Pilot: Post Transcriptional Control of Ribosomal Proteins in Hematopoietic Neoplasia

Principal Investigator: Garcia, Eric 18.2 2. PROJECT TITLE: Post transcriptional control of ribosomal proteins in hematopoietic neoplasia. ABSTRACT: Ribosomal proteins are core components of the ribosome that dynamically integrate cell signals with protein synthesis. Mutations in genes encoding ribosomal proteins cause a heterogeneous group of diseases, termed ribosomopathies. Ribosomopathies are tissue-specific diseases that predispose affected individuals to cancer. Myelodysplastic syndromes (MDS) are a subset of ribosomopathies that exhibit disruptions to ribosomal protein and spliceosomal protein biology. MDS have a high predisposition to evolve into acute myeloid leukemia (AML). The Drosophila melanogaster ribosomal protein S21 (RpS21) is an archetypical example of RP proteins. The Drosophila RpS21 protein is highly homologous to the human protein, and, more intriguingly, their transcripts share an exceptionally-conserved alternative splicing pattern. Dysregulated expression of human RPS21 has been linked to various types of cancer. Disruptive transposon insertions in the fly RpS21 gene cause similar phenotypes as loss of other fly ribosomal protein coding genes; however, loss of RpS21 in flies also causes a cancer-like overgrowth of hematopoietic organs. Thus, Drosophila RpS21 is uniquely well-suited to serve as a model for the role of the ribosome in MDS and leukemia. The conserved alternative splicing pattern of RpS21 transcripts leads to a small change of only two amino acids at the carboxy-terminal end of the encoded protein. These alternative isoforms provide a notable opportunity to study a normal mechanism for regulating overall ribosome levels and/or composition. The overall hypothesis is that alternative splicing of RpS21 transcripts tunes the ribosome to alternative splicing cues. The narrow central hypothesis for this proposal is that alternative splicing of RpS21 transcripts modifies levels of total RpS21 protein. The objectives of this proposal are: 1) to uncover how alternative splicing of RpS21 transcripts affects RpS21 protein levels and functions and 2) to determine the in vivo abundance of RpS21 transcripts relative to the proliferative capacity of different cells and tissues. To address these objectives, we propose one specific aim: 1) determine the ability of individual RpS21 protein isoforms to functionally complement RpS21 depletion. This specific aim will provide the foundation for our use of fly RpS21 to model normal ribosome homeostasis and MDS. The overgrowth of hematopoietic organs exhibited by fly RpS21 mutants make it an ideal system to model the contribution of dual dysregulations to ribosomal proteins and alternative splicing to cancer progression. Institutional Research Grant American Cancer Society – January 2019