Unbalancing cAMP and Ras/MAPK pathways as a therapeutic strategy for cutaneous neurofibromas

Cutaneous neurofibromas (cNFs) are benign Schwann cell (SC) tumors arising from subepidermal glia. Individuals with neurofibromatosis type 1 (NF1) may develop thousands of cNFs, which greatly affect their quality of life. cNF growth is driven by the proliferation of NF1-/- SCs and their interaction with the NF1+/- microenvironment. We analyzed the crosstalk between human cNF-derived SCs and fibroblasts (FBs), identifying an expression signature specific to the SC-FB interaction. We validated the secretion of proteins involved in immune cell migration, suggesting a role of SC-FB crosstalk in immune cell recruitment. The signature also captured components of developmental signaling pathways, including the cAMP elevator G protein-coupled receptor 68 (GPR68). Activation of Gpr68 by ogerin in combination with the MEK inhibitor (MEKi) selumetinib reduced viability and induced differentiation and death of human cNF-derived primary SCs, a result corroborated using an induced pluripotent stem cell-derived 3D neurofibromasphere model. Similar results were obtained using other Gpr68 activators or cAMP analogs/adenylyl cyclase activators in combination with selumetinib. Interestingly, whereas primary SC cultures restarted their proliferation after treatment with selumetinib alone was stopped, the combination of ogerin-selumetinib elicited a permanent halt on SC expansion that persisted after drug removal. These results indicate that unbalancing the Ras and cAMP pathways by combining MEKi and cAMP elevators could be used as a potential treatment for cNFs.

Generation of human iPSC-derived neurofibromaspheres for in vitro and in vivo uses

Neurofibromas are benign peripheral nervous system tumors associated with neurofibromatosis type 1, which originate from NF1(-/-) Schwann cell precursors. We describe a protocol to generate neurofibromaspheres by differentiating NF1(-/-) Schwann cells from induced pluripotent stem cells and combining them with neurofibroma primary fibroblasts. We also describe the development of neurofibroma-like tumors when neurofibromaspheres are engrafted in the sciatic nerve of nude mice. This model constitutes a versatile platform for drug screening and the study of neurofibroma biology. For complete details on the use and execution of this protocol, please refer to Mazuelas et al. (2022).¹.

Deep genomic analysis of malignant peripheral nerve sheath tumor cell lines challenges current malignant peripheral nerve sheath tumor diagnosis

Malignant peripheral nerve sheath tumors (MPNSTs) are soft-tissue sarcomas of the peripheral nervous system that develop either sporadically or in the context of neurofibromatosis type 1 (NF1). MPNST diagnosis can be challenging and treatment outcomes are poor. We present here a resource consisting of the genomic characterization of 9 widely used human MPNST cell lines for their use in translational research. NF1-related cell lines recapitulated primary MPNST copy number profiles, exhibited NF1, CDKN2A, and SUZ12/EED tumor suppressor gene (TSG) inactivation, and presented no gain-of-function mutations. In contrast, sporadic cell lines collectively displayed different TSG inactivation patterns and presented kinase-activating mutations, fusion genes, altered mutational frequencies and COSMIC signatures, and different methylome-based classifications. Cell lines re-classified as melanomas and other sarcomas exhibited a different drug-treatment response. Deep genomic analysis, methylome-based classification, and cell-identity marker expression, challenged the identity of common MPNST cell lines, opening an opportunity to revise MPNST differential diagnosis.

Chromosomal translocations inactivating CDKN2A support a single path for malignant peripheral nerve sheath tumor initiation

Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas with poor prognosis, developing either sporadically or in persons with neurofibromatosis type 1 (NF1). Loss of CDKN2A/B is an important early event in MPNST progression. However, many reported MPNSTs exhibit partial or no inactivation of CDKN2A/B, raising the question of whether there is more than one molecular path for MPNST initiation. We present here a comprehensive genomic analysis of MPNST cell lines and tumors to explore in depth the status of CDKN2A. After accounting for CDKN2A deletions and point mutations, we uncovered a previously unnoticed high frequency of chromosomal translocations involving CDKN2A in both MPNST cell lines and primary tumors. Most identified translocation breakpoints were validated by PCR amplification and Sanger sequencing. Many breakpoints clustered in an intronic 500 bp hotspot region adjacent to CDKN2A exon 2. We demonstrate the bi-allelic inactivation of CDKN2A in all tumors (n = 15) and cell lines (n = 8) analyzed, supporting a single molecular path for MPNST initiation in both sporadic and NF1-related MPNSTs. This general CDKN2A inactivation in MPNSTs has implications for MPNST diagnostics and treatment. Our findings might be relevant for other tumor types with high frequencies of CDKN2A inactivation.

The IL-2RG R328X nonsense mutation allows partial STAT-5 phosphorylation and defines a critical region involved in the leaky-SCID phenotype

In addition to their detection in typical X-linked severe combined immunodeficiency, hypomorphic mutations in the interleukin (IL)-2 receptor common gamma chain gene (IL2RG) have been described in patients with atypical clinical and immunological phenotypes. In this leaky clinical phenotype the diagnosis is often delayed, limiting prompt therapy in these patients. Here, we report the biochemical and functional characterization of a nonsense mutation in exon 8 (p.R328X) of IL2RG in two siblings: a 4-year-old boy with lethal Epstein-Barr virus-related lymphoma and his asymptomatic 8-month-old brother with a T^low B⁺ natural killer (NK)⁺ immunophenotype, dysgammaglobulinemia, abnormal lymphocyte proliferation and reduced levels of T cell receptor excision circles. After confirming normal IL-2RG expression (CD132) on T lymphocytes, signal transducer and activator of transcription-1 (STAT-5) phosphorylation was examined to evaluate the functionality of the common gamma chain (γ_c ), which showed partially preserved function. Co-immunoprecipitation experiments were performed to assess the interaction capacity of the R328X mutant with Janus kinase (JAK)3, concluding that R328X impairs JAK3 binding to γ_c . Here, we describe how the R328X mutation in IL-2RG may allow partial phosphorylation of STAT-5 through a JAK3-independent pathway. We identified a region of three amino acids in the γ_c intracellular domain that may be critical for receptor stabilization and allow this alternative signaling. Identification of the functional consequences of pathogenic IL2RG variants at the cellular level is important to enable clearer understanding of partial defects leading to leaky phenotypes.