Regulation of large-scale chromatin unfolding by Smad4

Regulation of TGFβ Signalling by TRPV4 in Chondrocytes

The growth factor TGFβ and the mechanosensitive calcium-permeable cation channel TRPV4 are both important for the development and maintenance of many tissues. Although TRPV4 and TGFβ both affect core cellular functions, how their signals are integrated is unknown. Here we show that pharmacological activation of TRPV4 significantly increased the canonical response to TGFβ stimulation in chondrocytes. Critically, this increase was only observed when TRPV4 was activated after, but not before TGFβ stimulation. The increase was prevented by pharmacological TRPV4 inhibition or knockdown and is calcium/CamKII dependent. RNA-seq analysis after TRPV4 activation showed enrichment for the TGFβ signalling pathway and identified JUN and SP1 as key transcription factors involved in this response. TRPV4 modulation of TGFβ signalling represents an important pathway linking mechanical signalling to tissue development and homeostasis.

LINE-1 ORF-1p functions as a novel HGF/ETS-1 signaling pathway co-activator and promotes the growth of MDA-MB-231 cell

Long interspersed nucleotide element (LINE)-1 ORF-1p is encoded by the human pro-oncogene LINE-1. It is involved in the development and progression of several human carcinomas, such as hepatocellular carcinoma and lung and breast cancers. The hepatocyte growth factor (HGF)/ETS-1 signaling pathway is involved in regulation of cancer cell proliferation, metastasis and invasion. The biological function of the interaction between LINE-1 ORF-1p and the HGF/ETS-1 signaling pathway in regulation of human breast cancer proliferation remains largely unknown. Here, we showed that LINE-1 ORF-1p enhanced ETS-1 transcriptional activity and increased expression of downstream genes of ETS-1. Interaction between ETS-1 and LINE-1 ORF-1p was identified by immunoprecipitation assays. LINE-1 ORF-1p modulated ETS-1 activity through cytoplasm/nucleus translocation and recruitment to the ETS-1 binding element in the MMP1 gene promoter. We also showed that LINE-1 ORF-1p promoted proliferation and anchorage-independent growth of MDA-MB-231 breast cancer cells. By investigating a novel role of the LINE-1 ORF-1p in the HGF/ETS-1 signaling pathway and MDA-MB-231 cells, we demonstrated that LINE-1 ORF-1p may be a novel ETS-1 coactivator and molecular target for therapy of human triple negative breast cancer.

Long interspersed nuclear element ORF-1 protein promotes proliferation and resistance to chemotherapy in hepatocellular carcinoma

AIM: To clarify the specific roles and mechanisms of long interspersed nuclear element-1 ORF-1 protein [human long interspersed nuclear element-1 (LINE-1), ORF-1p] in chemotherapeutic drug resistance and cell proliferation regulation in hepatocellular carcinoma (HCC) cells.

METHODS: MTT assays were performed to identify the effect of the chemotherapeutic drug toxicity on HepG2 cells. Cell proliferation inhibition and the IC₅₀ were calculated by the Origin 8.0 software. Western blotting assays were performed to investigate whether LINE-1 ORF-1p modulates the expression of some important genes, including p53, p27, p15, Bcl-2, mdr, and p-gp. To corroborate the proliferation and anchor-independent growth results, the HepG2 cells were analyzed by flow cytometry to investigate the effect of LINE-1 ORF-1p on the apoptosis regulation.

RESULTS: LINE-1 ORF-1p contributed to the resistance to several chemotherapeutic drugs (cisplatin and epirubicin) in HepG2 cells. The IC₅₀ of the epirubicin and cisplatin increased from 36.04 nmol/L to 59.11 nmol/L or from 37.94 nmol/L to 119.32 nmol/L. Repression of LINE-1 ORF-1p expression by the siRNA could markedly enhance the response of HepG2 cells to the epirubicin and cisplatin. The IC₅₀ correspondingly decreased from 28.06 nmol/L to 3.83 nmol/L or from 32.04 nmol/L to 2.89 nmol/L. Interestingly, down-regulation of LINE-1 ORF-1p level by siRNA could promote the response of HepG2 cells to the paclitaxel. The IC₅₀ decreased from 35.90 nmol/L to 7.36 nmol/L. However, overexpression of LINE-1 ORF-1p did not modulate the paclitaxel toxicity in HepG2 cells. Further Western blotting revealed that LINE-1 ORF-1p enhanced mdr and p-gp gene expression. As a protein arrested in the nucleus, LINE-1 ORF-1p may function through modulating transcriptional activity of some important transcription factors. Indeed, LINE-1 ORF-1p promoted HepG2 cell proliferation, anchor-independent growth and protected the cells against apoptosis through modulating the expression of p15, p21, p53, and Bcl-2 genes.

CONCLUSION: LINE-1 ORF-1p promotes HepG2 cell proliferation and plays an important role in the resistance of chemotherapeutic drugs. By establishing novel roles and defining the mechanisms of LINE-1 ORF-1p in HCC chemotherapeutic drug resistance and cell proliferation regulation, this study indicates that LINE-1 ORF-1p is a potential target for overcoming HCC chemotherapeutic resistance.

Cellular reprogramming for the creation of patient-specific embryonic stem cells

The success of somatic cell nuclear transfer in mammals has opened the possibility to dedifferentiate cells from a patient into embryonic stem cells and in doing so, potentially generate all different cells and tissues of the human body. These cells could be later transplanted to the same patient without immune rejection. Whereas this principle has been demonstrated in laboratory animals, it is yet to be shown to work in primates. Herein we discuss the probability of somatic cell nuclear transfer becoming a real therapeutic alternative as well as the potential emerging dedifferentiation approaches that may eventually replace it.

Potentiation of Smad-mediated transcriptional activation by the RNA-binding protein RBPMS

Smad2, Smad3 and Smad4 proteins are considered to be key mediators of transforming growth factor-beta (TGF-beta) signaling. However, the identities of the Smad partners mediating TGF-beta signaling are not fully understood. Here, we show that RNA-binding protein with multiple splicing (RBPMS), a member of the RNA-binding protein family, physically interacts with Smad2, Smad3 and Smad4 both in vitro and in vivo. The presence of TGF-beta increases the binding of RBPMS with these Smad proteins. Consistent with the binding results, overexpression of RBPMS enhances Smad-dependent transcriptional activity in a TGF-beta-dependent manner, whereas knockdown of RBPMS decreases this activity. RBPMS interacts with TGF-beta receptor type I (TbetaR-I), increases phosphorylation of C-terminal SSXS regions in Smad2 and Smad3, and promotes the nuclear accumulation of the Smad proteins. Moreover, RBPMS fails to enhance the transcriptional activity of Smad2 and Smad3 that lack the C-terminal phosphorylation sites. Our data provide the first evidence for an RNA-binding protein playing a role in regulation of Smad-mediated transcriptional activity and suggest that RBPMS stimulates Smad-mediated transactivation possibly through enhanced phosphorylation of Smad2 and Smad3 at the C-terminus and promotion of the nuclear accumulation of the Smad proteins.

Transcription of gonadotropin beta subunit genes involves cross-talk between the transcription factors and co-regulators that mediate actions of the regulatory hormones

The gonadotropins LH and FSH have distinct temporal patterns of expression as a result of differential regulation by hormones such as GnRH, steroids and activin. This specific regulation is due to diverse sets of transcription factors that are recruited to the promoters of these genes, and recruit specific co-activator complexes which function to stabilize interactions with the general transcription factors and RNA polymerase II, and also to induce covalent modifications of the histone tails at these gene loci. As these molecular mechanisms are elucidated, the nature of nuclear cross-talk between the various hormonally induced pathways is becoming evident, revealing both negative and positive effects of interacting transcription factors and co-regulators. This paper will review current knowledge on the transcriptional regulation of gonadotropin beta subunit gene expression in the chromatin setting, and will present new data pertaining to nuclear cross-talk between the various endocrine-induced pathways regulating gonadotropin gene transcription.

Smads and chromatin modulation

Smad proteins are critical intracellular effector proteins and regulators of transforming growth factor type beta (TGFbeta) modulated gene transcription. They directly convey signals that initiate at ligand-bound receptor complexes and end in the nucleus with changes in programs of gene expression. Activated Smad proteins seem to recruit chromatin modifying proteins to target genes besides cooperating with DNA-bound transcription factors. We survey here the current and still emerging knowledge on Smad-binding factors, and their different mechanisms of chromatin modification in particular, in Smad-dependent TGFbeta signaling.

Human pescadillo induces large-scale chromatin unfolding

The human pescadillo gene encodes a protein with a BRCT domain. Pescadillo plays an important role in DNA synthesis, cell proliferation and transformation. Since BRCT domains have been shown to induce chromatin large-scale unfolding, we tested the role of Pescadillo in regulation of large-scale chromatin unfolding. To this end, we isolated the coding region of Pescadillo from human mammary MCF10A cells. Compared with the reported sequence, the isolated Pescadillo contains in-frame deletion from amino acid 580 to 582. Targeting the Pescadillo to an amplified, lac operator-containing chromosome region in the mammalian genome results in large-scale chromatin decondensation. This unfolding activity maps to the BRCT domain of Pescadillo. These data provide a new clue to understanding the vital role of Pescadillo.

XBP-1 increases ERalpha transcriptional activity through regulation of large-scale chromatin unfolding

Human X box binding protein 1 (XBP-1) is a transcription factor essential for hepatocyte growth, the differentiation of plasma cells, and the unfolded protein response. Recently, we have demonstrated that two forms of XBP-1, XBP-1S, and XBP-1U, enhance estrogen receptor alpha (ERalpha)-dependent transcriptional activity in a ligand-independent manner. However, how XBP-1S and XBP-1U regulate ERalpha transcriptional activity remains unknown. Here, we report that XBP-1S and XBP-1U induce large-scale chromatin unfolding by targeting the XBP-1 proteins to an amplified, lac operator-containing chromosome region in mammalian cells. This unfolding activity maps to the transactivation domains of XBP-1S and XBP-1U. Wild-type XBP-1S and XBP-1U, but not the mutants that completely abolished the ERalpha transcriptional activation, increased the chromatin unfolding activity of ERalpha. These data identify a novel function of XBP-1 and suggest that regulation of large-scale chromatin unfolding by XBP-1 may be responsible for the enhancement of ERalpha transcriptional activity.