Role of Lamin A/C as Candidate Biomarker of Aggressiveness and Tumorigenicity in Glioblastoma Multiforme.

Nuclear lamina components have long been regarded as scaffolding proteins, forming a dense fibrillar structure necessary for the maintenance of the nucleus shape in all the animal kingdom. More recently, mutations, aberrant localisation and deregulation of these proteins have been linked to several diseases, including cancer. Using publicly available data we found that the increased expression levels of the nuclear protein Lamin A/C correlate with a reduced overall survival in The Cancer Genome Atlas Research Network (TCGA) patients affected by glioblastoma multiforme (GBM). We show that the expression of the LMNA gene is linked to the enrichment of cancer-related pathways, particularly pathways related to cell adhesion and cell migration. Mimicking the modulation of LMNA in a GBM preclinical cancer model, we confirmed both in vitro and in vivo that the increased expression of LMNA is associated with an increased aggressiveness and tumorigenicity. In addition, delving into the possible mechanism behind LMNA-induced GBM aggressiveness and tumorigenicity, we found that the mTORC2 component, Rictor, plays a central role in mediating these effects.

Circulating miRNAs in Small Extracellular Vesicles Secreted by a Human Melanoma Xenograft in Mouse Brains.

The identification of liquid biomarkers remains a major challenge to improve the diagnosis of melanoma patients with brain metastases. Circulating miRNAs packaged into tumor-secreted small extracellular vesicles (sEVs) contribute to tumor progression. To investigate the release of tumor-secreted miRNAs by brain metastasis, we developed a xenograft model where human metastatic melanoma cells were injected intracranially in nude mice. The comprehensive profiles of both free miRNAs and those packaged in sEVs secreted by the melanoma cells in the plasma demonstrated that most (80%) of the sEV-associated miRNAs were also present in serum EVs from a cohort of metastatic melanomas, included in a publicly available dataset. Remarkably, among them, we found three miRNAs (miR-224-5p, miR-130a-3p and miR-21-5p) in sEVs showing a trend of upregulation during melanoma progression. Our model is proven to be valuable for identifying miRNAs in EVs that are unequivocally secreted by melanoma cells in the brain and could be associated to disease progression.

Lamin A/C Is Required for ChAT-Dependent Neuroblastoma Differentiation.

The mouse neuroblastoma N18TG2 clone is unable to differentiate and is defective for the enzymes of the biosynthesis of neurotransmitters. The forced expression of choline acetyltransferase (ChAT) in these cells results in the synthesis and release of acetylcholine (Ach) and hence in the expression of neurospecific features and markers. To understand how the expression of ChAT triggered neuronal differentiation, we studied the differences in genome-wide transcription profiles between the N18TG2 parental cells and its ChAT-expressing 2/4 derived clone. The engagement of the 2/4 cells in the neuronal developmental program was confirmed by the increase of the expression level of several differentiation-related genes and by the reduction of the amount of transcripts of cell cycle genes. At the same time, we observed a massive reorganization of cytoskeletal proteins in terms of gene expression, with the accumulation of the nucleoskeletal lamina component Lamin A/C in differentiating cells. The increase of the Lmna transcripts induced by ChAT expression in 2/4 cells was mimicked treating the parental N18TG2 cells with the acetylcholine receptor agonist carbachol, thus demonstrating the direct role played by this receptor in neuron nuclei maturation. Conversely, a treatment of 2/4 cells with the muscarinic receptor antagonist atropine resulted in the reduction of the amount of Lmna RNA. Finally, the hypothesis that Lmna gene product might play a crucial role in the ChAT-dependent molecular differentiation cascade was strongly supported by Lmna knockdown in 2/4 cells leading to the downregulation of genes involved in differentiation and cytoskeleton formation and to the upregulation of genes known to regulate self-renewal and stemness.

Down-regulation of the Lamin A/C in neuroblastoma triggers the expansion of tumor initiating cells.

Tumor-initiating cells constitute a population within a tumor mass that shares properties with normal stem cells and is considered responsible for therapy failure in many cancers. We have previously demonstrated that knockdown of the nuclear envelope component Lamin A/C in human neuroblastoma cells inhibits retinoic acid-mediated differentiation and results in a more aggressive phenotype. In addition, Lamin A/C is often lost in advanced tumors and changes in the nuclear envelope composition occur during tumor progression. Based on our previous data and considering that Lamin A/C is expressed in differentiated tissues, we hypothesize that the lack of Lamin A/C could predispose cells toward a stem-like phenotype, thus influencing the development of tumor-initiating cells in neuroblastoma. This paper demonstrates that knockdown of Lamin A/C triggers the development of a tumor-initiating cell population with self-renewing features in human neuroblastoma cells. We also demonstrates that the development of TICs is due to an increased expression of MYCN gene and that in neuroblastoma exists an inverse relationship between LMNA and MYCN expression.