TRBP maintains mammalian embryonic neural stem cell properties by acting as a novel transcriptional coactivator of the Notch signaling pathway

TRBP2, a Major Component of the RNAi Machinery, Is Subjected to Cell Cycle-Dependent Regulation in Human Cancer Cells of Diverse Tissue Origin

BACKGROUND

Transactivation Response Element RNA-binding Protein (TRBP2) is a double-stranded RNA-binding protein widely known for its critical contribution to RNA interference (RNAi), a conserved mechanism of gene-expression regulation mediated through small non-coding RNA moieties (ncRNAs). Nevertheless, TRBP2 has also proved to be involved in other molecular pathways and biological processes, such as cell growth, organism development, spermatogenesis, and stress response. Mutations or aberrant expression of TRBP2 have been previously associated with diverse human pathologies, including Alzheimer's disease, cardiomyopathy, and cancer, with TRBP2 playing an essential role(s) in proliferation, invasion, and metastasis of tumor cells.

METHODS

Hence, the present study aims to investigate, via employment of advanced flow cytometry, immunofluorescence, cell transgenesis and bioinformatics technologies, new, still elusive, functions and properties of TRBP2, particularly regarding its cell cycle-specific control during cancer cell division.

RESULTS

We have identified a novel, mitosis-dependent regulation of TRBP2 protein expression, as clearly evidenced by the lack of its immunofluorescence-facilitated detection during mitotic phases, in several human cancer cell lines of different tissue origin. Notably, the obtained TRBP2-downregulation patterns seem to derive from molecular mechanisms that act independently of oncogenic activities (e.g., malignancy grade), metastatic capacities (e.g., low versus high), and mutational signatures (e.g., p53-/- or p53ΔΥ126) of cancer cells.

CONCLUSIONS

Taken together, we herein propose that TRBP2 serves as a novel cell cycle-dependent regulator, likely exerting mitosis-suppression functions, and, thus, its mitosis-specific downregulation can hold strong promise to be exploited for the efficient and successful prognosis, diagnosis, and (radio-/chemo-)therapy of diverse human malignancies, in the clinic.

YAP inhibits HCMV replication by impairing STING-mediated nuclear transport of the viral genome

YES-associated protein (YAP), a critical actor of the mammalian Hippo signaling pathway involved in diverse biological events, has gained increased recognition as a cellular factor regulated by viral infections, but very few studies have investigated their relationship vice versa. In this study, we show that YAP impairs HCMV replication as assessed by viral gene expression analysis and progeny assays, and that this inhibition occurs at the immediate-early stages of the viral life cycle, at the latest. Using YAP mutants lacking key functional domains and shRNA against TEAD, we show that the inhibitory effects of YAP on HCMV replication are nuclear localization- and TEAD cofactor-dependent. Quantitative real-time PCR (qPCR) and subcellular fractionation analyses reveal that YAP does not interfere with the viral entry process but inhibits transport of the HCMV genome into the nucleus. Most importantly, we show that the expression of stimulator of interferon genes (STING), recently identified as an important component for nuclear delivery of the herpesvirus genome, is severely downregulated by YAP at the level of gene transcription. The functional importance of STING is further confirmed by the observation that STING expression restores YAP-attenuated nuclear transport of the HCMV genome, viral gene expression, and progeny virus production. We also show that HCMV-upregulated YAP reduces expression of STING. Taken together, these findings indicate that YAP possesses both direct and indirect regulatory roles in HCMV replication at different infection stages.

Non-cell autonomous promotion of astrogenesis at late embryonic stages by constitutive YAP activation

Although astrocytes have gained increased recognition as an important regulator in normal brain function and pathology, the mechanisms underlying their genesis are not well understood. In this study, we show that constitutive YAP activation by in utero introduction of a non-degradable form of the YAP gene (YAP 5SA) causes productive GFAP⁺ cell generation at late embryonic periods, and this activity is nuclear localization- and TEAD transcription factor-dependent. Moreover, we found that the GFAP⁺ cells were not YAP 5SA-expressing cells themselves but cells in the vicinity in vivo. Conditioned medium prepared from YAP 5SA-expressing cells induced GFAP⁺ cell production in vitro, suggesting that a soluble factor(s) was mediating the astrogenic activity of YAP 5SA. Indeed, YAP 5SA expression greatly increased CNTF and BMP4 transcription in neural progenitor cells, and a neutralizing antibody against CNTF reduced the astrogenic effects of YAP 5SA-conditioned medium. Furthermore, the YAP 5SA-expressing cells were identified as FN1⁺ mesenchymal cells which are responsible for the precocious astrogenesis. These results suggest a novel molecular mechanism by which YAP activation can induce astrogenesis in a non-cell autonomous manner.

Ttyh1 regulates embryonic neural stem cell properties by enhancing the Notch signaling pathway

Despite growing evidence linking Drosophila melanogaster tweety-homologue 1 (Ttyh1) to normal mammalian brain development and cell proliferation, its exact role has not yet been determined. Here, we show that Ttyh1 is required for the maintenance of neural stem cell (NSC) properties as assessed by neurosphere formation and in vivo analyses of cell localization after in utero electroporation. We find that enhanced Ttyh1-dependent stemness of NSCs is caused by enhanced γ-secretase activity resulting in increased levels of Notch intracellular domain (NICD) production and activation of Notch targets. This is a unique function of Ttyh1 among all other Ttyh family members. Molecular analyses revealed that Ttyh1 binds to the regulator of γ-secretase activity Rer1 in the endoplasmic reticulum and thereby destabilizes Rer1 protein levels. This is the key step for Ttyh1-dependent enhancement of γ-secretase activity, as Rer1 overexpression completely abolishes the effects of Ttyh1 on NSC maintenance. Taken together, these findings indicate that Ttyh1 plays an important role during mammalian brain development by positively regulating the Notch signaling pathway through the downregulation of Rer1.

Gray Matter Heterotopia, Mental Retardation, Developmental Delay, Microcephaly, and Facial Dysmorphisms in a Boy with Ring Chromosome 6: A 10-Year Follow-Up and Literature Review

Ring chromosome 6, r(6), is an extremely rare cytogenetic abnormality with clinical heterogeneity which arises typically de novo. The phenotypes of r(6) can be highly variable, ranging from almost normal to severe malformations and neurological defects. Up to now, only 33 cases have been reported in the literature. In this 10-year follow-up study, we report a case presenting distinctive facial features, severe developmental delay, and gray matter heterotopia with r(6) and terminal deletions of 6p25.3 (115426-384174, 268 kb) and 6q26-27 (168697778-170732033, 2.03 Mb) encompassing 2 and 15 candidate genes, respectively, which were detected using G-banding karyotyping, FISH, and chromosomal microarray analysis. We also analyzed the available information on the clinical features of the reported r(6) cases in order to provide more valuable information on genotype-phenotype correlations. To the best of our knowledge, this is the first report of gray matter heterotopia manifested in a patient with r(6) in China, and the deletions of 6p and 6q in our case are the smallest with the precise size of euchromatic material loss currently known.