Cyclin D1 and C/EBPβ LAP1 operate in a common pathway to promote mammary epithelial cell differentiation

Expression and Activity of the Transcription Factor CCAAT/Enhancer-Binding Protein β (C/EBPβ) Is Regulated by Specific Pulse-Modulated Radio Frequencies in Oligodendroglial Cells

The rapid growth of wireless electronic devices has raised concerns about the harmful effects of leaked electromagnetic radiation (EMR) on human health. Even though numerous studies have been carried out to explore the biological effects of EMR, no clear conclusions have been drawn about the effect of radio frequency (RF) EMR on oligodendrocytes. To this end, we exposed oligodendroglia and three other types of brain cells to 2.4 GHz EMR for 6 or 48 h at an average input power of 1 W in either a continuous wave (CW-RF) or a pulse-modulated wave (PW-RF, 50 Hz pulse frequency, 1/3 duty cycle) pattern. RNA sequencing, RT-qPCR, and Western blot were used to examine the expression of C/EBPβ and its related genes. Multiple reaction monitoring (MRM) was used to examine the levels of expression of C/EBPβ-interacting proteins. Our results showed that PW-RF EMR significantly increased the mRNA level of C/EBPβ in oligodendroglia but not in other types of cells. In addition, the expression of three isoforms and several interacting proteins and targeted genes of C/EBPβ were markedly changed after 6-h PW-RF but not CW-RF. Our results indicated that RF EMR regulated the expression and functions of C/EBPβ in a waveform- and cell-type-dependent manner.

Emerging functions of C/EBPβ in breast cancer

Breast tumorigenesis relies on complex interactions between tumor cells and their surrounding microenvironment, orchestrated by tightly regulated transcriptional networks. C/EBPβ is a key transcription factor that regulates the proliferation and differentiation of multiple cell types and modulates a variety of biological processes such as tissue homeostasis and the immune response. In addition, C/EBPβ has well-established roles in mammary gland development, is overexpressed in breast cancer, and has tumor-promoting functions. In this review, we discuss context-specific roles of C/EBPβ during breast tumorigenesis, isoform-specific gene regulation, and regulation of the tumor immune response. We present challenges in C/EBPβ biology and discuss the importance of C/EBPβ isoform-specific gene regulation in devising new therapeutic strategies.

Exercise rejuvenates quiescent skeletal muscle stem cells in old mice through restoration of Cyclin D1

Aging impairs tissue repair. This is pronounced in skeletal muscle, whose regeneration by muscle stem cells (MuSCs) is robust in young adult animals but inefficient in older organisms. Despite this functional decline, old MuSCs are amenable to rejuvenation through strategies that improve the systemic milieu, such as heterochronic parabiosis. One such strategy, exercise, has long been appreciated for its benefits on healthspan, but its effects on aged stem cell function in the context of tissue regeneration are incompletely understood. Here we show that exercise in the form of voluntary wheel running accelerates muscle repair in old animals and improves old MuSC function. Through transcriptional profiling and genetic studies, we discovered that the restoration of old MuSC activation ability hinges on restoration of Cyclin D1, whose expression declines with age in MuSCs. Pharmacologic studies revealed that Cyclin D1 maintains MuSC activation capacity by repressing TGFβ signaling. Taken together, these studies demonstrate that voluntary exercise is a practicable intervention for old MuSC rejuvenation. Furthermore, this work highlights the distinct role of Cyclin D1 in stem cell quiescence.

C/EBPß Isoform Specific Gene Regulation: It's a Lot more Complicated than you Think!

It has been almost 30 years since C/EBPß was discovered. Seminal studies have shown that C/EBPß is a master regulator of mammary gland development and has been shown to control and influence proliferation and differentiation through varying mechanisms. The single-exon C/EBPß mRNA yields at least three different protein isoforms which have diverse, specific, context-dependent, and often non-overlapping roles throughout development and breast cancer progression. These roles are dictated by a number of complex factors including: expression levels of other C/EBP family members and their stoichiometry relative to the isoform in question, binding site affinity, post-translational modifications, co-factor expression, and even hormone levels and lactogenic status. Here we summarize the historical work up to the latest findings in the field on C/EBPß in the mammary gland and in breast cancer. With the current emphasis on improving immunotherapy in breast cancer the role of specific C/EBPß isoforms in regulating specific chemokine and cytokine expression and the immune microenvironment will be of increasing interest.

Bta-miR-130a regulates the biosynthesis of bovine milk fat by targeting peroxisome proliferator-activated receptor gamma

Milk fat determines the quality of milk and is also a main targeted trait in dairy cow breeding. Recent studies have revealed important regulatory roles of microRNAs (miRNA) in milk fat synthesis in the mammary gland. However, the role of miRNA in bovine mammary epithelial cells (BMEC) remains largely unknown. In this study, we found that the overexpression of miR-130a significantly decreased cellular triacylglycerol (TAG) levels and suppressed lipid droplet formation, whereas the inhibition of miR-130a resulted in greater lipid droplet formation and TAG accumulation in BMEC. MiR-130a also significantly affected mRNA expression related to milk fat metabolism. Specifically, the overexpression of miR-130a reduced the mRNA expression of , , , and , whereas the downregulation of miR-130a increased the mRNA expression of , , , , , and . Furthermore, western blot analysis revealed the protein level of PPARG in miR-130a mimic and inhibitor transfection groups to be consistent with the mRNA expression response. Finally, luciferase reporter assays verified that PPARG was the direct target of miR-130a. This study provides the first experimental evidence that miR-130a directly affects TAG synthesis in BMEC by targeting PPARG, suggesting that miR-130a potentially could be used to improve beneficial milk components in dairy cows.

CCAAT/enhancer binding protein β negatively regulates progesterone receptor expression in human glioblastoma cells

Many progesterone (P4) actions are mediated by its intracellular receptor (PR), which has two isoforms (PR-A and PR-B) differentially transcribed from separate promoters of a single gene. In glioblastomas, the most frequent and aggressive brain tumors, PR-B is the predominant isoform. In an in silico analysis we showed putative CCAAT/Enhancer Binding Protein (C/EBP) binding sites at PR-B promoter. We evaluated the role of C/EBPβ in PR-B expression regulation in glioblastoma cell lines, which expressed different ratios of PR and C/EBPβ isoforms (LAP1, LAP2, and LIP). ChIP assays showed a significant basal binding of C/EBPβ, specific protein 1 (Sp1) and estrogen receptor alpha (ERα) to PR-B promoter. C/EBPβ knockdown increased PR-B expression and treatment with estradiol (E2) reduced C/EBPβ binding to the promoter and up-regulated PR-B expression. P4 induced genes were differently regulated when CEBP/β was silenced. These data show that C/EBPβ negatively regulates PR-B expression in glioblastoma cells.

Tyrosine receptor kinase B is a drug target in astrocytomas

BACKGROUND

Astrocytomas are the most common primary human brain tumors. Receptor tyrosine kinases (RTKs), including tyrosine receptor kinase B (TrkB, also known as tropomyosin-related kinase B; encoded by neurotrophic tyrosine kinase receptor type 2 [NTRK2]), are frequently mutated by rearrangement/fusion in high-grade and low-grade astrocytomas. We found that activated TrkB can contribute to the development of astrocytoma and might serve as a therapeutic target in this tumor type.

METHODS

To identify RTKs capable of inducing astrocytoma formation, a library of human tyrosine kinases was screened for the ability to transform murine Ink4a^-/-/Arf^-/- astrocytes. Orthotopic allograft studies were conducted to evaluate the effects of RTKs on the development of astrocytoma. Since TrkB was identified as a driver of astrocytoma formation, the effect of the Trk inhibitors AZD1480 and RXDX-101 was assessed in astrocytoma cells expressing activated TrkB. RNA sequencing, real-time PCR, western blotting, and enzyme-linked immunosorbent assays were conducted to characterize NTRK2 in astrocytomas.

RESULTS

Activated TrkB cooperated with Ink4a/Arf loss to induce the formation of astrocytomas through a mechanism mediated by activation of signal transducer and activator of transcription 3 (STAT3). TrkB activation positively correlated with Ccl2 expression. TrkB-induced astrocytomas remained dependent on TrkB signaling for survival, highlighting a role of NTRK2 as an addictive oncogene. Furthermore, the QKI-NTRK2 fusion associated with human astrocytoma transformed Ink4a^-/-/Arf^-/- astrocytes, and this process was also mediated via STAT3 signaling.

CONCLUSIONS

Our findings provide evidence that constitutively activated NTRK2 alleles, notably the human tumor-associated QKI-NTRK2 fusion, can cooperate with Ink4a/Arf loss to drive astrocytoma formation. Therefore, we propose NTRK2 as a potential therapeutic target in the subset of astrocytoma patients defined by QKI-NTRK2 fusion.

Orosomucoid 2 inhibits tumor metastasis and is upregulated by CCAAT/enhancer binding protein β in hepatocellular carcinomas

Cancer metastasis is a complex process, and the incidence of metastasis is influenced by many biological factors. Orosomucoid 2 (ORM2) is an important glycoprotein that is mainly biosynthesized and secreted by hepatocytes. As an acute-phase protein, ORM2 likely plays important roles in anti-inflammation, immunomodulation and drug delivery. However, little is known regarding the function of ORM2 in hepatocellular carcinoma (HCC). In this study, we determined that ORM2 expression in HCC tissues was negatively associated with intrahepatic metastasis and histological grade. Moreover, the ectopic overexpression of ORM2 decreased HCC cell migration and invasion in vitro and intrahepatic metastasis in vivo, whereas silencing ORM2 expression resulted in increased tumor cell migration and invasion in vitro. The CCAAT/enhancer binding protein β (C/EBPβ) upregulated ORM2 expression, while only the LAP1/2 (C/EBPβ isoforms) possessed transcription-promoting activity on the ORM2 promoter. Subsequently, we found that LAP1 repressed HCC cell migration and invasion via the induction of ORM2 expression. Consistently, the protein expression of C/EBPβ was negatively associated with histological grade and positively correlated with ORM2 protein expression in HCC tissues. Collectively, our findings indicate that ORM2 is a functional downstream target of C/EBPβ and functions as a tumor suppressor in HCC.

Non-canonical functions of cell cycle cyclins and cyclin-dependent kinases

The roles of cyclins and their catalytic partners, the cyclin-dependent kinases (CDKs), as core components of the machinery that drives cell cycle progression are well established. Increasing evidence indicates that mammalian cyclins and CDKs also carry out important functions in other cellular processes, such as transcription, DNA damage repair, control of cell death, differentiation, the immune response and metabolism. Some of these non-canonical functions are performed by cyclins or CDKs, independently of their respective cell cycle partners, suggesting that there was a substantial divergence in the functions of these proteins during evolution.

Hormone-sensing mammary epithelial progenitors: emerging identity and hormonal regulation

The hormone-sensing mammary epithelial cell (HS-MEC-expressing oestrogen receptor-alpha (ERα) and progesterone receptor (PGR)) is often represented as being terminally differentiated and lacking significant progenitor activity after puberty. Therefore while able to profoundly influence the proliferation and function of other MEC populations, HS-MECs are purported not to respond to sex hormone signals by engaging in significant cell proliferation during adulthood. This is a convenient and practical simplification that overshadows the sublime, and potentially critical, phenotypic plasticity found within the adult HS-MEC population. This concept is exemplified by the large proportion (~80 %) of human breast cancers expressing PGR and/or ERα, demonstrating that HS-MECs clearly proliferate in the context of breast cancer. Understanding how HS-MEC proliferation and differentiation is driven could be key to unraveling the mechanisms behind uncontrolled HS-MEC proliferation associated with ERα- and/or PGR-positive breast cancers. Herein we review evidence for the existence of a HS-MEC progenitor and the emerging plasticity of the HS-MEC population in general. This is followed by an analysis of hormones other than oestrogen and progesterone that are able to influence HS-MEC proliferation and differentiation: androgens, prolactin and transforming growth factor-beta1.