Lymph Vessels Associate with Cancer Stem Cells from Initiation to Malignant Stages of Squamous Cell Carcinoma.

Tumor-associated lymph vessels and lymph node involvement are critical staging criteria in several cancers. In skin squamous cell carcinoma, lymph vessels play a role in cancer development and metastatic spread. However, their relationship with the cancer stem cell niche at early tumor stages remains unclear. To address this gap, we studied the lymph vessel localization at the cancer stem cell niche and observed an association from benign skin lesions to malignant stages of skin squamous cell carcinoma. By co-culturing lymphatic endothelial cells with cancer cell lines representing the initiation and promotion stages, and conducting RNA profiling, we observed a reciprocal induction of cell adhesion, immunity regulation, and vessel remodeling genes, suggesting dynamic interactions between lymphatic and cancer cells. Additionally, imaging analyses of the cultured cells revealed the establishment of heterotypic contacts between cancer cells and lymph endothelial cells, potentially contributing to the observed distribution and maintenance at the cancer stem cell niche, inducing downstream cellular responses. Our data provide evidence for an association of lymph vessels from the early stages of skin squamous cell carcinoma development, opening new avenues for better comprehending their involvement in cancer progression.

Hematopoietic Stem Cell (HSC)-Independent Progenitors Are Susceptible to Mll-Af9-Induced Leukemic Transformation.

Infant acute myeloid leukemia (AML) is a heterogeneous disease, genetically distinct from its adult counterpart. Chromosomal translocations involving the KMT2A gene (MLL) are especially common in affected infants of less than 1 year of age, and are associated with a dismal prognosis. While these rearrangements are likely to arise in utero, the cell of origin has not been conclusively identified. This knowledge could lead to a better understanding of the biology of the disease and support the identification of new therapeutic vulnerabilities. Over the last few years, important progress in understanding the dynamics of fetal hematopoiesis has been made. Several reports have highlighted how hematopoietic stem cells (HSC) provide little contribution to fetal hematopoiesis, which is instead largely sustained by HSC-independent progenitors. Here, we used conditional Cre-Lox transgenic mouse models to engineer the Mll-Af9 translocation in defined subsets of embryonic hematopoietic progenitors. We show that embryonic hematopoiesis is generally permissive for Mll-Af9-induced leukemic transformation. Surprisingly, the selective introduction of Mll-Af9 in HSC-independent progenitors generated a transplantable myeloid leukemia, whereas it did not when introduced in embryonic HSC-derived cells. Ex vivo engineering of the Mll-Af9 rearrangement in HSC-independent progenitors using a CRISPR/Cas9-based approach resulted in the activation of an aberrant myeloid-biased self-renewal program. Overall, our results demonstrate that HSC-independent hematopoietic progenitors represent a permissive environment for Mll-Af9-induced leukemic transformation, and can likely act as cells of origin of infant AML.

Human SLFN5 and its Xenopus Laevis ortholog regulate entry into mitosis and oocyte meiotic resumption.

The Schlafen gene family was first described in mice as a regulator of thymocyte development. Further studies showed involvement of human orthologs in different processes related with viral replication, cellular proliferation, and differentiation. In recent years, a new role for human Slfn11 in DNA replication and chromatin remodeling was described. As commonly observed in many gene families, Slfn paralogs show a tissue-specific expression. This made it difficult to reach conclusions which can be valid in different biological models regarding the function of the different Schlafen proteins. In the present study, we investigate the involvement of SLFN5 in cell-cycle regulation and cell proliferation. A careful analysis of SLFN5 expression revealed that SLFN5 is highly expressed in proliferating tissues and that the protein is ubiquitously present in all the tissues and cell line models we analyzed. Very interestingly, SLFN5 expression oscillates during cell cycle, peaking during S phase. The fact that SLFN5 interacts with protein phosphatase 2A and that SLFN5 depletion causes cell cycle arrest and cellular apoptosis, suggests a direct involvement of this human paralog in cell cycle progression and cellular proliferation. We substantiated our in vitro and in cellulo results using Xenopus laevis oocytes to show that mRNA depletion of the unique Slfn gene present in Xenopus, whose protein sequence shares 80% of homology with SLFN5, recapitulates the phenotype observed in human cells preventing the resumption of meiosis during oocyte development.

Prenatal Origin of Pediatric Leukemia: Lessons From Hematopoietic Development.

Several lines of evidence suggest that childhood leukemia, the most common cancer in young age, originates during in utero development. However, our knowledge of the cellular origin of this large and heterogeneous group of malignancies is still incomplete. The identification and characterization of their cell of origin is of crucial importance in order to define the processes that initiate and sustain disease progression, to refine faithful animal models and to identify novel therapeutic approaches. During embryogenesis, hematopoiesis takes place at different anatomical sites in sequential waves, and occurs in both a hematopoietic stem cell (HSC)-dependent and a HSC-independent fashion. Despite the recently described relevance and complexity of HSC-independent hematopoiesis, few studies have so far investigated its potential involvement in leukemogenesis. Here, we review the current knowledge on prenatal origin of leukemias in the context of recent insights in developmental hematopoiesis.

TP53 deficiency permits chromosome abnormalities and karyotype heterogeneity in acute myeloid leukemia.

Abnormal karyotypes are common in cancer cells and frequently observed in acute myeloid leukemia (AML), in which complex karyotype aberrations are associated with poor prognosis. How exactly abnormal karyotypes arise and are propagated in AML is unclear. TP53 mutations and deletions are frequent in complex karyotype AML, suggesting a role of TP53 alterations in the development of chromosome abnormalities. Here, we generated isogenic TP53-knockout versions of the euploid AML cell line EEB to investigate the impact of TP53 on karyotype stability. We show that chromosome abnormalities spontaneously arise in TP53-deficient cells. Numerical aneuploidy could, to some extent, be propagated in a TP53-proficient setting, indicating that it does not necessarily trigger TP53 activation. In contrast, tolerance to structural chromosome aberrations was almost entirely restricted to TP53-knockout clones, all of which were able to continue proliferation in the presence of damaged DNA. Mechanistically, as a source of chromosome aberrations, limited numerical but not structural chromosomal instability was tolerated by TP53-wildtype cells. In contrast, structural instability was found only in TP53-knockout cells. Together, in myeloid cells TP53 loss allows for the development of complex karyotype aberrations and karyotype heterogeneity by perpetuation of chromosome segregation errors.

Asymmetric Centriole Numbers at Spindle Poles Cause Chromosome Missegregation in Cancer.

Chromosomal instability is a hallmark of cancer and correlates with the presence of extra centrosomes, which originate from centriole overduplication. Overduplicated centrioles lead to the formation of centriole rosettes, which mature into supernumerary centrosomes in the subsequent cell cycle. While extra centrosomes promote chromosome missegregation by clustering into pseudo-bipolar spindles, the contribution of centriole rosettes to chromosome missegregation is unknown. We used multi-modal imaging of cells with conditional centriole overduplication to show that mitotic rosettes in bipolar spindles frequently harbor unequal centriole numbers, leading to biased chromosome capture that favors binding to the prominent pole. This results in chromosome missegregation and aneuploidy. Rosette mitoses lead to viable offspring and significantly contribute to progeny production. We further show that centrosome abnormalities in primary human malignancies frequently consist of centriole rosettes. As asymmetric centriole rosettes generate mitotic errors that can be propagated, rosette mitoses are sufficient to cause chromosome missegregation in cancer.