Inhibition of caveolin-1 restores myeloid cell function in human glioblastoma

Caveolin-1 promotes glioma progression and maintains its mitochondrial inhibition resistance

BACKGROUND

Glioma is a lethal brain cancer and lacking effective therapies. Challenges include no effective therapeutic target, intra- and intertumoral heterogeneity, inadequate effective drugs, and an immunosuppressive microenvironment, etc. Deciphering the pathogenesis of gliomas and finding out the working mechanisms are urgent and necessary for glioma treatment. Identification of prognostic biomarkers and targeting the biomarker genes will be a promising therapy.

METHODS

From our RNA-sequencing data of the oxidative phosphorylation (OXPHOS)-inhibition sensitive and OXPHOS-resistant cell lines, we found that the scaffolding protein caveolin 1 (CAV1) is highly expressed in the resistant group but not in the sensitive group. By comprehensive analysis of our RNA sequencing data, Whole Genome Bisulfite Sequencing (WGBS) data and public databases, we found that CAV1 is highly expressed in gliomas and its expression is positively related with pathological processes, higher CAV1 predicts shorter overall survival.

RESULTS

Further analysis indicated that (1) the differentiated genes in CAV1-high groups are enriched in immune infiltration and immune response; (2) CAV1 is positively correlated with tumor metastasis markers; (3) the methylation level of CAV1 promoters in glioma group is lower in higher stage than that in lower stage; (4) CAV1 is positively correlated with glioma stemness; (5) higher expression of CAV1 renders the glioma cells' resistant to oxidative phosphorylation inhibitors.

CONCLUSION

Therefore, we identified a key gene CAV1 and deciphered its function in glioma progression and prognosis, proposing that CAV1 may be a therapeutic target for gliomas.

Targeting Options of Tumor-Associated Macrophages (TAM) Activity in Gliomas

Tumor-associated macrophages (TAMs), the most plastic cells of the hematopoietic system, exhibit increased tumor-infiltrating properties and functional heterogeneity depending on tumor type and associated microenvironment. TAMs constitute a major cell type of cancer-related inflammation, commonly enhancing tumor growth. They are profoundly involved in glioma pathogenesis, contributing to many cancer hallmarks such as angiogenesis, survival, metastasis, and immunosuppression. Efficient targeting of TAMs presents a promising approach to tackle glioma progression. Several targeting options involve chemokine signaling axes inhibitors and antibodies, antiangiogenic factors, immunomodulatory molecules, surface immunoglobulins blockers, receptor and transcription factor inhibitors, as well as microRNAs (miRNAs), administered either as standalone or in combination with other conventional therapies. Herein, we provide a critical overview of current therapeutic approaches targeting TAMs in gliomas with the promising outcome.

Glioma-Associated Microglia Characterization in the Glioblastoma Microenvironment through A ‘Seed-and Soil’ Approach: A Systematic Review

Background and aim: Ever since the discovery of tumor-associated immune cells, there has been growing interest in the understanding of the mechanisms underlying the crosstalk between these cells and tumor cells. A “seed and soil” approach has been recently introduced to describe the glioblastoma (GBM) landscape: tumor microenvironments act as fertile “soil” and interact with the “seed” (glial and stem cells compartment). In the following article, we provide a systematic review of the current evidence pertaining to the characterization of glioma-associated macrophages and microglia (GAMs) and microglia and macrophage cells in the glioma tumor microenvironment (TME). Methods: An online literature search was launched on PubMed Medline and Scopus using the following research string: “((Glioma associated macrophages OR GAM OR Microglia) AND (glioblastoma tumor microenvironment OR TME))”. The last search for articles pertinent to the topic was conducted in February 2022. Results: The search of the literature yielded a total of 349 results. A total of 235 studies were found to be relevant to our research question and were assessed for eligibility. Upon a full-text review, 58 articles were included in the review. The reviewed papers were further divided into three categories based on their focus: (1) Microglia maintenance of immunological homeostasis and protection against autoimmunity; (2) Microglia crosstalk with dedifferentiated and stem-like glioblastoma cells; (3) Microglia migratory behavior and its activation pattern. Conclusions: Aggressive growth, inevitable recurrence, and scarce response to immunotherapies are driving the necessity to focus on the GBM TME from a different perspective to possibly disentangle its role as a fertile ‘soil’ for tumor progression and identify within it feasible therapeutic targets. Against this background, our systematic review confirmed microglia to play a paramount role in promoting GBM progression and relapse after treatments. The correct and extensive understanding of microglia–glioma crosstalk could help in understanding the physiopathology of this complex disease, possibly opening scenarios for improvement of treatments.

Overview of Crosstalk Between Multiple Factor of Transcytosis in Blood Brain Barrier

Blood brain barrier (BBB) conserves unique regulatory system to maintain barrier tightness while allowing adequate transport between neurovascular units. This mechanism possess a challenge for drug delivery, while abnormality may result in pathogenesis. Communication between vascular and neural system is mediated through paracellular and transcellular (transcytosis) pathway. Transcytosis itself showed dependency with various components, focusing on caveolae-mediated. Among several factors, intense communication between endothelial cells, pericytes, and astrocytes is the key for a normal development. Regulatory signaling pathway such as VEGF, Notch, S1P, PDGFβ, Ang/Tie, and TGF-β showed interaction with the transcytosis steps. Recent discoveries showed exploration of various factors which has been proven to interact with one of the process of transcytosis, either endocytosis, endosomal rearrangement, or exocytosis. As well as providing a hypothetical regulatory pathway between each factors, specifically miRNA, mechanical stress, various cytokines, physicochemical, basement membrane and junctions remodeling, and crosstalk between developmental regulatory pathways. Finally, various hypotheses and probable crosstalk between each factors will be expressed, to point out relevant research application (Drug therapy design and BBB-on-a-chip) and unexplored terrain.

The role of caveolin-1 in tumors of the brain - functional and clinical implications

BACKGROUND

Caveolin-1 (cav-1) is the major structural protein of caveolae, the flask-shaped invaginations of the plasma membrane mainly involved in cell signaling. Today, cav-1 is believed to play a role in a variety of disease processes including cancer, owing to the variations of its expression in association with tumor progression, invasive behavior, metastasis and therapy resistance. Since first detected in the brain, a number of studies has particularly focused on the role of cav-1 in the various steps of brain tumorigenesis. In this review, we discuss the different roles of cav-1 and its contributions to the molecular mechanisms underlying the pathobiology and natural behavior of brain tumors including glial, non-glial and metastatic subtypes. These contributions could be attributed to its co-localization with important players in tumorigenesis within the lipid-enriched domains of the plasma membrane. In that regard, the ability of cav-1 to interact with various cell signaling molecules as well as the impact of caveolae depletion on important pathways acting in brain tumor pathogenesis are noteworthy. We also discuss conversant causes hampering the treatment of malignant glial tumors such as limited transport of chemotherapeutics across the blood tumor barrier and resistance to chemoradiotherapy, by focusing on the molecular fundamentals involving cav-1 participation.

CONCLUSIONS

Cav-1 has the potential to pivot the molecular basis underlying the pathobiology of brain tumors, particularly the malignant glial subtype. In addition, the regulatory effect of cav-1-dependent and caveola-mediated transcellular transport on the permeability of the blood tumor barrier could be of benefit to overcome the restricted transport across brain barriers when applying chemotherapeutics. The association of cav-1 with tumors of the brain other than malignant gliomas deserves to be underlined, as well given the evidence suggesting its potential in predicting tumor grade and recurrence rates together with determining patient prognosis in oligodendrogliomas, ependymomas, meningiomas, vestibular schwannomas and brain metastases.

Caveolin-1, cancer and therapy resistance

Resistance of solid tumors to chemo- and radiotherapy remains a major obstacle in anti-cancer treatment. Herein, the membrane protein caveolin-1 (CAV1) came into focus as it is highly expressed in many tumors and high CAV1 levels were correlated with tumor progression, invasion and metastasis, and thus a worse clinical outcome. Increasing evidence further indicates that the heterogeneous tumor microenvironment, also known as the tumor stroma, contributes to therapy resistance resulting in poor clinical outcome. Again, CAV1 seems to play an important role in modulating tumor host interactions by promoting tumor growth, metastasis, therapy resistance and cell survival. However, the mechanisms driving stroma-mediated tumor growth and radiation resistance remain to be clarified. Understanding these interactions and thus, targeting CAV1 may offer a novel strategy for preventing cancer therapy resistance and improving clinical outcomes. In this review, we will summarize the resistance-promoting effects of CAV1 in tumors, and emphasize its role in the tumor-stroma communication as well as the resulting malignant phenotype of epithelial tumors.

Caveolin-1: a novel prognostic biomarker of radioresistance in cancer

PURPOSE

Caveolin-1 is a membrane protein highly expressed in many tumors and plays an important role in tumor progression and metastasis. This review describes the structure of the Caveolin-1 protein and its pre-clinical and clinical significance, demonstrating that Caveolin-1 is a novel biomarker for radioresistance which has the promising potential to improve the clinical outcome of cancer patients undergoing radiation treatment.

SUMMARY

Targeted radiation therapy has shown immense benefits for cancer treatment. However, one of the major challenges for effective clinical outcome of radiation therapy for cancer patients is the development of radioresistance during radiation treatment. As a consequence, radiation therapy becomes a less effective modality for successful clinical outcome. Furthermore, a radioresistant tumor has the ability to repair its genome, and therefore becomes more aggressive and metastasizes. The plausible mechanisms for tumor radioresistance include the rapid DNA repair, somatic mutations in tumor oncogenes, aberrant activation of kinase pathways, and changes in the tumor microenvironment including tumor hypoxia, tumor vasculature, and cancer stem cells. Caveolin-1 is significantly upregulated in certain cancer cells and aberrantly mediates downstream signaling mechanisms. Notably, numerous recent research reports have shown the role of Caveolin-1 in tumor radioresistance and poor treatment outcome. Thus, Caveolin-1 could be a novel prognostic biomarker to monitor tumor radioresistance in cancer patients undergoing radiation therapy.

CONCLUSIONS

Caveolin-1 has the promising potential to become a novel prognostic biomarker to monitor tumor radioresistance and radiation response specifically in the prostate, pancreas, and lung cancer.