Golgi-Localized PAQR4 Mediates Antiapoptotic Ceramidase Activity in Breast Cancer.

The metabolic network of sphingolipids plays important roles in cancer biology. Prominent sphingolipids include ceramides and sphingosine-1-phosphate that regulate multiple aspects of growth, apoptosis, and cellular signaling. Although a significant number of enzymatic regulators of the sphingolipid pathway have been described in detail, many remained poorly characterized. Here we applied a patient-derived systemic approach to identify and molecularly define progestin and adipoQ receptor family member IV (PAQR4) as a Golgi-localized ceramidase. PAQR4 was approximately 5-fold upregulated in breast cancer compared with matched control tissue and its overexpression correlated with disease-specific survival rates in breast cancer. Induction of PAQR4 in breast tumors was found to be subtype-independent and correlated with increased ceramidase activity. These findings establish PAQR4 as Golgi-localized ceramidase required for cellular growth in breast cancer. SIGNIFICANCE: Induction of and cellular dependency on de novo sphingolipid synthesis via PAQR4 highlights a central vulnerability in breast cancer that may serve as a viable therapeutic target.

AXL Targeting Abrogates Autophagic Flux and Induces Immunogenic Cell Death in Drug-Resistant Cancer Cells.

INTRODUCTION: Acquired cancer therapy resistance evolves under selection pressure of immune surveillance and favors mechanisms that promote drug resistance through cell survival and immune evasion. AXL receptor tyrosine kinase is a mediator of cancer cell phenotypic plasticity and suppression of tumor immunity, and AXL expression is associated with drug resistance and diminished long-term survival in a wide range of malignancies, including NSCLC. METHODS: We aimed to investigate the mechanisms underlying AXL-mediated acquired resistance to first- and third-generation small molecule EGFR tyrosine kinase inhibitors (EGFRi) in NSCLC. RESULTS: We found that EGFRi resistance was mediated by up-regulation of AXL, and targeting AXL reduced reactivation of the MAPK pathway and blocked onset of acquired resistance to long-term EGFRi treatment in vivo. AXL-expressing EGFRi-resistant cells revealed phenotypic and cell signaling heterogeneity incompatible with a simple bypass signaling mechanism, and were characterized by an increased autophagic flux. AXL kinase inhibition by the small molecule inhibitor bemcentinib or siRNA mediated AXL gene silencing was reported to inhibit the autophagic flux in vitro, bemcentinib treatment blocked clonogenicity and induced immunogenic cell death in drug-resistant NSCLC in vitro, and abrogated the transcription of autophagy-associated genes in vivo. Furthermore, we found a positive correlation between AXL expression and autophagy-associated gene signatures in a large cohort of human NSCLC (n = 1018). CONCLUSION: Our results indicate that AXL signaling supports a drug-resistant persister cell phenotype through a novel autophagy-dependent mechanism and reveals a unique immunogenic effect of AXL inhibition on drug-resistant NSCLC cells.