Induction of epithelial-mesenchymal transition in thyroid follicular cells is associated with cell adhesion alterations and low-dose hyper-radiosensitivity

BACKGROUND

Epithelial-mesenchymal transition (EMT) is associated with altered cellular adhesion. We previously demonstrated that cellular adhesion influences Low-dose Hyper-Radiosensitivity (HRS) in a variety of tumor cells. However, the relationship of low-dose HRS with the phenotypic plasticity incurred by EMT during the neoplastic transformation remains to be elucidated.

OBJECTIVE

To investigate whether acquisition of EMT phenotype during progressive neoplastic transformation may affect low-dose radiation sensitivity.

METHODS

Primary thyroid cells obtained from a human cystic thyroid nodule were first subjected to nutritional stress. This yielded immortalized INM-Thy1 cell strain, which was further treated with either multiple γ-radiation fractions (1.5 Gy each) or repetitive cycles of 3-methylcholanthrene and phorbol-12-myristate-13-acetate, yielding two progressive transformants, viz., INM-Thy1R and INM-Thy1C. Morphological alterations, chromosomal double-minutes, cell adhesion proteins, anchorage dependency, tumorigenicity in nude mice and cellular radiosensitivity were studied in these strains.

RESULTS

Both transformants (INM-Thy1R, INM-Thy1C) displayed progressive tumorigenic features, viz., soft agar colony growth and solid tumor growth in nude mice, coupled with features of epithelial-mesenchymal transition and activated Wnt pathway. Incidentally, the chemical-induced transformant (INM-Thy1C) displayed a prominent HRS (αs/αr = 29.35) which remained unaffected at high cell density. However, the parental (INM-Thy1) cell line as well as radiation-induced transformant (INM-Thy1R) failed to show this hypersensitivity.

CONCLUSION

The study shows that induction of EMT in thyroid follicular cells may accompany increased susceptibility to low-dose ionizing radiation, which was attenuated by adaptive resistance acquired during radiation-induced transformation.

miRNA dysregulation is an emerging modulator of genomic instability

Genomic instability consists of a range of genetic alterations within the genome that contributes to tumor heterogeneity and drug resistance. It is a well-established characteristic of most cancer cells. Genome instability induction results from defects in DNA damage surveillance mechanisms, mitotic checkpoints and DNA repair machinery. Accumulation of genetic alterations ultimately sets cells towards malignant transformation. Recent studies suggest that miRNAs are key players in mediating genome instability. miRNAs are a class of small RNAs expressed in most somatic tissues and are part of the epigenome. Importantly, in many cancers, miRNA expression is dysregulated. Consequently, this review examines the role of miRNA dysregulation as a causal step for induction of genome instability and subsequent carcinogenesis. We focus specifically on mechanistic studies assessing miRNA(s) and specific subtypes of genome instability or known modes of genome instability. In addition, we provide insight on the existing knowledge gaps within the field and possible ways to address them.

Mutant GTF2I induces cell transformation and metabolic alterations in thymic epithelial cells

The pathogenesis of thymic epithelial tumors (TETs) is poorly understood. Recently we reported the frequent occurrence of a missense mutation in the GTF2I gene in TETs and hypothesized that GTF2I mutation might contribute to thymic tumorigenesis. Expression of mutant TFII-I altered the transcriptome of normal thymic epithelial cells and upregulated several oncogenic genes. Gtf2i L424H knockin cells exhibited cell transformation, aneuploidy, and increase tumor growth and survival under glucose deprivation or DNA damage. Gtf2i mutation also increased the expression of several glycolytic enzymes, cyclooxygenase-2, and caused modifications of lipid metabolism. Elevated cyclooxygenase-2 expression by Gtf2i mutation was required for survival under metabolic stress and cellular transformation of thymic epithelial cells. Our findings identify GTF2I mutation as a new oncogenic driver that is responsible for transformation of thymic epithelial cells.

Critical role of miR-10b in B-RafV600E dependent anchorage independent growth and invasion of melanoma cells

Recent high-throughput-sequencing of cancer genomes has identified oncogenic mutations in the B-Raf genetic locus as one of the critical events in melanomagenesis. B-Raf encodes a serine/threonine kinase that regulates the MAPK/ERK kinase (MEK) and extracellular signal-regulated kinase (ERK) protein kinase cascade. In normal cells, the activity of B-Raf is tightly regulated and is required for cell growth and survival. B-Raf gain-of-function mutations in melanoma frequently lead to unrestrained growth, enhanced cell invasion and increased viability of cancer cells. Although it is clear that the invasive phenotypes of B-Raf mutated melanoma cells are stringently dependent on B-Raf-MEK-ERK activation, the downstream effector targets that are required for oncogenic B-Raf-mediated melanomagenesis are not well defined. miRNAs have regulatory functions towards the expression of genes that are important in carcinogenesis. We observed that miR-10b expression correlates with the presence of the oncogenic B-Raf (B-RafV600E) mutation in melanoma cells. While expression of miR-10b enhances anchorage-independent growth of B-Raf wild-type melanoma cells, miR-10b silencing decreases B-RafV600E cancer cell invasion in vitro. Importantly, the expression of miR-10b is required for B-RafV600E-mediated anchorage independent growth and invasion of melanoma cells in vitro. Taken together our results suggest that miR-10b is an important mediator of oncogenic B-RafV600E activity in melanoma.

Two-pore channel 1 interacts with citron kinase, regulating completion of cytokinesis

Two-pore channels (TPC1, 2, and 3) are recently identified endolysosmal ion channels, but remain poorly characterized. In this study, we show for the first time a role for TPC1 in cytokinesis, the final step in cell division. HEK 293 T-REx cells inducibly overexpressing TPC1 demonstrated a lack of proliferation accompanied by multinucleation and an increase in G2/M cycling cells. Increased TPC1 was associated with a concomitant accumulation of active RhoGTP and a decrease in phosphorylated myosin light chain (MLC). Finally, we demonstrated a novel interaction between TPC1 and citron kinase (CIT). These results identify TPC1 as a central component of cytokinetic control, specifically during abscission, and introduce a means by which the endolysosomal system may play an active role in this process.