NGFR regulates stromal cell activation in germinal centers

Nerve growth factor receptor (NGFR) is expressed by follicular dendritic cells (FDCs). However, the role of NGFR in the humoral response is not well defined. Here, we study the effect of Ngfr loss on lymph node organization and function, demonstrating that Ngfr depletion leads to spontaneous germinal center (GC) formation and an expansion of the GC B cell compartment. In accordance with this effect, stromal cells are altered in Ngfr-/- mice with a higher frequency of FDCs, characterized by CD21/35, MAdCAM-1, and VCAM-1 overexpression. GCs are located ectopically in Ngfr-/- mice, with lost polarization together with impaired high-affinity antibody production and an increase in circulating autoantibodies. We observe higher levels of autoantibodies in Bcl2 Tg/Ngfr-/- mice, concomitant with a higher incidence of autoimmunity and lower overall survival. Our work shows that NGFR is involved in maintaining GC structure and function, participating in GC activation, antibody production, and immune tolerance.

Melanoma-derived small extracellular vesicles induce lymphangiogenesis and metastasis through an NGFR-dependent mechanism

Secreted extracellular vesicles (EVs) influence the tumor microenvironment and promote distal metastasis. Here, we analyzed the involvement of melanoma-secreted EVs in lymph node pre-metastatic niche formation in murine models. We found that small EVs (sEVs) derived from metastatic melanoma cell lines were enriched in nerve growth factor receptor (NGFR, p75NTR), spread through the lymphatic system and were taken up by lymphatic endothelial cells, reinforcing lymph node metastasis. Remarkably, sEVs enhanced lymphangiogenesis and tumor cell adhesion by inducing ERK kinase, nuclear factor (NF)-κB activation and intracellular adhesion molecule (ICAM)-1 expression in lymphatic endothelial cells. Importantly, ablation or inhibition of NGFR in sEVs reversed the lymphangiogenic phenotype, decreased lymph node metastasis and extended survival in pre-clinical models. Furthermore, NGFR expression was augmented in human lymph node metastases relative to that in matched primary tumors, and the frequency of NGFR⁺ metastatic melanoma cells in lymph nodes correlated with patient survival. In summary, we found that NGFR is secreted in melanoma-derived sEVs, reinforcing lymph node pre-metastatic niche formation and metastasis.

Specific Activation of the CD271 Intracellular Domain in Combination with Chemotherapy or Targeted Therapy Inhibits Melanoma Progression

CD271 (NGFR) is a neurotrophin receptor that belongs to the tumor necrosis receptor (TNFR) family. Upon ligand binding, CD271 can mediate either survival or cell death. Although the role of CD271 as a marker of tumor-initiating cells is still a matter of debate, its role in melanoma progression has been well documented. Moreover, CD271 has been shown to be upregulated after exposure to both chemotherapy and targeted therapy. In this study, we demonstrate that activation of CD271 by a short β-amyloid-derived peptide (Aβ^(25-35)) in combination with either chemotherapy or MAPK inhibitors induces apoptosis in 2D and 3D cultures of eight melanoma cell lines. This combinatorial treatment significantly reduced metastasis in a zebrafish xenograft model and led to significantly decreased tumor volume in mice. Administration of Aβ^(25-35) in ex vivo tumors from immunotherapy- and targeted therapy-resistant patients significantly reduced proliferation of melanoma cells, showing that activation of CD271 can overcome drug resistance. Aβ^(25-35) was specific to CD271-expressing cells and induced CD271 cleavage and phosphorylation of JNK (pJNK). The direct protein-protein interaction of pJNK with CD271 led to PARP1 cleavage, p53 and caspase activation, and pJNK-dependent cell death. Aβ^(25-35) also mediated mitochondrial reactive oxygen species (mROS) accumulation, which induced CD271 overexpression. Finally, CD271 upregulation inhibited mROS production, revealing the presence of a negative feedback loop in mROS regulation. These results indicate that targeting CD271 can activate cell death pathways to inhibit melanoma progression and potentially overcome resistance to targeted therapy. SIGNIFICANCE: The discovery of a means to specifically activate the CD271 death domain reveals unknown pathways mediated by the receptor and highlights new treatment possibilities for melanoma.

Could Extracellular Vesicles Contribute to Generation or Awakening of "Sleepy" Metastatic Niches?

Pre-metastatic niches provide favorable conditions for tumor cells to disseminate, home to and grow in otherwise unfamiliar and distal microenvironments. Tumor-derived extracellular vesicles are now recognized as carriers of key messengers secreted by primary tumors, signals that induce the formation of pre-metastatic niches. Recent evidence suggests that tumor cells can disseminate from the very earliest stages of primary tumor development. However, once they reach distal sites, tumor cells can persist in a dormant state for long periods of time until their growth is reactivated and they produce metastatic lesions. In this new scenario, the question arises as to whether extracellular vesicles could influence the formation of these metastatic niches with dormant tumor cells? (here defined as "sleepy niches"). If so, what are the molecular mechanisms involved? In this perspective-review article, we discuss the possible influence of extracellular vesicles in early metastatic dissemination and whether they might play a role in tumor cell dormancy. In addition, we comment whether extracellular vesicle-mediated signals may be involved in tumor cell awakening, considering the possibility that extracellular vesicles might serve as biomarkers to detect early metastasis and/or minimal residual disease (MRD) monitoring.

Use of extracellular vesicles from lymphatic drainage as surrogate markers of melanoma progression and BRAF V600E mutation

García-Silva et al. show for the first time that extracellular vesicles isolated from the exudative seroma obtained from the lymphatic drainage implanted in melanoma patients after lymphadenectomy can be interrogated for melanoma markers and BRAF mutations. Profiling the BRAF^V600E mutation in this biofluid is a novel approach to predict disease relapse.

Liquid biopsies from cancer patients have the potential to improve diagnosis and prognosis. The assessment of surrogate markers of tumor progression in circulating extracellular vesicles could be a powerful non-invasive approach in this setting. We have characterized extracellular vesicles purified from the lymphatic drainage also known as exudative seroma (ES) of stage III melanoma patients obtained after lymphadenectomy. Proteomic analysis showed that seroma-derived exosomes are enriched in proteins resembling melanoma progression. In addition, we found that the BRAF^V600E mutation can be detected in ES-derived extracellular vesicles and its detection correlated with patients at risk of relapse.