Atheism

The argument and discussion in this paper begins from the premise that Hume was an atheist who denied the religious or theist hypothesis. However, even if it is agreed that that Hume was an atheist this does not tell us where he stood on the question concerning the value of religion. Some atheists, such as Spinoza, have argued that society needs to maintain and preserve a form of “true religion”, which is required for the support of our ethical life. Others, such as D’Holbach have argued that religion is not only false it is pernicious and it should be eradicated. This paper argues that Hume rejected both theseproposals, on the ground that they rest, in different ways, on excessively optimistic assumptions. The sensible, practical form of atheism that Hume defends has a more modest and realistic aim, which is simply to restrict and limit the most pernicious forms of religion. Understood this way, Hume’s practical atheism is very different from the forms of “old” atheism associated with Spinoza and D’Holbach, as well as from the “new atheism” of thinkers such as Dawkins and Dennett. Reprinted in Paul Russell, "Recasting Hume and Early Modern Philosophy: Selected Essays" (New York: Oxford University Press, 2021): 340-383

Primary HPV and Molecular Cervical Cancer Screening in US Women Living With Human Immunodeficiency Virus

Background: Primary human papillomavirus (HPV) screening (PHS) utilizes oncogenic human papillomavirus (oncHPV) testing as the initial cervical cancer screening method and typically, if positive, additional reflex-triage (eg, HPV16/18-genotyping, Pap testing). While US guidelines support PHS usage in the general population, PHS has been little studied in women living with HIV (WLWH). Methods: We enrolled n = 865 WLWH (323 from the Women's Interagency HIV Study [WIHS] and 542 from WIHS-affiliated colposcopy clinics). All participants underwent Pap and oncHPV testing, including HPV16/18-genotyping. WIHS WLWH who tested oncHPV[+] or had cytologic atypical squamous cells of undetermined significance or worse (ASC-US+) underwent colposcopy, as did a random 21% of WLWH who were oncHPV[-]/Pap[-] (controls). Most participants additionally underwent p16/Ki-67 immunocytochemistry. Results: Mean age was 46 years, median CD4 was 592 cells/μL, 95% used antiretroviral therapy. Seventy WLWH had histologically-determined cervical intraepithelial neoplasia grade 2 or greater (CIN-2+), of which 33 were defined as precancer (ie, [i] CIN-3+ or [ii] CIN-2 if concurrent with cytologic high grade squamous intraepithelial lesions [HSILs]). PHS had 87% sensitivity (Se) for precancer, 9% positive predictive value (PPV), and a 35% colposcopy referral rate (Colpo). "PHS with reflex HPV16/18-genotyping and Pap testing"had 84% Se, 16% PPV, 30% Colpo. PHS with only HPV16/18-genotyping had 24% Colpo. "Concurrent oncHPV and Pap Testing"(Co-Testing) had 91% Se, 12% PPV, 40% Colpo. p16/Ki-67 immunochemistry had the highest PPV, 20%, but 13% specimen inadequacy. Conclusions: PHS with reflex HPV16/18-genotyping had fewer unnecessary colposcopies and (if confirmed) could be a potential alternative to Co-Testing in WLWH