Tumorigenic effects of TLX overexpression in HEK 293T cells

The human orphan receptor TLX (NR2E1) is a key regulator of neurogenesis, adult stem cell maintenance, and tumorigenesis. However, little is known about the genetic and transcriptomic events that occur following TLX overexpression in human cell lines.

Here, we used cytogenetics and RNA sequencing to investigate the effect of TLX overexpression with an inducible vector system in the HEK 293T cell line.

Conventional spectral karyotyping was used to identify chromosomal abnormalities, followed by fluorescence in situ hybridization (FISH) analysis on chromosome spreads to assess TLX DNA copy number. Illumina paired-end whole transcriptome sequencing was then performed to characterize recurrent genetic variants (single nucleotide polymorphisms (SNPs) and indels), expressed gene fusions, and gene expression profiles. Lastly, flow cytometry was used to analyze cell cycle distribution. Intriguingly, we show that upon transfection with a vector containing the human TLX gene (eGFP-hTLX), an isochromosome forms on the long arm of chromosome 6, thereby resulting in DNA gain of the TLX locus (6q21) and upregulation of TLX. Induction of the eGFP-hTLX vector further increased TLX expression levels, leading to G0-G1 cell cycle arrest, genetic aberrations, modulation of gene expression patterns, and crosstalk with other nuclear receptors (AR, ESR1, ESR2, NR1H4, and NR3C2). We identified a 49-gene signature associated with central nervous system (CNS) development and carcinogenesis, in addition to potentially cancer-driving gene fusions (LARP1-CNOT8 and NSL1-ZDBF2) and deleterious genetic variants (frameshift insertions in the CTSH, DBF4, POSTN, and WDR78 genes).

Taken together, these findings illustrate that TLX may play a pivotal role in tumorigenesis via genomic instability and perturbation of cancer-related processes.