Roles of BCCIP deficiency in mammary tumorigenesis

Ergolide mediates anti-cancer effects on metastatic uveal melanoma cells and modulates their cellular and extracellular vesicle proteomes

Background

Uveal melanoma is a poor prognosis cancer. Ergolide, a sesquiterpene lactone isolated from Inula Brittanica, exerts anti-cancer properties. The objective of this study was to 1) evaluate whether ergolide reduced metastatic uveal melanoma (MUM) cell survival/viability in vitro and in vivo; and 2) to understand the molecular mechanism of ergolide action.

Methods

Ergolide bioactivity was screened via long-term proliferation assay in UM/MUM cells and in zebrafish MUM xenograft models. Mass spectrometry profiled proteins modulated by ergolide within whole cell or extracellular vesicle (EVs) lysates of the OMM2.5 MUM cell line. Protein expression was analyzed by immunoblots and correlation analyses to UM patient survival used The Cancer Genome Atlas (TCGA) data.

Results

Ergolide treatment resulted in significant, dose-dependent reductions (48.5 to 99.9%; p<0.0001) in OMM2.5 cell survival in vitro and of normalized primary zebrafish xenograft fluorescence (56%; p<0.0001) in vivo, compared to vehicle controls. Proteome-profiling of ergolide-treated OMM2.5 cells, identified 5023 proteins, with 52 and 55 proteins significantly altered at 4 and 24 hours, respectively ( p<0.05; fold-change >1.2). Immunoblotting of heme oxygenase 1 (HMOX1) and growth/differentiation factor 15 (GDF15) corroborated the proteomic data. Additional proteomics of EVs isolated from OMM2.5 cells treated with ergolide, detected 2931 proteins. There was a large overlap with EV proteins annotated within the Vesiclepedia compendium. Within the differentially expressed proteins, the proteasomal pathway was primarily altered. Interestingly, BRCA2 and CDKN1A Interacting Protein (BCCIP) and Chitinase Domain Containing 1 (CHID1), were the only proteins significantly differentially expressed by ergolide in both the OMM2.5 cellular and EV isolates and they displayed inverse differential expression in the cells versus the EVs.

Conclusions

Ergolide is a novel, promising anti-proliferative agent for UM/MUM. Proteomic profiling of OMM2.5 cellular/EV lysates identified candidate pathways elucidating the action of ergolide and putative biomarkers of UM, that require further examination.

Ergolide mediates anti-cancer effects on metastatic uveal melanoma cells and modulates their cellular and extracellular vesicle proteomes

BACKGROUND

Uveal melanoma is a poor prognosis cancer. Ergolide, a sesquiterpene lactone isolated from Inula Brittanica, exerts anti-cancer properties. The objective of this study was to 1) evaluate whether ergolide reduced metastatic uveal melanoma (MUM) cell survival/viability in vitro and in vivo; and 2) to understand the molecular mechanism of ergolide action.

METHODS

Ergolide bioactivity was screened via long-term proliferation assay in UM/MUM cells and in zebrafish MUM xenograft models. Mass spectrometry profiled proteins modulated by ergolide within whole cell or extracellular vesicle (EVs) lysates of the OMM2.5 MUM cell line. Protein expression was analyzed by immunoblots and correlation analyses to UM patient survival used The Cancer Genome Atlas (TCGA) data.

RESULTS

Ergolide treatment resulted in significant, dose-dependent reductions (48.5 to 99.9%; p<0.0001) in OMM2.5 cell survival in vitro and of normalized primary zebrafish xenograft fluorescence (56%; p<0.0001) in vivo, compared to vehicle controls. Proteome-profiling of ergolide-treated OMM2.5 cells, identified 5023 proteins, with 52 and 55 proteins significantly altered at 4 and 24 hours, respectively ( p<0.05; fold-change >1.2). Immunoblotting of heme oxygenase 1 (HMOX1) and growth/differentiation factor 15 (GDF15) corroborated the proteomic data. Additional proteomics of EVs isolated from OMM2.5 cells treated with ergolide, detected 2931 proteins. There was a large overlap with EV proteins annotated within the Vesiclepedia compendium. Within the differentially expressed proteins, the proteasomal pathway was primarily altered. Interestingly, BRCA2 and CDKN1A Interacting Protein (BCCIP) and Chitinase Domain Containing 1 (CHID1), were the only proteins significantly differentially expressed by ergolide in both the OMM2.5 cellular and EV isolates and they displayed inverse differential expression in the cells versus the EVs.

CONCLUSIONS

Ergolide is a novel, promising anti-proliferative agent for UM/MUM. Proteomic profiling of OMM2.5 cellular/EV lysates identified candidate pathways elucidating the action of ergolide and putative biomarkers of UM, that require further examination.

The BRCA2 and CDKN1A-interacting protein (BCCIP) stabilizes stalled replication forks and prevents degradation of nascent DNA

DNA replication stress is characterized by impaired replication fork progression, causing some of the replication forks to collapse and form DNA breaks. It is a primary cause of genomic instability leading to oncogenic transformation. The repair-independent functions of the proteins RAD51 and BRCA2, which are involved in homologous recombination (HR)-mediated DNA repair, are crucial for protecting nascent DNA strands from nuclease-mediated degradation. The BRCA2 and CDKN1A-interacting protein (BCCIP) associates with BRCA2 and RAD51 during HR-mediated DNA repair. Here, we investigated the role of BCCIP during the replication stress response. We find that in the presence of replication stress, BCCIP deficiency increases replication fork stalling and results in DNA double-strand break formation. We show that BCCIP is recruited to stalled replication forks and prevents MRE11 nuclease-mediated degradation of nascent DNA strands.

Metadherin (AEG-1/MTDH/LYRIC) expression: Significance in malignancy and crucial role in colorectal cancer

Metadherin (AEG-1/MTDH/LYRIC) is a 582-amino acid transmembrane protein, encoded by a gene located at chromosome 8q22, and distributed throughout the cytoplasm, peri-nuclear region, nucleus, and nucleolus as well as the endoplasmic reticulum (ER). It contains several structural and interacting domains through which it interacts with transcription factors such as nuclear factor-κB (NF-κB), promyelocytic leukemia zinc finger (PLZF), staphylococcal nuclease domain containing 1 (SND1) and lung homing domain (LHD). It is regulated by miRNAs and mediates its oncogenic function via activation of cell proliferation, survival, migration and metastasis, as well as, angiogenesis and chemoresistance via phosphatidylinositol-3-kinase/AKT (PI3K/AKT), NF-κB, mitogen-activated protein kinase (MAPK) and Wnt signaling pathways. In this chapter, metadherin is reviewed highlighting its role in mediating growth, metastasis and chemoresistance in colorectal cancer (CRC). Metadherin, as well as its variants, and antibodies are associated with CRC progression, poorer prognosis, decreased survival and advanced clinico-pathology. The potential of AEG-1/MTDH/LYRIC as a diagnostic and prognostic marker as well as a therapeutic target in CRC is explored.

Phospho-Ku70 induced by DNA damage interacts with RNA Pol II and promotes the formation of phospho-53BP1 foci to ensure optimal cNHEJ

Canonical non-homologous end-joining (cNHEJ) is the prominent mammalian DNA double-strand breaks (DSBs) repair pathway operative throughout the cell cycle. Phosphorylation of Ku70 at ser27-ser33 (pKu70) is induced by DNA DSBs and has been shown to regulate cNHEJ activity, but the underlying mechanism remained unknown. Here, we established that following DNA damage induction, Ku70 moves from nucleoli to the sites of damage, and once linked to DNA, it is phosphorylated. Notably, the novel emanating functions of pKu70 are evidenced through the recruitment of RNA Pol II and concomitant formation of phospho-53BP1 foci. Phosphorylation is also a prerequisite for the dynamic release of Ku70 from the repair complex through neddylation-dependent ubiquitylation. Although the non-phosphorylable ala-Ku70 form does not compromise the formation of the NHEJ core complex per se, cells expressing this form displayed constitutive and stress-inducible chromosomal instability. Consistently, upon targeted induction of DSBs by the I-SceI meganuclease into an intrachromosomal reporter substrate, cells expressing pKu70, rather than ala-Ku70, are protected against the joining of distal DNA ends. Collectively, our results underpin the essential role of pKu70 in the orchestration of DNA repair execution in living cells and substantiated the way it paves the maintenance of genome stability.

BCCIP is required for nucleolar recruitment of eIF6 and 12S pre-rRNA production during 60S ribosome biogenesis

Ribosome biogenesis is a fundamental process required for cell proliferation. Although evolutionally conserved, the mammalian ribosome assembly system is more complex than in yeasts. BCCIP was originally identified as a BRCA2 and p21 interacting protein. A partial loss of BCCIP function was sufficient to trigger genomic instability and tumorigenesis. However, a complete deletion of BCCIP arrested cell growth and was lethal in mice. Here, we report that a fraction of mammalian BCCIP localizes in the nucleolus and regulates 60S ribosome biogenesis. Both abrogation of BCCIP nucleolar localization and impaired BCCIP-eIF6 interaction can compromise eIF6 recruitment to the nucleolus and 60S ribosome biogenesis. BCCIP is vital for a pre-rRNA processing step that produces 12S pre-rRNA, a precursor to the 5.8S rRNA. However, a heterozygous Bccip loss was insufficient to impair 60S biogenesis in mouse embryo fibroblasts, but a profound reduction of BCCIP was required to abrogate its function in 60S biogenesis. These results suggest that BCCIP is a critical factor for mammalian pre-rRNA processing and 60S generation and offer an explanation as to why a subtle dysfunction of BCCIP can be tumorigenic but a complete depletion of BCCIP is lethal.

Requirement of Bccip for the Regeneration of Intestinal Progenitors

BCCIP was originally identified as a BRCA2 and CDKN1A/p21 interaction protein. Although a partial loss of BCCIP function is sufficient to trigger genomic instability and tumorigenesis, complete deletion of BCCIP is lethal to cells. Using Rosa26-CreERT2 mouse models, we found that induced Bccip deletion in adult mice caused an acute intestinal epithelial denudation that cannot be relieved by co-deletion of Trp53. The critical role of Bccip in intestine epithelial renewal was verified with a Villin-CreERT2 mouse model. The epithelium degeneration was associated with a rapid loss of the proliferative capability of the crypt progenitor cells in vivo, lack of crypt base columnar stem cell markers, and a failure of in vitro crypt organoid growth. RNA-Seq analysis of freshly isolated intestinal crypt cells showed that Bccip deletion caused an overwhelming down-regulation of genes involved in mitotic cell division but an up-regulation of genes involved in apoptosis and stress response to microbiomes. Our data not only indicate that intestinal epithelium is the most sensitive tissue to whole-body deletion of Bccip but also point to Bccip as a novel and critical factor for the proliferation of the intestinal progenitors. These findings have significant implications for understanding why a hypomorphic loss of BCCIP functions is more relevant to tumorigenesis.

Spontaneous Development of Hepatocellular Carcinoma and B-Cell Lymphoma in Mosaic and Heterozygous Brca2 and Cdkn1a Interacting Protein Knockout Mice

Hepatocellular carcinoma (HCC) is the most common form of liver tumors. Although HCC is associated with chronic viral infections, alcoholic cirrhosis, and nonalcoholic fatty liver disease, genetic factors that contribute to the HCC risk remain unknown. The BRCA2 DNA repair associated (BRCA2) and cyclin-dependent kinase inhibitor 1A (CDKN1A) interacting protein, known as BCCIP, are essential for cell viability and maintenance of genomic stability. In this study, we established a new genetically engineered mouse model with Bccip deficiency. Mosaic or heterozygous Bccip deletion conferred an increased risk of spontaneous liver tumorigenesis and B-cell lymphoma development at old age. These abnormalities are accompanied with chronic inflammation, histologic features of nonalcoholic steatohepatitis, keratin and ubiquitin aggregates within cytoplasmic Mallory-Denk bodies, and changes of the intracellular distribution of high-mobility group box 1 protein. Our study suggests BCCIP dysregulation as a risk factor for HCC and offers a novel mouse model for future investigations of nonviral or nonalcoholic causes of HCC development.

The Penaeus stylirostris densovirus capsid protein interacts with the Litopenaeus vannamei BCCIP protein

Viral capsid proteins play an important role in the viral infection process. To identify the cellular proteins in shrimp that interact with the Penaeus stylirostris densovirus capsid protein (PstDNV-CP), we constructed a yeast two-hybrid (Y2H) cDNA library of the muscle tissue of Litopenaeus vannamei, and hybridized the bait vector pGBKT7-CP with this library. Cloning and sequencing showed that the shrimp protein interacting with PstDNV-CP was a homolog of BRCA2 and CDKN1A(p21)-interacting protein (BCCIP). We named this protein L. vannamei BCCIP (LvBCCIP). Further analysis showed that LvBCCIP interacted with L. vannamei calmodulin (LvCaM). We validated the interactions between PstDNV-CP and LvBCCIP, and between LvBCCIP and LvCaM, with GST pulldown assays. The gene expression of LvBCCIP increased significantly after PstDNV challenge. In addition, the PstDNV titer of PstDNV-challenged shrimp was significantly reduced after LvBCCIP expression was inhibited using double-stranded RNA (dsRNA) interference. These results indicated that LvBCCIP is critical to PstDNV pathogenesis in L. vannamei. Interestingly, the growth rate of L. vannamei was significantly reduced when LvBCCIP gene expression was silenced, indicating that LvBCCIP may also be associated with growth regulation in L. vannamei. Thus, the interaction between PstDNV-CP and LvBCCIP might explain why PstDNV infection leads to runt-deformity syndrome in shrimp.