Organelle homeostasis: from cellular mechanisms to disease

Deciphering melanophagy: role of the PTK2-ITCH-MLANA-OPTN cascade on melanophagy in melanocytes

Melanosomes play a pivotal role in skin color and photoprotection. In contrast to the well-elucidated pathway of melanosome biogenesis, the process of melanosome degradation, referred to as melanophagy, is largely unexplored. Previously, we discovered that 3,4,5-trimethoxycinnamate thymol ester (TCTE) effectively inhibits skin pigmentation by activating melanophagy. In this study, we discovered a new regulatory signaling cascade that controls melanophagy in TCTE-treated melanocytes. ITCH (itchy E3 ubiquitin protein ligase) facilitates ubiquitination of the melanosome membrane protein MLANA (melan-A) during TCTE-induced melanophagy. This ubiquitinated MLANA is then recognized by an autophagy receptor protein, OPTN (optineurin). Additionally, a phospho-kinase antibody array revealed that TCTE activates PTK2 (protein tyrosine kinase 2), which phosphorylates ITCH, enhancing the ubiquitination of MLANA. Furthermore, inhibition of either PTK2 or ITCH disrupts the ubiquitination of MLANA and the MLANA-OPTN interaction in TCTE-treated cells. Taken together, our findings highlight the critical role of the PTK2-ITCH-MLANA-OPTN cascade in orchestrating melanophagy progression.Abbreviations: α-MSH: alpha-melanocyte-stimulating hormone; dichlone: 2,3-dichloro-1,4-naphthoquinone; ITCH: itchy E3 ubiquitin protein ligase; MITF: melanocyte inducing transcription factor; MLANA: melan-A; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; PINK1: PTEN induced kinase 1; PTK2: protein tyrosine kinase 2; SQSTM1/p62: sequestosome 1; TCTE: 3,4,5-trimethoxycinnamate thymol ester; TPC2: two pore segment channel 2; VDAC1: voltage dependent anion channel 1.

Sulfur-based fluorescent probes for biological analysis: A review

The widespread adoption of small-molecule fluorescence detection methodologies in scientific research and industrial contexts can be ascribed to their inherent merits, including elevated sensitivity, exceptional selectivity, real-time detection capabilities, and non-destructive characteristics. In recent years, there has been a growing focus on small-molecule fluorescent probes engineered with sulfur elements, aiming to detect a diverse array of biologically active species. This review presents a comprehensive survey of sulfur-based fluorescent probes published from 2017 to 2023. The diverse repertoire of recognition sites, including but not limited to N, N-dimethylthiocarbamyl, disulfides, thioether, sulfonyls and sulfoxides, thiourea, thioester, thioacetal and thioketal, sulfhydryl, phenothiazine, thioamide, and others, inherent in these sulfur-based probes markedly amplifies their capacity for detecting a broad spectrum of analytes, such as metal ions, reactive oxygen species, reactive sulfur species, reactive nitrogen species, proteins, and beyond. Owing to the individual disparities in the molecular structures of the probes, analogous recognition units may be employed to discern diverse substrates. Subsequent to this classification, the review provides a concise summary and introduction to the design and biological applications of these probe molecules. Lastly, drawing upon a synthesis of published works, the review engages in a discussion regarding the merits and drawbacks of these fluorescent probes, offering guidance for future endeavors.

Membrane tension sensing formin-binding protein 1 is a neuronal nutrient stress-responsive Golgiphagy receptor

BACKGROUND

Nutrient stress-responsive neuronal homeostasis relies on intricate autophagic mechanisms that modulate various organelle integrity and function. The selective autophagy of the Golgi, known as Golgiphagy, regulates secretory processes by modulating vesicle trafficking during nutrient starvation.

RESULTS

In this study, we explored a genetic screen of BAR-domain-containing proteins to elucidate the role of formin-binding protein 1 (FNBP1) as a Golgiphagy receptor in modulating Golgi dynamics in response to varying nutrient availability in neurons. Mapping the systems network of FNBP1 and its interacting proteins reveals the putative involvement of FNBP1 in autophagy and Golgi-associated processes. While nutrient depletion causes Golgi fragmentation, FNBP1 preferentially localizes to the fragmented Golgi membrane through its 284FEDYTQ289 motif during nutrient stress. Simultaneously, FNBP1 engages in molecular interactions with LC3B through a conserved 131WKQL134 LC3 interacting region, thereby sequestering the fragmented Golgi membrane in neuronal autophagosomes. Increased aggregation of GM130, abnormal clumping of RAB11-positive secretory granules, and enhanced senescent death of FNBP1-depleted starved neurons indicate disruptions of neuronal homeostasis under metabolic stress.

CONCLUSION

The identification of FNBP1 as a nutrient stress-responsive Golgiphagy receptor expands our insights into the molecular mechanisms underlying Golgiphagy, establishing the crosstalk between nutrient sensing and membrane tension-sensing regulatory autophagic processes of Golgi turnover in neurons.

Toosendanin Induces Lung Squamous Cell Carcinoma Cell Apoptosis and Inhibits Tumor Progression via the BNIP3/AMPK Signaling Pathway

Lung squamous cell carcinoma (LUSC) is the second most common type of non-small cell lung cancer. Toosendanin can target critical cancer cell survival and proliferation. However, the function of toosendanin in LUSC is limited. Cancer cell proliferative capacity is detected using cell morphology, colony formation, and flow cytometry. The invasiveness of the cells is detected by a Transwell assay, western blotting, and RT-qPCR. Nude mice are injected with H226 (1×106) and received an intraperitoneal injection of toosendanin every 2 days for 21 days. RNA sequence transcriptome analysis is performed on toosendanin-treated cells to identify target genes and signaling pathways. With increasing concentrations of toosendanin, the rate of cell proliferation decreases and apoptotic cells increases. The number of migrated cells significantly reduces and epithelial-mesenchymal transition is reversed. Injection of toosendanin in nude mice leads to a reduction in tumor volume, weight, and the number of metastatic tumors. Furthermore, KEGG shows that genes related to the AMPK pathway are highly enriched. BNIP3 is the most differentially expressed gene, and its expression along with phosphorylated-AMPK significantly increases in toosendanin-treated cells. Toosendanin exerts anticancer effects, induces apoptosis in LUSC cells, and inhibits tumor progression via the BNIP3/AMPK signaling pathway.

The FEBS Journal in 2023: building back better

The FEBS Journal publishes high impact research on diverse topics in the life sciences, with a focus on molecular mechanisms underpinning biological processes. Here, Editor-in-Chief Seamus Martin discusses highlights of the journal from the past year and gives a glimpse into what's in store for 2023.