Circular dorsal ruffles disturb the growth factor-induced PI3K-AKT pathway in hepatocellular carcinoma Hep3B cells

Macropinocytosis regulates cytokine expression through Erk signaling in LPS-stimulated macrophages

Macropinocytosis, a type of large-scale endocytosis process, is induced in macrophages by extracellular stimuli, including lipopolysaccharide (LPS). In addition to uptake function, emerging evidence supports a link between macropinocytosis and LPS-induced signal transduction. Following LPS stimulation, membrane ruffles are induced to form cup-like structures known as macropinocytic cups, a necessary precursory step for macropinocytosis. We have recently shown that Akt is activated at the cups and is an upstream regulator of the Iκ-B/NF-κB pathway implicated in the production of IL-1α and IL-6. Here, we further investigated the molecular mechanisms and show that the macropinocytic cups also regulated the Ras/Mek/Erk/c-Fos pathway to modulate IL-1β expression independently of the Akt pathway. In addition, we observed that the cup-dependent Akt pathway downregulated the expression of IL-10, in which the activation of the Erk pathway was critical. Taken together, we propose that macropinocytic cups separately modulate the Akt and Erk pathways in cytokine expression.Key words: macropinocytosis, Erk, IL-1β, IL-10.

Lycium barbarum L.: a potential botanical drug for preventing and treating retinal cell apoptosis

Retinal cell apoptosis is the primary pathological process in many retinal diseases, including retinitis pigmentosa and age-related macular degeneration, which can cause severe visual impairment and blindness. Lycium barbarum L., a traditional Chinese medicinal botanical drug, has a long history and extensive application in ophthalmic disease prevention and treatment. This study systematically reviewed the key active metabolites in L. barbarum L., including L. barbarum polysaccharides, carotenoids, and flavonoids, that exert retinal protective effects. A comprehensive analysis of the pharmacological effects and underlying molecular mechanisms of L. barbarum L. and its active metabolites in the prevention and treatment of retinal cell apoptosis, including essential aspects such as antioxidant activity, anti-inflammatory properties, autophagy regulation, and mitochondrial function preservation, is essential to establish a comprehensive and solid theoretical basis for further investigation of the medicinal value of L. barbarum L. in ophthalmology and provide a reference for future research directions.

Aberrant expression of GTPase-activating protein ARAP1 triggers circular dorsal ruffles associated with malignancy in hepatocellular carcinoma Hep3B cells

BACKGROUND

Circular dorsal ruffles (CDRs) are large and rounded membrane ruffles that function as precursors of macropinocytosis. We recently reported that CDRs form in Hep3B hepatocellular carcinoma (HCC) cells, but not in Huh7 and HepG2 HCC cells or LO2 cells, suggesting that an unknown molecular mechanism implicates CDRs in Hep3B malignancy through macropinocytosis uptake of excessive extracellular nutrients. In this study, we investigated the cellular role and the mechanism of CDRs in Hep3B cells by focusing on the GTPase-activating protein ARAP1.

METHODS

ARAP1 knock-out (KO) cells were generated. Confocal microscopy and high-resolution scanning electron microscopy (SEM) were used for identification of the target proteins and structure analysis, respectively. Proteasome inhibitor MG132, mitochondrial function inhibitor CCCP, ARF1 inhibitor Golgicide A, and macropinocytosis inhibitor EIPA were used to investigate the molecular mechanism. Cell proliferation and Transwell migration/invasion assays were used to investigate the role of ARAP1 in cellular malignancy.

RESULTS

ARAP1 was localized to CDRs, which had reduced size following ARAP1 KO. CDRs comprised small vertical lamellipodia, the expression pattern of which was disrupted in ARAP1 KO cells. Extracellular solute uptake, rate of cell growth, and malignant potential were attenuated in KO cells. ARAP1 was also localized to mitochondria in Hep3B cells but not in the control cell lines. Mitochondrial fission protein was increased in KO cells. CCCP treatment blocked CDRs in Hep3B cells but not in controls. Surprisingly, ARAP1 expression level in Hep3B cells was lower than in Huh7, HepG2, and LO2 cells. MG132 treatment increased the ARAP1 levels in Hep3B cells, but not in Huh7 cells, revealing that ARAP1 is actively degraded in Hep3B cells.

CONCLUSIONS

These results strongly suggest that the aberrant expression of ARAP1 in Hep3B cells modulates CDRs via mitochondrial function, thereby resulting in excess uptake of nutrients as an initial event in cancer development. Based on these findings, we propose that the molecular mechanisms underlying the formation of CDRs, focusing on ARAP1, may serve as an effective therapeutic target in some types of HCC and cancers.

Loss-of-function mutations of microRNA-142-3p promote ASH1L expression to induce immune evasion and hepatocellular carcinoma progression

BACKGROUND

Hepatocellular carcinoma (HCC) has been a pervasive malignancy throughout the world with elevated mortality. Efficient therapeutic targets are beneficial to treat and predict the disease. Currently, the exact molecular mechanisms leading to the progression of HCC are still unclear. Research has shown that the microRNA-142-3p level decreases in HCC, whereas bioinformatics analysis of the cancer genome atlas database shows the ASH1L expression increased among liver tumor tissues. In this paper, we will explore the effects and mechanisms of microRNA-142-3p and ASH1L affect the prognosis of HCC patients and HCC cell bioactivity, and the association between them.

AIM

To investigate the effects and mechanisms of microRNA-142-3p and ASH1L on the HCC cell bioactivity and prognosis of HCC patients.

METHODS

In this study, we grouped HCC patients according to their immunohistochemistry results of ASH1L with pathological tissues, and retrospectively analyzed the prognosis of HCC patients. Furthermore, explored the roles and mechanisms of microRNA-142-3p and ASH1L by cellular and animal experiments, which involved the following experimental methods: Immunohistochemical staining, western blot, quantitative real-time-polymerase chain reaction, flow cytometric analysis, tumor xenografts in nude mice, etc. The statistical methods involved in this study contained t-test, one-way analysis of variance, the χ 2 test, the Kaplan-Meier approach and the log-rank test.

RESULTS

In this study, we found that HCC patients with high expression of ASH1L possess a more recurrence rate as well as a decreased overall survival rate. ASH1L promotes the tumorigenicity of HCC and microRNA-142-3p exhibits reduced expression in HCC tissues and interacts with ASH1L through targeting the ASH1L 3'untranslated region. Furthermore, microRNA-142-3p promotes apoptosis and inhibits proliferation, invasion, and migration of HCC cell lines in vitro via ASH1L. For the exploration mechanism, we found ASH1L may promote an immunosuppressive microenvironment in HCC and ASH1L affects the expression of the cell junction protein zonula occludens-1, which is potentially relevant to the immune system.

CONCLUSION

Loss function of microRNA-142-3p induces cancer progression and immune evasion through upregulation of ASH1L in HCC. Both microRNA-142-3p and ASH1L can feature as new biomarker for HCC in the future.

Membrane Ruffles: Composition, Function, Formation and Visualization

Membrane ruffles are cell actin-based membrane protrusions that have distinct structural characteristics. Linear ruffles with columnar spike-like and veil-like structures assemble at the leading edge of cell membranes. Circular dorsal ruffles (CDRs) have no supporting columnar structures but their veil-like structures, connecting from end to end, present an enclosed ring-shaped circular outline. Membrane ruffles are involved in multiple cell functions such as cell motility, macropinocytosis, receptor internalization, fluid viscosity sensing in a two-dimensional culture environment, and protecting cells from death in response to physiologically compressive loads. Herein, we review the state-of-the-art knowledge on membrane ruffle structure and function, the growth factor-induced membrane ruffling process, and the growth factor-independent ruffling mode triggered by calcium and other stimulating factors, together with the respective underlying mechanisms. We also summarize the inhibitors used in ruffle formation studies and their specificity. In the last part, an overview is given of the various techniques in which the membrane ruffles have been visualized up to now.

Macropinocytic cups function as signal platforms for the mTORC2-AKT pathway to modulate LPS-induced cytokine expression in macrophages

Macropinocytosis is a large-scale endocytosis process primarily observed in phagocytes as part of their cellular function to ingest antigens. Once phagocytes encounter gram-negative bacteria, the receptor proteins identify lipopolysaccharides (LPSs), which trigger radical membrane ruffles that gradually change to cup-like structures. The open area of the cups closes to generate vesicles called macropinosomes. The target bacteria are isolated by the cups and engulfed by the cells as the cups close. In addition to its ingestion function, macropinocytosis also regulates the AKT pathway in macrophages. In the current study, we report that macropinocytic cups are critical for LPS-induced AKT phosphorylation (pAKT) and cytokine expression in macrophages. High-resolution scanning electron microscope observations detailed the macropinocytic cup structures induced by LPS stimulation. Confocal microscopy revealed that AKT and the kinase molecule mTORC2 were localized in the cups. The biochemical analysis showed that macropinocytosis inhibition blocked LPS-induced pAKT. RNA sequencing, quantitative polymerase chain reaction, and enzyme-linked immunosorbent assay analyses revealed that the inhibition of macropinocytosis or the AKT pathway causes a decrease in the expression of proinflammatory cytokines interlukin-6 and interlukin-1α. Moreover, activation of the transcription factor nuclear factor κB, which regulates the cytokine expression downstream of the AKT/IκB pathway, was hindered when macropinocytosis or AKT was inhibited. These results indicate that LPS-induced macropinocytic cups function as signal platforms for the AKT pathway to regulate the cytokine expression by modulating nuclear factor κB activity in LPS-stimulated macrophages. Based on these findings, we propose that macropinocytosis may be a good therapeutic target for controlling cytokine expression.

ATP2B4 is an essential gene for epidermal growth factor-induced macropinocytosis in A431 cells

Macropinocytosis (MPC) is a large-scale endocytosis pathway that involves actin-dependent membrane ruffle formation and subsequent ruffle closure to generate macropinosomes for the uptake of fluid-phase cargos. MPC is categorized into two types: constitutive and stimuli-induced. Constitutive MPC in macrophages relies on extracellular Ca2+ sensing by a calcium-sensing receptor. However, the link between stimuli-induced MPC and Ca2+ remains unclear. Here, we find that both intracellular and extracellular Ca2+ are required for epidermal growth factor (EGF)-induced MPC in A431 human epidermoid carcinoma cells. Through investigation of mammalian homologs of coelomocyte uptake defective (CUP) genes, we identify ATP2B4, encoding for a Ca2+ pump called the plasma membrane calcium ATPase 4 (PMCA4), as a Ca2+-related regulator of EGF-induced MPC. Knockout (KO) of ATP2B4, as well as depletion of extracellular/intracellular Ca2+, inhibited ruffle closure and macropinosome formation, without affecting ruffle formation. We demonstrate the importance of PMCA4 activity itself, independent of interactions with other proteins via its C-terminus known as a PDZ domain-binding motif. Additionally, we show that ATP2B4-KO reduces EGF-stimulated Ca2+ oscillation during MPC. Our findings suggest that EGF-induced MPC requires ATP2B4-dependent Ca2+ dynamics.

Construction of endothelial cell signatures for predicting the diagnosis, prognosis and immunotherapy response of bladder cancer via machine learning

We subtyped bladder cancer (BC) patients based on the expression patterns of endothelial cell (EC) -related genes and constructed a diagnostic signature and an endothelial cell prognostic index (ECPI), which are useful for diagnosing BC patients, predicting the prognosis of BC and evaluating drug sensitivity. Differentially expressed genes in ECs were obtained from the Tumour Immune Single-Cell Hub database. Subsequently, a diagnostic signature, a tumour subtyping system and an ECPI were constructed using data from The Cancer Genome Atlas and Gene Expression Omnibus. Associations between the ECPI and the tumour microenvironment, drug sensitivity and biofunctions were assessed. The hub genes in the ECPI were identified as drug candidates by molecular docking. Subtype identification indicated that high EC levels were associated with a worse prognosis and immunosuppressive effect. The diagnostic signature and ECPI were used to effectively diagnose BC and accurately assess the prognosis of BC and drug sensitivity among patients. Three hub genes in the ECPI were extracted, and the three genes had the closest affinity for doxorubicin and curcumin. There was a close relationship between EC and BC. EC-related genes can help clinicians diagnose BC, predict the prognosis of BC and select effective drugs.

GTPase-activating protein ARAP1 regulates circular dorsal ruffles as a nutrient uptake mechanism in the Hep3B hepatocellular carcinoma cell line

Circular dorsal ruffles (CDRs), large-scale rounded membrane ruffles, function as precursors of macropinocytosis. We recently reported that CDRs are exposed in the Hep3B hepatocellular carcinoma cell line, while not in other hepatocellular carcinoma cell lines, indicating that the CDRs in Hep3B are associated with malignant potential. In this study, we investigated the cellular function of CDRs in Hep3B cells by focusing on the molecular mechanisms of the GTPase-activating protein ARAP1. ARAP1 was localized to the CDRs, the sizes of which were reduced by deletion of this protein. High-resolution scanning electron micrographs revealed that CDRs comprise small vertical lamellipodia, the expression pattern of which was disrupted in ARAP1 KO cells. Extracellular solute uptake, rate of cell growth, and malignant potential were attenuated in the KO cells. ARAP1 is also localized in Hep3B cell mitochondria, although not in those of the Huh7 hepatocellular carcinoma cell line. On the basis of these findings, we propose that the aberrant expression of ARAP1 in Hep3B cells modulates CDRs, thereby resulting in an excess uptake of nutrients as an initial event in cancer development.

SUMMARY STATEMENT

ARAP1 regulates circular dorsal ruffles (CDRs) in the Hep3B HCC cell line and deletion of this protein attenuates malignant potential, thereby indicating the involvement of CDRs in cancer development.

Identification of circular dorsal ruffles as signal platforms for the AKT pathway in glomerular podocytes

Circular dorsal ruffles (CDRs) are rounded membrane ruffles induced by growth factors to function as precursors of the large-scale endocytosis called macropinocytosis. In addition to their role in cellular uptake, recent research using cell line systems has shown that CDRs/macropinocytosis regulate the canonical AKT-mTORC1 growth factor signaling pathway. However, as CDRs have not been observed in tissues, their physiological relevance has remained unclear. Here, utilizing ultrahigh-resolution scanning electron microscopy, we first report that CDRs are expressed in glomerular podocytes ex vivo and in vivo, and we visually captured the transformation process to macropinocytosis. Moreover, through biochemical and imaging analyses, we show that AKT phosphorylation localized to CDRs upstream of mTORC1 activation in podocyte cell lines and isolated glomeruli. These results demonstrate the physiological role of CDRs as signal platforms for the AKT-mTORC1 pathway in glomerular podocytes at the tissue level. As mTORC1 plays critical roles in podocyte metabolism, and aberrant activation of mTORC1 triggers podocytopathies, our results strongly suggest that targeting CDR formation could represent a potential therapeutic approach for these diseases.