RESUMEN
Heterogeneous ribonuclear protein A18 (hnRNP A18) is an RNA binding protein (RBP) involved in the hypoxic cellular stress response and regulation of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) expression in melanoma, breast cancer, prostate cancer, and colon cancer solid tumors. hnRNP A18 is comprised of an N-terminal structured RNA recognition motif (RMM) and a C-terminal intrinsically disordered domain (IDD). Upon cellar stressors, such as UV and hypoxia, hnRNP A18 is phosphorylated by casein kinase 2 (CK2) and glycogen synthase kinase 3ß (GSK-3ß). After phosphorylation, hnRNP A18 translocates from the nucleus to the cytosol where it interacts with pro-survival mRNA transcripts for proteins such as hypoxia inducible factor 1α and CTLA-4. Both the hypoxic cellular response and modulation of immune checkpoints by cancer cells promote chemoradiation resistance and metastasis. In this study, the 1 H, 13 C, and 15 N backbone and sidechain resonances of the 172 amino acid hnRNP A18 were assigned sequence-specifically and provide a framework for future NMR-based drug discovery studies toward targeting hnRNP A18. These data will also enable the investigation of the dynamic structural changes within the IDD of hnRNP A18 upon phosphorylation by CK2 and GSK-3ß to provide critical insight into the structure and function of IDDs.
Asunto(s)
Proteínas Portadoras , Ribonucleoproteínas Nucleares Heterogéneas , Masculino , Humanos , ARN Mensajero/metabolismo , Glucógeno Sintasa Quinasa 3 beta/metabolismo , Antígeno CTLA-4/metabolismo , Proteínas Portadoras/metabolismo , Resonancia Magnética Nuclear Biomolecular , Ribonucleoproteínas Nucleares Heterogéneas/genética , Ribonucleoproteínas Nucleares Heterogéneas/metabolismo , Unión ProteicaRESUMEN
The heterogeneous ribonucleoprotein A18 (hnRNP A18) is upregulated in hypoxic regions of various solid tumors and promotes tumor growth via the coordination of mRNA transcripts associated with pro-survival genes. Thus, hnRNP A18 represents an important therapeutic target in tumor cells. Presented here is the first X-ray crystal structure to be reported for the RNA-recognition motif of hnRNP A18. By comparing this structure with those of homologous RNA-binding proteins (i.e. hnRNP A1), three residues on one face of an antiparallel ß-sheet (Arg48, Phe50 and Phe52) and one residue in an unstructured loop (Arg41) were identified as likely to be involved in protein-nucleic acid interactions. This structure helps to serve as a foundation for biophysical studies of this RNA-binding protein and structure-based drug-design efforts for targeting hnRNP A18 in cancer, such as malignant melanoma, where hnRNP A18 levels are elevated and contribute to disease progression.