Cytoplasmic polyadenylation element binding protein is a conserved target of tumor suppressor HRPT2/CDC73

The roles of the tumor suppressor parafibromin in cancer

In this review, we discuss parafibromin protein, which is encoded by CDC73. A mutation in this gene causes hyperparathyroidism-jaw tumor (HPT-JT) syndrome, an autosomal dominant disease. CDC73 is transcriptionally downregulated by the Wilms’ tumor suppressor gene WT1 and translationally targeted by miR-182-3p and miR-155. In the nucleus, parafibromin binds to RNA polymerase II and PAF1 complex for transcription. Parafibromin transcriptionally increases the expression of c-Myc, decreases CPEB1 expression by interacting with H3M4, and reduces cyclin D1 expression by binding to H3K9. The RNF20/RNF40/parafibromin complex induces monoubiquitination of H2B-K120, and SHP2-mediated dephosphorylation of parafibromin promotes the parafibromin/β-catenin interaction and induces the expression of Wnt target genes, which is blocked by PTK6-medidated phosphorylation. Parafibromin physically associates with the CPSF and CstF complexes that are essential for INTS6 mRNA maturation. In the cytosol, parafibromin binds to hSki8 and eEF1Bγ for the destabilization of p53 mRNA, to JAK1/2-STAT1 for STAT1 phosphorylation, and to actinin-2/3 to bundle/cross-link actin filaments. Mice with CDC73 knockout in the parathyroid develop parathyroid and uterine tumors and are used as a model for HPT-JT syndrome. Conditional deletion of CDC73 in mesenchymal progenitors results in embryos with agenesis of the heart and liver while its abrogation in mature osteoblasts and osteocytes increases cortical and trabecular bone. Heterozygous germline mutations in CDC73 are associated with parathyroid carcinogenesis. The rates of CDC73 mutation and parafibromin loss decrease from parathyroid adenoma to atypical adenoma to carcinoma. In addition, down-regulated parafibromin is closely linked to the tumorigenesis, subsequent progression, or poor prognosis of head and neck, gastric, lung, colorectal, and ovarian cancers, and its overexpression might reverse the aggressiveness of these cancer cells. Therefore, parafibromin might be useful as a biological marker of malignancies and a target for their gene therapy.

Micro RNAs Promoting Growth and Metastasis in Preclinical In Vivo Models of Subcutaneous Melanoma

During the last years a considerable therapeutic progress in melanoma patients with the RAF V600E mutation via RAF/MEK pathway inhibition and immuno-therapeutic modalities has been witnessed. However, the majority of patients relapse after therapy. Therefore, a deeper understanding of the pathways driving oncogenicity and metastasis of melanoma is of paramount importance. In this review, we summarize microRNAs modulating tumor growth, metastasis, or both, in preclinical melanoma-related in vivo models and possible clinical impact in melanoma patients as modalities and targets for treatment of melanoma. We have identified miR-199a (ApoE, DNAJ4), miR-7-5p (RelA), miR-98a (IL6), miR-219-5p (BCL2) and miR-365 (NRP1) as possible targets to be scrutinized in further target validation studies.

Cataloguing and Selection of mRNAs Localized to Dendrites in Neurons and Regulated by RNA-Binding Proteins in RNA Granules

Spatiotemporal translational regulation plays a key role in determining cell fate and function. Specifically, in neurons, local translation in dendrites is essential for synaptic plasticity and long-term memory formation. To achieve local translation, RNA-binding proteins in RNA granules regulate target mRNA stability, localization, and translation. To date, mRNAs localized to dendrites have been identified by comprehensive analyses. In addition, mRNAs associated with and regulated by RNA-binding proteins have been identified using various methods in many studies. However, the results obtained from these numerous studies have not been compiled together. In this review, we have catalogued mRNAs that are localized to dendrites and are associated with and regulated by the RNA-binding proteins fragile X mental retardation protein (FMRP), RNA granule protein 105 (RNG105, also known as Caprin1), Ras-GAP SH3 domain binding protein (G3BP), cytoplasmic polyadenylation element binding protein 1 (CPEB1), and staufen double-stranded RNA binding proteins 1 and 2 (Stau1 and Stau2) in RNA granules. This review provides comprehensive information on dendritic mRNAs, the neuronal functions of mRNA-encoded proteins, the association of dendritic mRNAs with RNA-binding proteins in RNA granules, and the effects of RNA-binding proteins on mRNA regulation. These findings provide insights into the mechanistic basis of protein-synthesis-dependent synaptic plasticity and memory formation and contribute to future efforts to understand the physiological implications of local regulation of dendritic mRNAs in neurons.

The mitochondrial calcium uniporter contributes to morphine tolerance through pCREB and CPEB1 in rat spinal cord dorsal horn

BACKGROUND

The long-term use of opioid analgesics is limited by the development of unwanted side-effects, such as tolerance. The molecular mechanisms of morphine anti-nociceptive tolerance are still unclear. The mitochondrial calcium uniporter (MCU) is involved in painful hyperalgesia, but the role of MCU in morphine tolerance has not been uncharacterised.

METHODS

Rats received intrathecal injection of morphine for 7 days to induce morphine tolerance. The mechanical withdrawal threshold was measured using von Frey filaments, and thermal latency using the hotplate test. The effects of an MCU inhibitor, antisense oligodeoxynucleotide against cyclic adenosine monophosphate response element (CRE)-binding protein (CREB) or cytoplasmic polyadenylation element-binding protein 1 (CPEB1) in morphine tolerance were examined.

RESULTS

Spinal morphine tolerance was associated with an increased expression of neuronal MCU, phospho-CREB (pCREB), and CPEB1 in the spinal cord dorsal horn. MCU inhibition increased the mechanical threshold and thermal latency, and reduced the accumulation of mitochondrial calcium in morphine tolerance. Intrathecal antisense oligodeoxynucleotide against CREB or CPEB1 restored the anti-nociceptive effects of morphine compared with mismatch oligodeoxynucleotide in von Frey test and hotplate test. Chromatin immunoprecipitation with quantitative PCR assay showed that CREB knockdown reduced the interaction of pCREB with the ccdc109a gene (encoding MCU expression) promoter and decreased the MCU mRNA transcription. RNA immunoprecipitation assay suggested that CPEB1 binds to the MCU mRNA 3' untranslated region. CPEB1 knockdown decreased the expression of MCU protein.

CONCLUSIONS

These findings suggest that spinal MCU is regulated by pCREB and CPEB1 in morphine tolerance, and that inhibition of MCU, pCREB, or CPEB1 may be useful in preventing the development of opioid tolerance.

Down-regulation of cancer-associated gene CDC73 contributes to cellular senescence

Dysregulated gene expression is another important contributor in explaining cancer-related phenotypes in addition to mutations. Cellular senescence is a mechanism for the prevention of cancer and thus it is important to understand the regulation of gene expression in senescence due to its potential in anti-cancer therapy. Here, we found that CDC73, which encodes the cell division cycle 73 and acts as a tumor suppressor, was unexpectedly up-regulated in several cancer types but down-regulated in a variety of senescent cells. Importantly, depletion of CDC73 could induce senescence-associated phenotypes in both normal and cancer cells, with an increase in p21 expression. In terms of molecular mechanism, alternative polyadenylation (APA)-mediated 3' untranslated region (3' UTR) lengthening explained, at least in part, the decreased CDC73 expression in senescent cells because longer 3' UTR had a higher rate of RNA degradation compared to the shorter one. Our work discovered that post-transcriptional down-regulation of CDC73 contributed to cellular senescence.

Reduced adenosine-to-inosine miR-455-5p editing promotes melanoma growth and metastasis

Although recent studies have shown that adenosine-to-inosine (A-to-I) RNA editing occurs in microRNAs, its effects on tumor growth and metastasis are not well understood. We present evidence of CREB-mediated low expression of ADAR1 in metastatic melanoma cell lines and tumor specimens. Re-expression of ADAR1 resulted in the suppression of melanoma growth and metastasis in vivo. Consequently, we identified 3 miRs undergoing A-to-I editing in the low-metastatic melanoma but not in highly metastatic cell lines. One of these miRs, miR-455-5p has two A-to-I RNA editing sites. The biological function of edited miR-455-5p is different from the unedited form as it recognizes different set of genes. Indeed, w.t. miR-455-5p promotes melanoma metastasis via inhibition of the tumor suppressor gene CPEB1. Moreover, w.t. miR-455 enhances melanoma growth and metastasis in vivo while the edited form inhibits these features. These results demonstrate a previously unrecognized role of RNA editing in melanoma progression.

Structure and function of pre-mRNA 5'-end capping quality control and 3'-end processing

Messenger RNA precursors (pre-mRNAs) are produced as the nascent transcripts of RNA polymerase II (Pol II) in eukaryotes and must undergo extensive maturational processing, including 5′-end capping, splicing, and 3′-end cleavage and polyadenylation. This review will summarize the structural and functional information reported over the past few years on the large machinery required for the 3′-end processing of most pre-mRNAs, as well as the distinct machinery for the 3′-end processing of replication-dependent histone pre-mRNAs, which have provided great insights into the proteins and their subcomplexes in these machineries. Structural and biochemical studies have also led to the identification of a new class of enzymes (the DXO family enzymes) with activity toward intermediates of the 5′-end capping pathway. Functional studies demonstrate that these enzymes are part of a novel quality surveillance mechanism for pre-mRNA 5′-end capping. Incompletely capped pre-mRNAs are produced in yeast and human cells, in contrast to the general belief in the field that capping always proceeds to completion, and incomplete capping leads to defects in splicing and 3′-end cleavage in human cells. The DXO family enzymes are required for the detection and degradation of these defective RNAs.

CPEB1 promotes differentiation and suppresses EMT in mammary epithelial cells

Downregulation of CPEB1, a sequence-specific RNA-binding protein, in a mouse mammary epithelial cell line (CID-9) causes epithelial-to-mesenchymal transition (EMT), based on several criteria. First, CPEB1 knockdown decreases protein levels of E-cadherin and β-catenin but increases those of vimentin and Twist1. Second, the motility of CPEB1-depleted cells is increased. Third, CID-9 cells normally form growth-arrested, polarized and three-dimensional acini upon culture in extracellular matrix, but CPEB1-deficient CID-9 cells form nonpolarized proliferating colonies lacking a central cavity. CPEB1 downregulates Twist1 expression by binding to its mRNA, shortening its poly(A) tract and repressing its translation. CID-9 cultures contain both myoepithelial and luminal epithelial cells. CPEB1 increases during CID-9 cell differentiation, is predominantly expressed in myoepithelial cells, and its knockdown prevents expression of the myoepithelial marker p63. CPEB1 is present in proliferating subpopulations of pure luminal epithelial cells (SCp2) and myoepithelial cells (SCg6), but its depletion increases Twist1 only in SCg6 cells and fails to downregulate E-cadherin in SCp2 cells. We propose that myoepithelial cells prevent EMT by influencing the polarity and proliferation of luminal epithelial cells in a mechanism that requires translational silencing of myoepithelial Twist1 by CPEB1.

Translational control of cell growth and malignancy by the CPEBs

The cytoplasmic polyadenylation element binding proteins (CPEBs) associate with specific sequences in mRNA 3' untranslated regions to promote translation. They do so by inducing cytoplasmic polyadenylation, which requires specialized poly(A) polymerases. Aberrant expression of these proteins correlates with certain types of cancer, indicating that cytoplasmic RNA 3' end processing is important in the control of growth. Several CPEB-regulated mRNAs govern cell cycle progression, regulate senescence, establish cell polarity, and promote tumorigenesis and metastasis. In this Opinion article, we discuss the emerging evidence that indicates a key role for the CPEBs in cancer biology.

Cell cycle-regulatory cyclins and their deregulation in oral cancer

Oral cancer is a growth-related disorder, and cyclins are the prime regulators of cell division. Cyclins are associated with the pathogenesis of oral cancer and are considered valuable biomarkers for diagnosis and prognosis. These important molecules are regulated in many ways to achieve a gain in function and are involved in promoting neoplastic growth. While the causes of most cyclin overexpression are varied, these cyclins may be induced by buccal mucosal insult mainly with carcinogens that alter various pathways propelling oral cancer. Substantial experimental evidences support a link between oncogenic signaling pathways and the deregulation of cyclins in oral cancer. This review focuses on the mechanisms by which cyclins are regulated and promote oral oncogenesis.

The many roles of the conserved eukaryotic Paf1 complex in regulating transcription, histone modifications, and disease states

The Paf1 complex was originally identified over fifteen years ago in budding yeast through its physical association with RNA polymerase II. The Paf1 complex is now known to be conserved throughout eukaryotes and is well studied for promoting RNA polymerase II transcription elongation and transcription-coupled histone modifications. Through these critical regulatory functions, the Paf1 complex participates in numerous cellular processes such as gene expression and silencing, RNA maturation, DNA repair, cell cycle progression and prevention of disease states in higher eukaryotes. In this review, we describe the historic and current research involving the eukaryotic Paf1 complex to explain the cellular roles that underlie its conservation and functional importance. This article is part of a Special Issue entitled: RNA polymerase II Transcript Elongation.

The CPEB-family of proteins, translational control in senescence and cancer

Cytoplasmic elongation of the poly(A) tail was originally identified as a mechanism to activate maternal mRNAs, stored as silent transcripts with short poly(A) tails, during meiotic progression. A family of RNA-binding proteins named CPEBs, which recruit the translational repression or cytoplasmic polyadenylation machineries to their target mRNAs, directly mediates cytoplasmic polyadenylation. Recent years have witnessed an explosion of studies showing that CPEBs are not only expressed in a variety of somatic tissues, but have essential functions controlling gene expression in time and space in the adult organism. These "new" functions of the CPEBs include regulating the balance between senescence and proliferation and its pathological manifestation, tumor development. In this review, we summarize current knowledge on the functions of the CPEB-family of proteins in the regulation of cell proliferation, their target mRNAs and the mechanism controlling their activities.

The EIF4EBP3 translational repressor is a marker of CDC73 tumor suppressor haploinsufficiency in a parathyroid cancer syndrome

Germline mutation of the tumor suppressor gene CDC73 confers susceptibility to the hyperparathyroidism-jaw tumor syndrome associated with a high risk of parathyroid malignancy. Inactivating CDC73 mutations have also been implicated in sporadic parathyroid cancer, but are rare in sporadic benign parathyroid tumors. The molecular pathways that distinguish malignant from benign parathyroid transformation remain elusive. We previously showed that a hypomorphic allele of hyrax (hyx), the Drosophila homolog of CDC73, rescues the loss-of-ventral-eye phenotype of lobe, encoding the fly homolog of Akt1s1/ PRAS40. We report now an interaction between hyx and Tor, a central regulator of cell growth and autophagy, and show that eukaryotic translation initiation factor 4E-binding protein (EIF4EBP), a translational repressor and effector of mammalian target of rapamycin (mTOR), is a conserved target of hyx/CDC73. Flies heterozygous for Tor and hyx, but not Mnn1, the homolog of the multiple endocrine neoplasia type 1 (MEN1) tumor suppressor associated with benign parathyroid tumors, are starvation resistant with reduced basal levels of Thor/4E-BP. Human peripheral blood cell levels of EIF4EBP3 were reduced in patients with CDC73, but not MEN1, heterozygosity. Chromatin immunoprecipitation demonstrated occupancy of EIF4EBP3 by endogenous parafibromin. These results show that EIF4EBP3 is a peripheral marker of CDC73 function distinct from MEN1-regulated pathways, and suggest a model whereby starvation resistance and/or translational de-repression contributes to parathyroid malignant transformation.