Lineage-restricted sympathoadrenal progenitors confer neuroblastoma origin and its tumorigenicity.

Neuroblastoma (NB) is the most common cancer in infants and it accounts for six percent of all pediatric malignancies. There are several hypotheses proposed on the origins of NB. While there is little genetic evidence to support this, the prevailing model is that NB originates from neural crest stem cells (NCSCs). Utilizing in vivo mouse models, we demonstrate that targeting MYCN oncogene to NCSCs causes perinatal lethality. During sympathoadrenal (SA) lineage development, SOX transcriptional factors drive the transition from NCSCs to lineage-specific progenitors, characterized by the sequential activation of Sox9/Sox10/Sox4/Sox11 genes. We find the NCSCs factor SOX10 is not expressed in neuroblasts, but rather restricted to the Schwannian stroma and is associated with a good prognosis. On the other hand, SOX9 expression in NB cells was associated with several key biological processes including migration, invasion and differentiation. Moreover, manipulating SOX9 gene predominantly affects lineage-restricted SA progenitors. Our findings highlight a unique molecular SOX signature associated with NB that is highly reminiscent of SA progenitor transcriptional program during embryonic development, providing novel insights into NB pathobiology. In summary, we provide multiple lines of evidence suggesting that multipotent NCSCs do not contribute to NB initiation and maintenance.

Oncogenic ALK F1174L drives tumorigenesis in cutaneous squamous cell carcinoma.

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer characterized by increased mortality. Here, we show for the first time that anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase of the insulin receptor superfamily, plays a pivotal role in the pathogenesis of cSCC. Our data demonstrate that the overexpression of the constitutively active, mutated ALK, ALK F1174L , is sufficient to initiate the development of cSCC and is 100% penetrant. Moreover, we show that cSCC development upon ALK F1174L overexpression is independent of the cell-of-origin. Molecularly, our data demonstrate that ALK F1174L cooperates with oncogenic Kras G12D and loss of p53, well-established events in the biology of cSCC. This cooperation results in a more aggressive cSCC type associated with a higher grade histological morphology. Finally, we demonstrate that Stat3 is a key downstream effector of ALK F1174L and likely plays a role in ALK F1174L -driven cSCC tumorigenesis. In sum, these findings reveal that ALK can exert its tumorigenic potential via cooperation with multiple pathways crucial in the pathogenesis of cSCC. Finally, we show that human cSCCs contain mutations in the ALK gene. Taken together, our data identify ALK as a new key player in the pathogenesis of cSCC, and this knowledge suggests that oncogenic ALK signaling can be a target for future clinical trials.

Temporal activation of WNT/ß-catenin signaling is sufficient to inhibit SOX10 expression and block melanoma growth.

Despite advances in the systemic treatment of patients with metastatic melanoma using immune checkpoint and tyrosine kinase inhibitors (TKI), the majority of stage IV melanoma patients eventually succumb to the disease. We have previously identified the transcription factor Sox10 as a crucial player in melanoma, yet the underlying molecular mechanisms mediating Sox10-dependent tumorigenesis remain largely uncharacterized. Here, we show that MEK and RAF inhibitors do not suppress levels of SOX10 protein in patient-derived cells in vitro, as well as in melanoma patients in vivo. In a search for pharmacological inhibitors of SOX10, we performed a mass spectrometry-based screen in human melanoma cells. Subsequent analysis revealed that SOX10 directly interacts with ß-catenin, which is a key mediator of canonical Wnt/ß-catenin signaling. We demonstrate that inhibitors of glycogen synthase kinase 3 alpha/beta (GSK3α/ß) efficiently abrogate SOX10 protein in human melanoma cells in vitro and in melanoma mouse models in vivo. The mechanism of action of GSK3-mediated SOX10 suppression is transcription-independent and relies on the presence of a proteasome degradable form of ß-catenin. Taken together, we provide evidence that activation of canonical Wnt signaling has a profound effect on melanoma growth and is able to counteract Sox10-dependent melanoma maintenance both in vitro and in vivo.

Expression of the Neuroblastoma-Associated ALK-F1174L Activating Mutation During Embryogenesis Impairs the Differentiation of Neural Crest Progenitors in Sympathetic Ganglia.

Neuroblastoma (NB) is an embryonal malignancy derived from the abnormal differentiation of the sympathetic nervous system. The Anaplastic Lymphoma Kinase (ALK) gene is frequently altered in NB, through copy number alterations and activating mutations, and represents a predisposition in NB-genesis when mutated. Our previously published data suggested that ALK activating mutations may impair the differentiation potential of neural crest (NC) progenitor cells. Here, we demonstrated that the expression of the endogenous ALK gene starts at E10.5 in the developing sympathetic ganglia (SG). To decipher the impact of deregulated ALK signaling during embryogenesis on the formation and differentiation of sympathetic neuroblasts, Sox10-Cre;LSL-ALK-F1174L embryos were produced to restrict the expression of the human ALK-F1174L transgene to migrating NC cells (NCCs). First, ALK-F1174L mediated an embryonic lethality at mid-gestation and an enlargement of SG with a disorganized architecture in Sox10-Cre;LSL-ALK-F1174L embryos at E10.5 and E11.5. Second, early sympathetic differentiation was severely impaired in Sox10-Cre;LSL-ALK-F1174L embryos. Indeed, their SG displayed a marked increase in the proportion of NCCs and a decrease of sympathetic neuroblasts at both embryonic stages. Third, neuronal and noradrenergic differentiations were blocked in Sox10-Cre;LSL-ALK-F1174L SG, as a reduced proportion of Phox2b+ sympathoblasts expressed ßIII-tubulin and almost none were Tyrosine Hydroxylase (TH) positive. Finally, at E10.5, ALK-F1174L mediated an important increase in the proliferation of Phox2b+ progenitors, affecting the transient cell cycle exit observed in normal SG at this embryonic stage. Altogether, we report for the first time that the expression of the human ALK-F1174L mutation in NCCs during embryonic development profoundly disturbs early sympathetic progenitor differentiation, in addition to increasing their proliferation, both mechanisms being potential crucial events in NB oncogenesis.