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The apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1) is an essential enzyme of the base excision repair pathway of non‐distorting DNA lesions. In response to genotoxic treatments, APE1 is highly secreted (sAPE1) in association with small‐extracellular vesicles (EVs). Interestingly, its presence in the serum of patients with hepatocellular or non‐small‐cell‐lung cancers may represent a prognostic biomarker. The mechanism driving APE1 to associate with EVs is unknown, but is of paramount importance in better understanding the biological roles of sAPE1. Because APE1 lacks an endoplasmic reticulum‐targeting signal peptide, it can be secreted through an unconventional protein secretion endoplasmic reticulum–Golgi‐independent pathway, which includes an endosome‐based secretion of intraluminal vesicles, mediated by multivesicular bodies (MVBs). Using HeLa and A549 cell lines, we investigated the role of endosomal sorting complex required for transport protein pathways (either‐dependent or ‐independent) in the constitutive or trichostatin A‐induced secretion of sAPE1, by means of manumycin A and GW 4869 treatments. Through an in‐depth biochemical analysis of late‐endosomes (LEs) and early‐endosomes (EEs), we observed that the distribution of APE1 on density gradient corresponded to that of LE–CD63, LE–Rab7, EE–EEA1 and EE–Rab 5. Interestingly, the secretion of sAPE1, induced by cisplatin genotoxic stress, involved an autophagy‐based unconventional secretion requiring MVBs. The present study enlightens the central role played by MVBs in the secretion of sAPE1 under various stimuli, and offers new perspectives in understanding the biological relevance of sAPE1 in cancer cells. [ABSTRACT FROM AUTHOR]

Caveolin‐1 (Cav‐1) is a fundamental constituent of caveolae, whose functionality and structure are strictly dependent on cholesterol. In this work the U18666A inhibitor was used to study the role of cholesterol transport in the endosomal degradative‐secretory system in a metastatic human melanoma cell line (WM266‐4). We found that U18666A induces a shift of Cav‐1 from the plasma membrane to the endolysosomal compartment, which is involved, through Multi Vesicular Bodies (MVBs), in the formation and release of small extracellular vesicles (sEVs). Moreover, this inhibitor induces an increase in the production of sEVs with chemical–physical characteristics similar to control sEVs but with a different protein composition (lower expression of Cav‐1 and increase of LC3II) and reduced transfer capacity on target cells. Furthermore, we determined that U18666A affects mitochondrial function and also cancer cell aggressive features, such as migration and invasion. Taken together, these results indicate that the blockage of cholesterol transport, determining the internalization of Cav‐1, may modify sEVs secretory pathways through an increased fusion between autophagosomes and MVBs to form amphisome, which in turn fuses with the plasma membrane releasing a heterogeneous population of sEVs to maintain homeostasis and ensure correct cellular functionality. [ABSTRACT FROM AUTHOR]

Inflammatory conditions, together with oxidative stress and cytokine storm, represent the main pathogenetic features of the ongoing global pandemic coronavirus disease 2019 (COVID-19), caused by the recently discovered coronavirus SARS-CoV-2. A typical feature of COVID-19 is the oxidative stress conditions, created in the SARS-CoV-2-infected cells by an excessive activation of the immune response, leading to an exacerbated inflammatory responses described as "cytokine storm" and culminating in mitochondrial dysfunctions. Thus, investigations on the potential modulation of immune and inflammatory responses in SARS-CoV-2-infected cells by mitomiR could be interesting and helpful to better elucidate the molecular mechanisms involved in immune evasion by SARS-CoV-2 and in COVID-19 pathogenesis. [Extracted from the article]

Caveolae have been indicated as a center of cytoskeleton regulation for Src kinase/Rho GTPase signaling. In addition, Src recruitment on intact cortical actin cytoskeleton appears to be required for bFGF/FGFR signal activation. Recently, we established a relationship between caveolin-1 (Cav-1) expression and cell migration in human malignant melanoma, constitutively activated by a bFGF autoregulatory loop. This work intends to investigate whether caveolae's asset, through bFGF/FGFR/c-Src/Rho signaling, could be related to melanoma cell anchorage. Accordingly, we revealed the existence of a FGFR/Src kinase pathway in Cav-1 enriched detergent-resistant membranes (DRMs) of Me665/1 metastatic melanoma cells, as confirmed by FGFR silencing. Moreover, we determined the expression and phosphorylation levels of Cav-1/Src/Erk signal pathway as a function of FGFR activation and cell density. A sucrose density gradient ultracentrifugation was employed to monitor Cav-1 membrane association and buoyancy in Me665/1 cells treated for actin fragmentation or for altered phosphorylation signals. As a result, melanoma cells show remarkable resistance to Cav-1 disassembly, together with persisting cell signal activity, being Src and Cav-1 crucial modulators of Rho GTPases. In conclusion, our study primarily highlights, in a metastatic melanoma cell line expressing caveolin, the circumstances whereby caveola structural and functional endurance enables the FGFR/Src/Rho GTPases pathway to keep on cell progression. [ABSTRACT FROM AUTHOR]

Presents a study which investigated whether flotillin-a and caveolin-3 coordinately modulate the insulin-stimulated signaling cascades that lead to the translocation of GLUT4 to the plasma membrane in skeletal muscle cells. Activation of the PI3K/Akt pathway; Reduction in glucose uptake due to lack of caveolin-3; Movement of caveolin-3 from the plasma membrane toward the cytosplasm; Promotion of the movement of the insulin receptor from caveolin-3-containing domains to flotillin-1-containing domains by insulin.