Nandrolone, an anabolic steroid, stabilizes Numb protein through inhibition of mdm2 in C2C12 myoblasts

Zika Virus Induces Degradation of the Numb Protein Required through Embryonic Neurogenesis

Zika virus (ZIKV) is a mosquito-borne flavivirus and causes an infection associated with congenital Zika syndrome and Guillain-Barre syndrome. The mechanism of ZIKV-mediated neuropathogenesis is not well understood. In this study, we discovered that ZIKV induces degradation of the Numb protein, which plays a crucial role in neurogenesis by allowing asymmetric cell division during embryonic development. Our data show that ZIKV reduced the Numb protein level in a time- and dose-dependent manner. However, ZIKV infection appears to have minimal effect on the Numb transcript. Treatment of ZIKV-infected cells with a proteasome inhibitor restores the Numb protein level, which suggests the involvement of the ubiquitin-proteasome pathway. In addition, ZIKV infection shortens the half-life of the Numb protein. Among the ZIKV proteins, the capsid protein significantly reduces the Numb protein level. Immunoprecipitation of the Numb protein co-precipitates the capsid protein, indicating the interaction between these two proteins. These results provide insights into the ZIKV-cell interaction that might contribute to its impact on neurogenesis.

Loss of Numb promotes hepatic progenitor expansion and intrahepatic cholangiocarcinoma by enhancing Notch signaling

Numb, a stem cell fate determinant, acts as a tumor suppressor and is closely related to a wide variety of malignancies. Intrahepatic cholangiocarcinoma (iCCA) originates from hepatic progenitors (HPCs); however, the role of Numb in HPC malignant transformation and iCCA development is still unclear. A retrospective cohort study indicated that Numb was frequently decreased in tumor tissues and suggests poor prognosis in iCCA patients. Consistently, in a chemically induced iCCA mouse model, Numb was downregulated in tumor cells compared to normal cholangiocytes. In diet-induced chronic liver injury mouse models, Numb ablation significantly promoted histological impairment, HPC expansion, and tumorigenesis. Similarly, Numb silencing in cultured iCCA cells enhanced cell spheroid growth, invasion, metastasis, and the expression of stem cell markers. Mechanistically, Numb was found to bind to the Notch intracellular domain (NICD), and Numb ablation promoted Notch signaling; this effect was reversed when Notch signaling was blocked by γ-secretase inhibitor treatment. Our results suggested that loss of Numb plays an important role in promoting HPC expansion, HPC malignant transformation, and, ultimately, iCCA development in chronically injured livers. Therapies targeting suppressed Numb are promising for the treatment of iCCA.

Anticancer activity and mechanism of total saponins from the residual seed cake of Camellia oleifera Abel. in hepatoma-22 tumor-bearing mice

Total saponins from the residual seed cake of Camellia oleifera Abel. exhibited beneficial properties on anticancer activity in hepatoma-22 tumor-bearing mice and represents a promising species for food applications.

Nandrolone-induced nuclear accumulation of MyoD protein is mediated by Numb, a Notch inhibitor, in C2C12 myoblasts

Signaling via the androgen receptor (AR) stimulates myogenic progenitor differentiation. In addition, myogenic differentiation factor D (MyoD) and Numb, a Notch inhibitor, play key roles in regulating myogenic differentiation. Nandrolone, an anabolic steroid, upregulates both MyoD and Numb expression in myogenic cells. However, the molecular mechanisms by which MyoD is upregulated by nandrolone are unclear. Moreover, the potential crosstalk between nandrolone, MyoD, and Numb is not well understood. With these considerations in mind, we examined the effects of nandrolone on the expression of MyoD mRNA and protein, and determined the interactions of MyoD and Numb in the presence or absence of nandrolone in differentiating C2C12 myoblasts. Nandrolone increased MyoD mRNA and protein expression and significantly enhanced nuclear translocation of MyoD protein. The later effect of nandrolone was blunted by siRNA against Numb. Immunoprecipitation (IP) studies confirmed that Numb forms complexes with MyoD. Chromatin IP revealed that in the presence of nandrolone, Numb is recruited to a region of the MyH7 promotor containing the E‐box to which MyoD binds. These data indicate that nandrolone‐regulated MyoD activation occurs mainly through a posttranslational mechanism which promotes MyoD nuclear accumulation, and suggest that this effect of nandrolone is, at least in part, mediated by Numb.

Natural products targeting the p53-MDM2 pathway and mutant p53: Recent advances and implications in cancer medicine

The p53 tumor suppressor plays a major role in controlling the initiation and development of cancer by regulating cell cycle arrest, apoptosis, senescence, and DNA repair. The MDM2 oncogene is a major negative regulator of p53 that inhibits the activity of p53 and reduces its protein stability. MDM2, p53, and the p53-MDM2 pathway represent well-documented targets for preventing and/or treating cancer. Natural products, especially those from medicinal and food plants, are a rich source for the discovery and development of novel therapeutic and preventive agents against human cancers. Many natural product-derived MDM2 inhibitors have shown potent efficacy against various human cancers. In contrast to synthetic small-molecule MDM2 inhibitors, the majority of which have been designed to inhibit MDM2-p53 binding and activate p53, many natural product inhibitors directly decrease MDM2 expression and/or MDM2 stability, exerting their anticancer activity in both p53-dependent and p53-independent manners. More recently, several natural products have been reported to target mutant p53 in cancer. Therefore, identification of natural products targeting MDM2, mutant p53, and the p53-MDM2 pathway can provide a promising strategy for the development of novel cancer chemopreventive and chemotherapeutic agents. In this review, we focus our discussion on the recent advances in the discovery and development of anticancer natural products that target the p53-MDM2 pathway, emphasizing several emerging issues, such as the efficacy, mechanism of action, and specificity of these natural products.

Thyroid hormone upregulates MDM2 in rat type I fibre: Implications for skeletal muscle mass regulation

AIM

Based upon a microarray assay, we have identified that triiodothyronine (T3) upregulates MDM2 gene expression in the rat skeletal muscle. As MDM2 protein is an E3 ligase, we hypothesized that this enzyme could play a role in T3 effects on skeletal muscle mass control.

METHODS

To test our hypothesis, male rats (2 months old) were randomly assigned into the following groups: intact controls, treated with 20 physiological doses of T3 for 0.5, 1 and 7 days, or with 5, 20 and 50 physiological doses of T3 for 7 days. For in vitro experiments, myotubes and C2C12 cells were treated with T3 for 3 days.

RESULTS

After validation of the microarray finding throughout RT-PCR and confirmation that T3 induces increases in MDM2 protein expression in a dose-dependent manner, we observed that MDM2 was upregulated by T3 exclusively in fibre type I. Moreover, detailed histological evaluation showed that MDM2 overexpression distributes punctiformily along the cross section of the fibre and also inside nuclei. MDM2 colocalizes with PAX7 in control muscle and T3 downregulates this myogenic factor. Pharmacological inhibition of MDM2 in cultured myotubes caused a severe decrease in their diameter (~35%, P < .001 vs Control), enhancing the effect of T3 (from ~12% to ~35%, P < .001) alone upon myotube diameter and mRNA levels of atrogenes. Finally, we observed that FOXO3 (MDM2 target) is kept outside the nucleus under T3 stimulation.

CONCLUSION

Our results indicate that MDM2 might be involved in the pro-trophic effects of T3 in skeletal muscle.

The role of sex steroid hormones in the pathophysiology and treatment of sarcopenia

Sex steroids influence the maintenance and growth of muscles. Decline in androgens, estrogens and progesterone by aging leads to the loss of muscular function and mass, sarcopenia. These steroid hormones can interact with different signaling pathways through their receptors. To date, sex steroid hormone receptors and their exact roles are not completely defined in skeletal and smooth muscles. Although numerous studies focused on the effects of sex steroid hormones on different types of cells, still many unexplained molecular mechanisms in both skeletal and smooth muscle cells remain to be investigated. In this paper, many different molecular mechanisms that are activated or inhibited by sex steroids and those that influence the growth, proliferation, and differentiation of skeletal and smooth muscle cells are reviewed. Also, the similarities of cellular and molecular pathways of androgens, estrogens and progesterone in both skeletal and smooth muscle cells are highlighted. The reviewed signaling pathways and participating molecules can be targeted in the future development of novel therapeutics.

Bringing androgens up a NOTCH in breast cancer

While it has been known for decades that androgen hormones influence normal breast development and breast carcinogenesis, the underlying mechanisms have only been recently elucidated. To date, most studies have focused on androgen action in breast cancer cell lines, yet these studies represent artificial systems that often do not faithfully replicate/recapitulate the cellular, molecular and hormonal environments of breast tumours in vivo. It is critical to have a better understanding of how androgens act in the normal mammary gland as well as in in vivo systems that maintain a relevant tumour microenvironment to gain insights into the role of androgens in the modulation of breast cancer development. This in turn will facilitate application of androgen-modulation therapy in breast cancer. This is particularly relevant as current clinical trials focus on inhibiting androgen action as breast cancer therapy but, depending on the steroid receptor profile of the tumour, certain individuals may be better served by selectively stimulating androgen action. Androgen receptor (AR) protein is primarily expressed by the hormone-sensing compartment of normal breast epithelium, commonly referred to as oestrogen receptor alpha (ERa (ESR1))-positive breast epithelial cells, which also express progesterone receptors (PRs) and prolactin receptors and exert powerful developmental influences on adjacent breast epithelial cells. Recent lineage-tracing studies, particularly those focussed on NOTCH signalling, and genetic analysis of cancer risk in the normal breast highlight how signalling via the hormone-sensing compartment can influence normal breast development and breast cancer susceptibility. This provides an impetus to focus on the relationship between androgens, AR and NOTCH signalling and the crosstalk between ERa and PR signalling in the hormone-sensing component of breast epithelium in order to unravel the mechanisms behind the ability of androgens to modulate breast cancer initiation and growth.

Ankrd1 is a transcriptional repressor for the androgen receptor that is downregulated by testosterone

The ankryn repeat domain proteins, Ankrd1 and Ankrd2, are expressed at the highest levels in skeletal muscle and heart where they are localized to the I band of the sarcomere through binding to titin and myopaladin. Ankrd1 and Ankrd2 migrate from the sarcomere to the nucleus when muscle is stressed, and act as coregulators for a growing number of transcription factors. Expression of Ankrd1 is altered by castration suggesting a link to androgen action. This investigation explored the effects of testosterone on Ankrd1 and Ankrd2 expression and determined whether Ankrd1 or Ankrd2 binds to or regulates the transcriptional activity of the androgen receptor (AR). Incubation of rat L6 myoblasts expressing the human AR (L6.AR) with testosterone reduced mRNA levels for Ankrd1 by approximately 50% and increased those for Ankrd2 by 20-fold. In reporter gene assays conducted with CHO cells co-transfected with an ARE-Luc reporter gene, Ankrd1 blocked the ability of testosterone to increase reporter gene activity while Ankrd2 had no effect. The effect of Ankrd1 and Ankrd2 on repression of the MAFbx promoter by testosterone was also tested in C2C12 cells using an MAFbx-Luc reporter gene (pMAF400-Luc); Ankrd1 blocked repression of pMAF400-Luc by testosterone while Ankrd2 did not. Co-immunoprecipitation studies revealed that Ankrd1 bound to the AR whereas Ankrd2 did not. The effect of Ankrd1 or Ankrd2 on changes in gene expression induced by testosterone in L6.AR cells was also evaluated. Incubation of L6.AR cells with testosterone modestly reduced myogenin mRNA levels but did not significantly alter those for mdm2, MEF2d, TnnI1, TnnI2, or p21. When cells were transfected with Ankrd1, testosterone markedly reduced mRNA levels for MEF2d, myogenin, p21 and TnnI1, increased those for TnnI2, but did not alter those for mdm2. When cells were transfected with Ankrd2, testosterone increased MEF2d and myogenin mRNA levels, having the opposite effect to cells transfected with Ankrd1; Ankrd2 did not change the effects of testosterone on TnnI1, TnnI2, p21, or mdm2 mRNA levels. In conclusion, testosterone regulates the expression of Ankrd1 and Ankrd2; Ankrd1 binds to and directly regulates the transcriptional activity of the AR whereas Ankrd2 does not; expression levels of both Ankrd1 and Ankrd2 modulate effects of testosterone on gene expression in cultured myoblasts.

Androgens up-regulate transcription of the Notch inhibitor Numb in C2C12 myoblasts via Wnt/β-catenin signaling to T cell factor elements in the Numb promoter

Androgen signaling via the androgen receptor is a key pathway that contributes to development, cell fate decisions, and differentiation, including that of myogenic progenitors. Androgens and synthetic steroids have well established anabolic actions on skeletal muscle. Wnt and Notch signaling pathways are also essential to myogenic cell fate decisions during development and tissue repair. However, the interactions among these pathways are largely unknown. Androgenic regulation of Wnt signaling has been reported. Nandrolone, an anabolic steroid, has been shown to inhibit Notch signaling and up-regulate Numb, a Notch inhibitor. To elucidate the mechanisms of interaction between nandrolone and Wnt/Notch signaling, we investigated the effects of nandrolone on Numb expression and Wnt signaling and determined the roles of Wnt signaling in nandrolone-induced Numb expression in C2C12 myoblasts. Nandrolone increased Numb mRNA and protein levels and T cell factor (Tcf) transcriptional activity via inhibition of glycogen synthase kinase 3β. Up-regulation of Numb expression by nandrolone was blocked by the Wnt inhibitors, sFRP1 and DKK1, whereas Wnt3a increased Numb mRNA and protein expression. In addition, we observed that the proximal promoter of the Numb gene had functional Tcf binding elements to which β-catenin was recruited in a manner enhanced by both nandrolone and Wnt3a. Moreover, site-directed mutagenesis indicated that the Tcf binding sites in the Numb promoter are required for the nandrolone-induced Numb transcriptional activation in this cell line. These results reveal a novel molecular mechanism underlying up-regulation of Numb transcription with a critical role for increased canonical Wnt signaling. In addition, the data identify Numb as a novel target gene of the Wnt signaling pathway by which Wnts would be able to inhibit Notch signaling.