Subba Rao Gangi Setty

The nucleocapsid (N) protein of SARS‐CoV‐2 is central to viral assembly and replication. It binds the viral RNA to form a helical nucleocapsid and enables genome packaging and its release into host cells. Human heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1), one of the most abundant RNA‐binding proteins in eukaryotes, regulates key aspects of RNA metabolism, including splicing, transcription, localisation, and transport. Here, we report a direct physical interaction between the SARS‐CoV‐2 N protein and hnRNPA1, primarily mediated through their intrinsically disordered regions. Furthermore, we found that these proteins co‐phase separate in vitro and colocalise within stress granules in cells. In vivo studies reveal that hnRNPA1 suppresses viral replication, suggesting that the N protein–hnRNPA1 interaction plays an important role in modulating the viral life cycle.

Lysosome-related organelles (LROs) originate from the endo-lysosomal system with the contribution from the post-Golgi secretory pathway. While LROs share features with lysosomes, they contain unique cargo, morphologies and functions to support celltype specific functions. Around 15 bona fide LROs have been described in vertebrates, with skin melanosomes serving as a classical model. When their biogenesis, secretion, or function is disrupted, a range of genetic diseases can arise, underscoring their importance in physiology (Bowman et al., 2019;Delevoye et al., 2019). This special issue on the 'Biology of LROs' brings together diverse members of the LRO group, including melanosomes (from both skin epidermis and retinal pigment epithelium -RPE), epidermal lamellar bodies (LBs), platelets α-granules, Weibel-Palade bodies (WPBs) from vascular endothelial cells, and secretory granules (SGs) from mast cells. Beyond LROs, the issue broadens the view on endolysosomal-related processes, like autophagy and late endosomes/lysosomes dynamics, which help defining the cellular context of LRO specialization. In this editorial, we introduce the contributions that highlight the current understanding of LRO biology, from biogenesis to human genetic diseases associated with their dysfunction.The perspective by (Barral et al., 2025) reviews current insights into melanosome biogenesis. Melanocytes produce melanosomes, which synthesize and store melanin pigments before being transferred to keratinocytes, where they form supranuclear caps that shield genomic DNA from UV radiation-induced damage. Melanosome biogenesis follows a characterized sequential maturation process, and defects in this pathway underlie multiple hypopigmentation disorders, although therapeutic targeting remains elusive. Interestingly, melanosomes in epidermal melanocytes or RPE exhibit key differences. Unlike its skin counterparts, RPE melanosomes form early in the development, persist for life, and combine pigmentary role with lysosome-like degradative features. Finally, beyond skin and eye, the diversity of melanin types and melanocyte lineages underscores broader roles in cardiac, auditory and visual physiology.The mini-review by (Doncheva et al., 2025) further details distinctive features of RPE melanosomes compared with those of melanocytes. Although synthesized embryonically, RPE melanosomes follow biogenesis and trafficking pathways similar to skin melanosomes. Defects in genes regulating RPE melanosome positioning underlie genetic disorders, while age-related melanosome dysfunction contributes to retinal degenerative diseases such as age-related macular degeneration (AMD). RPE melanosomes form membrane contacts with mitochondria and/or the endoplasmic reticulum, enabling Ca 2+ exchange and reactive oxygen species quenching, and thus cellular homeostasis. In parallel, RPE lysosomes facilitate the digestion of photoreceptor outer segments, with failure in this pathway resulting in the accumulation of the toxic ageing pigment lipofuscin. Fusion of lipofuscin-containing lysosomes with melanosomes form melanolipofuscin, promoting melanin-dependent lipofuscin degradation through chemiexcitation. Beyond these roles, RPE melanosomes also exert protective effects in AMD, highlighting how long-lived RPE melanosomes link cell-type specific functions to retinal diseases.Focusing on platelets, the mini-review by (Ambrosio and Di Pietro, 2025) discusses the biogenesis of α-granules, a major LRO derived from megakaryocytes (MKs). These granules are central to hemostasis and also store factors involved in angiogenesis and inflammation. As with other LROs, α-granule formation relies on sorting and recycling endosomes, which act as membrane transport intermediates, a process well illustrated using induced pluripotent stem cell -derived MKs. This cellular system has become a powerful model for dissecting how ubiquitous membrane trafficking machinery is adapted for α-granule biogenesis. Such specialization could rely on the MK-enriched protein NBEAL2, which emerges as a key adaptor coordinating endosomal membrane dynamics and cargo sorting. Together, mutations in several of these components cause human bleeding disorders.The review by (Leprince and Simon, 2025) focuses on epidermal LBs, the LROs in keratinocytes of the stratum granulosum that are essential for skin barrier function. LBs store lipids, proteases, and antimicrobial peptides, which together maintain the hydrophobic properties, structural integrity, and defense capacity of the uppermost skin layer, the stratum corneum. LB dysfunction leads to barrier defects and an ichthyotic phenotype marked by dry, thickened, and scaly skin. Despite their importance, the molecular mechanisms regulating LB biogenesis and trafficking remain poorly characterized. As for other LROs, endosomal components such as Rab11a, Myosin Vb and the CHEVI tethering complex have been implicated in LB trafficking. Further work is therefore needed to clarify LB biology and the etiology of diseases involving their dysfunction, including atopic dermatitis and active plaque psoriasis.The perspective by (Mahanty, 2025) further highlights the scarce knowledge on the biogenesis mechanisms of LBs, emphasizing their origin at the trans-Golgi network (TGN), and discusses the models for LB structure/morphology and secretion mechanisms. Furthermore, it pinpoints candidate regulators of LB biogenesis and trafficking based on evidence from disease models. Finally, it discusses the limitations of current models used to study LB biology and underscores the need to develop advanced models, such as 3D skin organoids, that can be manipulated and accurately reflect the differentiation state of stratum granulosum keratinocytes.The mini-review by (Terglane and Gerke, 2025) addresses the biogenesis, transport, and regulated secretion of WPBs, the specialized LROs of vascular endothelial cells. Unlike most LROs, WPBs...

Lysosome-related organelles (LROs) encompass specialized intracellular compartments that share features with lysosomes while fulfilling distinct physiological roles, with melanosomes representing the best-studied example. Melanosome biogenesis relies on coordinated trafficking, sorting, and membrane remodeling mechanisms that diverge from the canonical endolysosomal pathways. These organelles ultimately serve as the primary sites of melanin synthesis and deposition. In the skin, melanin is produced by melanocytes and transferred to keratinocytes, where it achieves its essential photoprotective role. Melanin is a remarkably diverse and ancient polymer, with eumelanin, pheomelanin, and neuromelanin constituting the major mammalian forms. Understanding melanin biology also requires tracing the origins of melanocytes, which were once thought to derive exclusively from the neural crest but are now known to arise from multiple embryonic lineages. This expanded view of melanocyte ontogeny has revealed unexpected pigment cell populations in several internal organs. Beyond these developmental aspects, melanin performs multifaceted physiological functions that extend far beyond photoprotection of the skin. Here, we discuss the current knowledge on the origin of melanosomes from endosomal precursors, the transfer of melanin from melanocytes to keratinocytes, and its fate in these recipient cells within the epidermis. Additionally, the intriguing mysteries surrounding melanosomes in the retinal pigment epithelium are addressed, as well as the broader diversity, origins, and physiological roles of melanin in other cell types. Taken together, these perspectives highlight the melanosome as both a model LRO and an organellar hub for deciphering melanin diversity, cellular origins, and the wide-ranging physiological roles of this pigment in vertebrate biology.

Lysosome exocytosis is one of the critical functions of lysosomes in maintaining cellular homeostasis and plasma membrane (PM) repair. At the basal level, the SNAREs (soluble-N-ethylmaleimide-sensitive-factor accessory-protein receptors) regulating the lysosome fusion with the cell surface have been poorly defined. Here, we identified a Qa-SNARE STX1A, localized majorly to lysosomes and a cohort to the PM in HeLa cells. Overexpression of GFP-STX1A in HeLa cells causes decreased lysosome number and their peripheral dispersion. However, STX1A knockdown in HeLa cells displayed an accumulation of lysosomes beneath the cell surface with reduced lysosome exocytosis. Consistently, TIRF imaging microscopy demonstrated an enhanced enrichment of LAMP1-positive vesicles at the cell surface in STX1A-depleted compared with control cells. Moreover, STX1A depletion reduces proteolytic activity without affecting the lysosome content or acidity. Additionally, these cells showed enhanced lysosome dispersion and autolysosome accumulation. Functionally, GFP-STX1A also localizes to LLOMe-induced GAL3-positive damaged lysosomes and reduces their number by enhancing exocytosis. Biochemically, STX1A forms a SNARE complex with SNAP23 or SNAP25 (Qbc) and VAMP2 (R), and their knockdown in HeLa cells mimics the STX1A-depletion phenotypes. Overall, these studies demonstrate a unique function of STX1A in regulating lysosomal exocytosis by localizing to these degradative organelles.

The nucleocapsid (N) protein of SARS-CoV-2 is central to viral assembly and replication. It binds viral RNA to form a helical nucleocapsid and enabling genome packaging and release into host cells. Human hnRNPA1, one of the most abundant RNA-binding proteins in eukaryotes, regulates key aspects of RNA metabolism, including splicing, transcription, localisation, and transport. Here, we report a direct physical interaction between SARS-CoV-2 N protein and hnRNPA1 with moderate affinity (Kd ∼ 0.18 μM), primarily mediated through their intrinsically disordered regions. Furthermore, we found that these proteins co-phase separate in vitro and co-localise within stress granules in cells. In vivo studies reveal that hnRNPA1 suppresses viral replication, suggesting that the N protein – hnRNPA1 interaction plays an important role in modulating the viral life cycle.

Arf‐like GTPases (Arls) regulate membrane trafficking and cytoskeletal organization. Genetic studies predicted a role for Arl15 in type‐2 diabetes, insulin resistance, adiposity, and rheumatoid arthritis. Cell biological studies implicated Arl15 in regulating various cellular processes, including magnesium homeostasis and TGFβ signaling. However, the role of Arl15 in vesicular transport is poorly defined. We evaluated the function of Arl15 using techniques to quantify cargo trafficking to mechanobiology. Fluorescence microscopy of stably expressing Arl15‐GFP HeLa cells showed its localization primarily to the Golgi and cell surface. The depletion of Arl15 causes the mislocalization of selective Golgi cargo, such as caveolin‐2 and STX6, in the cells. Consistently, expression of GTPase‐independent dominant negative mutants of Arl15 (Arl15^{V80A,A86L,E122K} and Arl15^C22Y,C23Y) results in mislocalization of caveolin‐2 and STX6 from the Golgi. However, the localization of Arl15 to the Golgi is dependent on its palmitoylation and Arf1‐dependent Golgi integrity. At the cellular level, Arl15 depleted cells display enhanced cell spreading and adhesion strength. Traction force microscopy experiments revealed that Arl15 depleted cells exert higher tractions and generate multiple focal adhesion points during the initial phase of cell adhesion compared to control cells. Collectively, these studies implicate a functional role for Arl15 in regulating cargo transport from the Golgi to regulate cell surface processes.

Intracellular pathogens rely on manipulating host endocytic pathways to ensure survival. Legionella and Chlamydia exploit host SNARE proteins, with Legionella cleaving syntaxin 17 (STX17) and Chlamydia interacting with VAMP8 and VAMP7. Similarly, Salmonella targets the host's endosomal fusion machinery, using SPI effectors like SipC and SipA to interact with syntaxin 6 (STX6) and syntaxin 8 (STX8), respectively, maintaining its vacuolar niche. Recent evidence highlights syntaxin 7 (STX7), a Qa‐SNARE involved in endo‐lysosomal fusion, as a potential Salmonella target. BioID screening revealed STX7 interactions with SPI‐2 effectors SifA and SopD2, suggesting a critical role in Salmonella pathogenesis. We investigated the role of STX7 in Salmonella‐containing vacuole (SCV) biogenesis and pathogenesis in macrophages and epithelial cells. Our findings indicate that STX7 levels and localization differ between these cell types during infection, reflecting the distinct survival strategies of Salmonella. Live cell imaging showed that STX7 is recruited to SCVs at different infection stages, with significantly altered distribution in HeLa cells at the late stage of infection. STX7 knockdown resulted in reduced bacterial survival, which was rescued upon overexpression of STX7 in both HeLa and RAW264.7 cells, suggesting Salmonella hijacks STX7 to evade lysosomal fusion and secure nutrients for intracellular replication. These results underscore the essential role of STX7 in maintaining SCVs and facilitating Salmonella survival. Further, the temporal expression of STX7 adaptor/binding partners in macrophages showed dynamic interactions with STX7 facilitating Salmonella infection and survival in host cells. Together, our study highlights STX7 as a critical host factor exploited by Salmonella, providing insights into the molecular mechanisms underlying its pathogenesis in macrophages and epithelial cells. These findings may inform strategies for targeting host‐pathogen interactions to combat Salmonella infections.

Lysosome exocytosis is one of the critical functions of lysosomes in maintaining cellular homeostasis and plasma membrane repair. The SNAREs regulating the lysosome fusion with the cell surface at the basal level have been poorly defined. Here, we identified STX1A, a Qa- SNARE localized majorly to lysosomes and a cohort to the plasma membrane in HeLa cells. Overexpression of GFP-STX1A in HeLa cells causes decreased lysosome number and their peripheral dispersion. In line, STX1A knockdown resulted in the accumulation of lysosomes beneath the cell surface and showed reduced lysosome exocytosis in HeLa cells. TIRF imaging microscopy demonstrated an enhanced enrichment of LAMP1-positive vesicles at the cell surface in STX1A depleted compared to control cells. Moreover, STX1A depletion reduces the proteolytic activity without affecting the lysosome content or acidity and increases peripheral lysosome dispersion compared to control cells. Consistently, these cells display an enhanced number of autophagosomes and accumulate autolysosomes. Functionally, GFP-STX1A also localizes to LLOMe-induced GAL3-positive damaged lysosomes and reduces their number by enhancing exocytosis. Biochemically, STX1A forms a SNARE complex with SNAP23 or SNAP25 (Qbc) and VAMP2 (R), and their knockdown in HeLa cells mimics the STX1A- depletion phenotypes. Overall, these studies demonstrate a unique function of STX1A in regulating lysosomal exocytosis by localizing to these degradative organelles. Key points STX1A localizes to lysosomes and plasma membrane in HeLa cells STX1A overexpression decreases the lysosome number and their dispersion and facilitates the exocytosis of LLOMe-damaged lysosomes STX1A knockdown enhances the lysosome dispersion, accumulates beneath the cell surface in HeLa cells, and displays decreased lysosome exocytosis STX1A biochemically interacts with SNAP23/SNAP25, VAMP2 and their individual knockdown phenocopy their phenotypes each other

Intracellular pathogens rely on manipulating host endocytic pathways to ensure survival. Legionella and Chlamydia exploit host SNARE proteins, with Legionella cleaving syntaxin 17 (STX17) and Chlamydia interacting with VAMP8 and VAMP7. Similarly, Salmonella targets the host’s endosomal fusion machinery, using SPI effectors like SipC and SipA to interact with syntaxin 6 (STX6) and syntaxin 8 (STX8), respectively, maintaining its vacuolar niche. Recent evidence highlights syntaxin 7 (STX7), a Qa-SNARE involved in endo-lysosomal fusion, as a potential Salmonella target. BioID screening revealed STX7 interactions with SPI-2 effectors SifA and SopD2, suggesting a critical role in Salmonella pathogenesis. We investigated the role of STX7 in Salmonella -containing vacuole (SCV) biogenesis and pathogenesis in macrophages and epithelial cells. Our findings indicate that STX7 levels and localization differ between these cell types during infection, reflecting the distinct survival strategies of Salmonella . Live cell imaging showed that STX7 is recruited to SCVs at different infection stages, with significantly altered distribution in HeLa cells at the late stage of infection. STX7 knockdown resulted in reduced bacterial survival, which was rescued upon overexpression of STX7 in both HeLa and RAW264.7 cells, suggesting Salmonella hijacks STX7 to evade lysosomal fusion and secure nutrients for intracellular replication. These results underscore the essential role of STX7 in maintaining SCVs and facilitating Salmonella survival. Further, the temporal expression of STX7 adaptor/binding partners in macrophages showed dynamic interactions with STX7 facilitating Salmonella infection and survival in host cells. Together, our study highlights STX7 as a critical host factor exploited by Salmonella , providing insights into the molecular mechanisms underlying its pathogenesis in macrophages and epithelial cells. These findings may in form strategies for targeting host-pathogen interactions to combat Salmonella infections.

Fission and fusion processes maintain the mitochondrial dynamics at a steady state and are altered during various cellular stresses. The mechanisms that regulate mitochondrial dynamics during ER stress are critically unknown. Here, we identified a dual specificity phosphatase DUSP28 with a novel role in regulating mitochondrial morphology during ER stress. Cytosolic DUSP28 translocates to mitochondria during ER stress via PERK activation and further promotes mitochondrial fission in a Drp1-dependent manner. Interestingly, the knockdown of DUSP28 activates PERK signaling and enhances ER expansion following mitochondrial elongation by enhancing S637 phosphorylation of Drp1. Overexpression of DUSP28-GFP could not rescue the loss of Drp1 function, indicating its necessity for mitochondrial fission. Further, the presence of DUSP28 on mitochondria prevents Parkin recruitment during CCCP-induced mitochondrial damage and follows STX17-dependent mitophagy. These findings illustrate the novel crosstalk between ER stress and DUSP28 phosphatase in maintaining the mitochondrial dynamics to sustain cellular stress. Key points PERK activation translocates cytosolic DUSP28 to mitochondria DUSP28 mediates Drp1-dependent mitochondrial fission DUSP28 phosphorylation status determines its localization and function DUSP28 inhibits Parkin recruitment to mitochondria upon CCCP treatment and follows STX17-mediated mitophagy