C9orf10 protein, a novel protein component of Puralpha-containing mRNA-protein particles (Puralpha-mRNPs): characterization of developmental and regional expressions in the mouse brain

The ataxia-telangiectasia disease protein ATM controls vesicular protein secretion via CHGA and microtubule dynamics via CRMP5

The autosomal recessive disease ataxia-telangiectasia (A-T) presents with cerebellar degeneration, immunodeficiency, radiosensitivity, capillary dilatations, and pulmonary infections. Most symptoms outside the nervous system can be explained by failures of the disease protein ATM as a Ser/Thr-kinase to coordinate DNA damage repair. However, ATM in adult neurons has cytoplasmic localization and vesicle association, where its roles remain unclear. Here, we defined novel ATM protein targets in human neuroblastoma cells, and filtered initial pathogenesis events in ATM-null mouse cerebellum. Profiles of global proteome and phosphoproteomics - both direct ATM/ATR substrates and overall phosphorylation changes - confirmed previous findings for NBN, MRE11, MDC1, CHEK1, EIF4EBP1, AP3B2, PPP2R5C, SYN1 and SLC2A1. Even stronger downregulation of ATM/ATR substrate phosphopeptides after ATM-depletion was documented for CHGA, EXPH5, NBEAL2 and CHMP6 as key factors of protein secretion and endosome dynamics, as well as for CRMP5, DISP2, PHACTR1, PLXNC1, INA and TPX2 as neurite extension factors. Prominent effects on semaphorin-CRMP5-microtubule signals and ATM association with CRMP5 were validated. As a functional consequence, microtubules were stabilized, and neurite retraction ensued. The impact of ATM on secretory granules confirms previous ATM-null cerebellar transcriptome findings. This study provides the first link of A-T neural atrophy to growth cone collapse and aberrant microtubule dynamics.

FAM120A deficiency improves resistance to cisplatin in gastric cancer by promoting ferroptosis

The occurrence of chemoresistance is an inescapable obstacle affecting the clinical efficacy of cisplatin in gastric cancer (GC). Exploring the regulatory mechanism of cisplatin resistance will help to provide potential effective targets for improving the prognosis of gastric cancer patients. Here, we find that FAM120A is upregulated in GC tissues and higher in cisplatin-resistant GC tissues, and its high expression is positively correlated with the poor outcome of GC patients. Functional studies indicate that FAM120A confers chemoresistance to GC cells by inhibiting ferroptosis. Mechanically, METTL3-induced m6A modification and YTHDC1-induced stability of FAM120A mRNA enhance FAM120A expression. FAM120A inhibits ferroptosis by binding SLC7A11 mRNA and enhancing its stability. FAM120A deficiency enhances cisplatin sensitivity by promoting ferroptosis in vivo. These results reveal the function of FAM120A in chemotherapy tolerance and targeting FAM120A is an effective strategy to alleviate cisplatin resistance in GC.

Molecular mechanisms of schizophrenia: Insights from human genetics

Schizophrenia is a debilitating psychiatric disorder that affects millions of people worldwide; however, its etiology is poorly understood at the molecular and neurobiological levels. A particularly important advance in recent years is the discovery of rare genetic variants associated with a greatly increased risk of developing schizophrenia. These primarily loss-of-function variants are found in genes that overlap with those implicated by common variants and are involved in the regulation of glutamate signaling, synaptic function, DNA transcription, and chromatin remodeling. Animal models harboring mutations in these large-effect schizophrenia risk genes show promise in providing additional insights into the molecular mechanisms of the disease.

AGO-RBP crosstalk on target mRNAs: Implications in miRNA-guided gene silencing and cancer

MicroRNAs (miRNAs) and RNA-binding proteins (RBPs) are important regulators of mRNA translation and stability in eukaryotes. While miRNAs can only bind their target mRNAs in association with Argonaute proteins (AGOs), RBPs directly bind their targets either as single entities or in complex with other RBPs to control mRNA metabolism. miRNA binding in 3' untranslated regions (3' UTRs) of mRNAs facilitates an intricate network of interactions between miRNA-AGO and RBPs, thus determining the fate of overlapping targets. Here, we review the current knowledge on the interplay between miRNA-AGO and multiple RBPs in different cellular contexts, the rules underlying their synergism and antagonism on target mRNAs, as well as highlight the implications of these regulatory modules in cancer initiation and progression.

Sequestration of microRNA-mediated target repression by the Ago2-associated RNA-binding protein FAM120A

Argonaute (Ago) proteins interact with various binding partners and play a pivotal role in microRNA (miRNA)-mediated silencing pathways. By utilizing immunoprecipitation followed by mass spectrometry to determine cytoplasmic Ago2 protein complexes in mouse embryonic stem cells (mESCs), we identified a putative RNA-binding protein FAM120A (also known as OSSA/C9ORF10) as an Ago2 interacting protein. Individual nucleotide resolution cross-linking and immunoprecipitation (iCLIP) analysis revealed that FAM120A binds to homopolymeric tracts in 3'-UTRs of about 2000 mRNAs, particularly poly(G) sequences. Comparison of FAM120A iCLIP and Ago2 iCLIP reveals that greater than one-third of mRNAs bound by Ago2 in mESCs are co-bound by FAM120A. Furthermore, such FAM120A-bound Ago2 target genes are not subject to Ago2-mediated target degradation. Reporter assays suggest that the 3'-UTRs of several FAM120A-bound miRNA target genes are less sensitive to Ago2-mediated target repression than those of FAM120A-unbound miRNA targets and FAM120A modulates them via its G-rich target sites. These findings suggest that Ago2 may exist in multiple protein complexes with varying degrees of functionality.

A complex Xp11.22 deletion in a patient with syndromic autism: exploration of FAM120C as a positional candidate gene for autism

We present a male patient with sporadic Aarskog syndrome, cleft palate, mild intellectual disability, and autism spectrum disorder (ASD). A submicroscopic discontiguous deletion was detected on chromosome Xp11.2 encompassing FGD1, FAM120C, and PHF8. That the deletion encompassed FGD1 (exons 2-8) explains the Aarskog features while the deletion of PHF8 most likely explains the cleft palate and mild intellectual disability. We identify FAM120C as a novel X-linked candidate gene for autism for two reasons: first, a larger deletion encompassing FAM120C segregates with autism in a previously reported family and second, there is recent evidence that FAM120C interacts with CYFIP1, part of the FMRP (Fragile X Mental Retardation Protein) network. In the current study, resequencing of FAM120C in 87 Belgian male patients with autism spectrum disorder identified no novel mutations. Expression of Fam120c in mouse tissues showed enriched expression in pituitary, cerebellum, cortex, and pancreatic islets of Langerhans. Additionally, we found a cortical expression pattern of Fam120c similar to that of Fmr1. In conclusion, FAM120C is a novel candidate gene for autism spectrum disorder based on genetic evidence and the brain expression pattern. Thereby we highlight a role for FMRP network genes in ASD.

Proteogenomic analysis of human chromosome 9-encoded genes from human samples and lung cancer tissues

The Chromosome-centric Human Proteome Project (C-HPP) was recently initiated as an international collaborative effort. Our team adopted chromosome 9 (Chr 9) and performed a bioinformatics and proteogenomic analysis to catalog Chr 9-encoded proteins from normal tissues, lung cancer cell lines, and lung cancer tissues. Approximately 74.7% of the Chr 9 genes of the human genome were identified, which included approximately 28% of missing proteins (46 of 162) on Chr 9 compared with the list of missing proteins from the neXtProt Master Table (2013-09). In addition, we performed a comparative proteomics analysis between normal lung and lung cancer tissues. On the basis of the data analysis, 15 proteins from Chr 9 were detected only in lung cancer tissues. Finally, we conducted a proteogenomic analysis to discover Chr 9-residing single nucleotide polymorphisms (SNP) and mutations described in the COSMIC cancer mutation database. We identified 21 SNPs and four mutations containing peptides on Chr 9 from normal human cells/tissues and lung cancer cell lines, respectively. In summary, this study provides valuable information of the human proteome for the scientific community as part of C-HPP. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium with the data set identifier PXD000603.

Early induction of stress-associated Src activator/Homo sapiens chromosome 9 open reading frame 10 protein following photodynamic therapy

BACKGROUND

There are proteins, responsible for many basic cell functions (transmission of extracellular signals to cytoplasm or nucleus, cell growth, proliferation, migration, survival), which are activated and overexpressed in response to acute oxidative stress, especially tyrosine kinases. The oxidative stress-associated Src activator/Homo sapiens chromosome 9 open reading frame 10 protein (Ossa/C9orf10) protects cancer cells from oxidative stress-induced apoptosis by Src family kinases activation.

METHODS

In this study precursor of protoporphyrin IX, 5-aminolevulinic acid and its encapsulated form were used in treating MCF-7 human breast cancer cells. After light illumination, cells were collected at different time points and used for evaluation (immunocytochemistry, Western blot analysis) of expression of above proteins, c-Src and Ossa.

RESULTS

Our results showed that 5-aminolevulinic acid-mediated photodynamic therapy caused decrease of c-Src expression at 7h after irradiation. The strongest expression was observed at 24h after treatment. Encapsulated form of 5-aminolevulinic acid in terms of PDT caused similar changes of expression of c-Src protein. Furthermore, we observed strong Ossa expression at 7h after treatment in comparison to very low expression at time points 0, 18 and 24h.

CONCLUSION

We would like to emphasize that our results showed high expression of Ossa at early time interval after PDT, which was accompanied by a low expression of c-Src kinase, what could protect cancer cells from PDT through activation of c-Src in response to oxidative stress.

The pur protein family: genetic and structural features in development and disease

The Pur proteins are an ancient family of sequence-specific single-stranded nucleic acid-binding proteins. They bind a G-rich element in either single- or double-stranded nucleic acids and are capable of displacing the complementary C-rich strand. Recently several reports have described Pur family member knockouts, mutations, and disease aberrations. Together with a recent crystal structure of Purα, these data reveal conserved structural features of these proteins that have been adapted to serve functions unique to higher eukaryotes. In humans Pur proteins are critical for myeloid cell development, muscle development, and brain development, including trafficking of mRNA to neuronal dendrites. Pur family members have been implicated in diseases as diverse as cancer, premature aging, and fragile-X mental retardation syndrome.

Multiple roles for Puralpha in cellular and viral regulation

Pur-alpha is a ubiquitous multifunctional protein that is strongly conserved throughout evolution, binds to both DNA and RNA and functions in the initiation of DNA replication, control of transcription and mRNA translation. In addition, it binds to several cellular regulatory proteins including the retinoblastoma protein, E2F-1, Sp1, YB-1, cyclin T1/Cdk9 and cyclin A/Cdk2. These observations and functional studies provide evidence that Puralpha is a major player in the regulation of the cell cycle and oncogenic transformation. Puralpha also binds to viral proteins such as the large T-antigen of JC virus (JCV) and the Tat protein of human immunodeficiency virus-1 (HIV-1) and plays a role in the cross-communication of these viruses in the opportunistic polyomavirus JC (JCV) brain infection, progressive multifocal leukoencephalopathy (PML). The creation of transgenic mice with inactivation of the PURA gene that encodes Puralpha has revealed that Puralpha is critical for postnatal brain development and has unraveled an essential role of Puralpha in the transport of specific mRNAs to the dendrites and the establishment of the postsynaptic compartment in the developing neurons. Finally, the availability of cell cultures from the PURA knockout mice has allowed studies that have unraveled a role for Puralpha in DNA repair.

A novel RNA-binding protein, Ossa/C9orf10, regulates activity of Src kinases to protect cells from oxidative stress-induced apoptosis

During the process of tumor progression and clinical treatments, tumor cells are exposed to oxidative stress. Tumor cells are frequently resistant to such stress by producing antiapoptotic signaling, including activation of Src family kinases (SFKs), although the molecular mechanism is not clear. In an attempt to identify the SFK-binding proteins selectively phosphorylated in gastric scirrhous carcinoma, we identified an uncharacterized protein, C9orf10. Here we report that C9orf10 (designated Ossa for oxidative stress-associated Src activator) is a novel RNA-binding protein that guards cancer cells from oxidative stress-induced apoptosis by activation of SFKs. Exposure to oxidative stress such as UV irradiation induces the association of Ossa/C9orf10 with regulatory domains of SFKs, which activates these kinases and causes marked tyrosine phosphorylation of C9orf10 in turn. Tyrosine-phosphorylated Ossa recruits p85 subunits of phosphatidylinositol 3-kinase (PI3-kinase) and behaves as a scaffolding protein for PI3-kinase and SFKs, which activates the Akt-mediated antiapoptotic pathway. On the other hand, the carboxyl terminus of Ossa has a distinct function that directly binds RNAs such as insulin-like growth factor II (IGF-II) mRNA and promotes the extracellular secretion of IGF-II. Our findings indicate that Ossa is a dual-functional protein and might be a novel therapeutic target which modulates the sensitivity of tumors to oxidative stress.