Biophysical characterization and modeling of human Ecdysoneless (ECD) protein supports a scaffolding function

ECD functions as a novel RNA-binding protein to regulate mRNA splicing

The human ecdysoneless protein (ECD) plays an essential role in the regulation of cell cycle and cell survival. ECD has been implicated in RNA splicing through its association with the protein components of splicing complex. Here, using electrophoretic mobility shift assay and mutational analysis, we demonstrate that ECD directly binds to RNA through its N-terminal region, specifically using amino acids 135-148. Using enhanced CLIP-seq analyses in human cells, we identified a large repertoire of mRNAs bound to ECD. RNA-seq analyses revealed that ECD depletion in cells leads to widespread RNA splicing aberrations associated with alterations in gene expression. Significantly, we demonstrate that ECD mediates mRNA splicing by directly binding to RNA sequences located near splicing sites. Mechanistically, we demonstrate that ECD directly binds to U5 small nuclear RNA (snRNA), and this interaction is critical for maintaining the expression of key protein components of U5 small nuclear protein (snRNP) complex. Notably, RNA binding defective mutant of ECD fails to rescue downregulated levels of U5 snRNP components or cell proliferation block induced by ECD knockout. Collectively, we provide compelling evidence that ECD regulates RNA splicing by directly associating with RNAs, and the RNA binding activity of ECD is essential for its function.

Ecdysoneless Overexpression Drives Mammary Tumorigenesis through Upregulation of C-MYC and Glucose Metabolism

Ecdysoneless (ECD) protein is essential for embryogenesis, cell-cycle progression, and cellular stress mitigation with an emerging role in mRNA biogenesis. We have previously shown that ECD protein as well as its mRNA are overexpressed in breast cancer and ECD overexpression predicts shorter survival in patients with breast cancer. However, the genetic evidence for an oncogenic role of ECD has not been established. Here, we generated transgenic mice with mammary epithelium-targeted overexpression of an inducible human ECD transgene (ECDTg). Significantly, ECDTg mice develop mammary hyperplasia, preneoplastic lesions, and heterogeneous tumors with occasional lung metastasis. ECDTg tumors exhibit epithelial to mesenchymal transition and cancer stem cell characteristics. Organoid cultures of ECDTg tumors showed ECD dependency for in vitro oncogenic phenotype and in vivo growth when implanted in mice. RNA sequencing (RNA-seq) analysis of ECDTg tumors showed a c-MYC signature, and alterations in ECD levels regulated c-MYC mRNA and protein levels as well as glucose metabolism. ECD knockdown-induced decrease in glucose uptake was rescued by overexpression of mouse ECD as well as c-MYC. Publicly available expression data analyses showed a significant correlation of ECD and c-MYC overexpression in breast cancer, and ECD and c-MYC coexpression exhibits worse survival in patients with breast cancer. Taken together, we establish a novel role of overexpressed ECD as an oncogenesis driver in the mouse mammary gland through upregulation of c-MYC-mediated glucose metabolism.

IMPLICATIONS

We demonstrate ECD overexpression in the mammary gland of mice led to the development of a tumor progression model through upregulation of c-MYC signaling and glucose metabolism.

The Role of Hsp90-R2TP in Macromolecular Complex Assembly and Stabilization

Hsp90 is a ubiquitous molecular chaperone involved in many cell signaling pathways, and its interactions with specific chaperones and cochaperones determines which client proteins to fold. Hsp90 has been shown to be involved in the promotion and maintenance of proper protein complex assembly either alone or in association with other chaperones such as the R2TP chaperone complex. Hsp90-R2TP acts through several mechanisms, such as by controlling the transcription of protein complex subunits, stabilizing protein subcomplexes before their incorporation into the entire complex, and by recruiting adaptors that facilitate complex assembly. Despite its many roles in protein complex assembly, detailed mechanisms of how Hsp90-R2TP assembles protein complexes have yet to be determined, with most findings restricted to proteomic analyses and in vitro interactions. This review will discuss our current understanding of the function of Hsp90-R2TP in the assembly, stabilization, and activity of the following seven classes of protein complexes: L7Ae snoRNPs, spliceosome snRNPs, RNA polymerases, PIKKs, MRN, TSC, and axonemal dynein arms.

Ecdysoneless Protein Regulates Viral and Cellular mRNA Splicing to Promote Cervical Oncogenesis

High-risk human papillomaviruses (HPV), exemplified by HPV16/18, are causally linked to human cancers of the anogenital tract, skin, and upper aerodigestive tract. Previously, we identified Ecdysoneless (ECD) protein, the human homolog of the Drosophila ecdysoneless gene, as a novel HPV16 E6-interacting protein. Here, we show that ECD, through its C-terminal region, selectively binds to high-risk but not to low-risk HPV E6 proteins. We demonstrate that ECD is overexpressed in cervical and head and neck squamous cell carcinoma (HNSCC) cell lines as well as in tumor tissues. Using The Cancer Genome Atlas dataset, we show that ECD mRNA overexpression predicts shorter survival in patients with cervical and HNSCC. We demonstrate that ECD knockdown in cervical cancer cell lines led to impaired oncogenic behavior, and ECD co-overexpression with E7 immortalized primary human keratinocytes. RNA-sequencing analyses of SiHa cells upon ECD knockdown showed to aberrations in E6/E7 RNA splicing, as well as RNA splicing of several HPV oncogenesis-linked cellular genes, including splicing of components of mRNA splicing machinery itself. Taken together, our results support a novel role of ECD in viral and cellular mRNA splicing to support HPV-driven oncogenesis. IMPLICATIONS: This study links ECD overexpression to poor prognosis and shorter survival in HNSCC and cervical cancers and identifies a critical role of ECD in cervical oncogenesis through regulation of viral and cellular mRNA splicing.

The Mammalian Ecdysoneless Protein Interacts with RNA Helicase DDX39A To Regulate Nuclear mRNA Export

The mammalian orthologue of ecdysoneless (ECD) protein is required for embryogenesis, cell cycle progression, and mitigation of endoplasmic reticulum stress. Here, we identified key components of the mRNA export complexes as binding partners of ECD and characterized the functional interaction of ECD with key mRNA export-related DEAD BOX protein helicase DDX39A. We find that ECD is involved in RNA export through its interaction with DDX39A. ECD knockdown (KD) blocks mRNA export from the nucleus to the cytoplasm, which is rescued by expression of full-length ECD but not an ECD mutant that is defective in interaction with DDX39A. We have previously shown that ECD protein is overexpressed in ErbB2⁺ breast cancers (BC). In this study, we extended the analyses to two publicly available BC mRNA The Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) data sets. In both data sets, ECD mRNA overexpression correlated with short patient survival, specifically ErbB2⁺ BC. In the METABRIC data set, ECD overexpression also correlated with poor patient survival in triple-negative breast cancer (TNBC). Furthermore, ECD KD in ErbB2⁺ BC cells led to a decrease in ErbB2 mRNA level due to a block in its nuclear export and was associated with impairment of oncogenic traits. These findings provide novel mechanistic insight into the physiological and pathological functions of ECD.