Harold C. Smith, Ph.D.

Normal and cancer cells express more diversity in proteins than can be accounted for by the predicted number of expressed genomic DNA sequence. Expansion of the genomically encoded expressed sequences through alternative processing of RNA, such as mRNA editing, is a logical hypothesis for how protein diversity and variations seen as tissue-specific and regulated expression of proteins can be achieved. The specific focus of the research is to identify and characterize novel mammalian mRNA editing systems that employ a zinc-dependent deamination mechanism for the post-transcriptional conversion of cytidine to uridine at select sites within mRNAs. Computational modeling has suggested a family of mammalian enzymes known as Cytidine Deaminases Active on RNA or CDARs as responsible for C to U editing of mRNAs.

The expression of these enzymes in biology suggests that mRNA editing may be involved in numerous physiological processes and could be manipulated for the prevention of cardiovascular disease, HIV infection and cancer, and is also necessary for production of antibodies in B lymphocytes. Recent evidence indicates that the enzyme involved in suppressing HIV-1 infectivity (CEM15) and the enzyme that promotes antibody production (AID) may act to mutate deoxy cytidine in DNA rather than or in addition to RNA.

Our research involves molecular biology and protein techniques, DNA microarray analyses and computational biology to identify the mRNAs that are edited by CDARs and to determine the biological consequence of these editing events in terms of the predicted changes in the types of protein structures and functions that can be expressed. Our studies have demonstrated how cytidine to uridine mRNA editing contributes to expansion in the diversity of expressed mRNA sequences known collectively as the transcriptome.

We are also evaluating the regulatory mechanisms controlling the expression of editing factors and their localization in the cell nucleus. The development of this new information will establish an important new annotation of the human genome that will serve as a frame of reference for studies of proteins involved in health and disease and mechanisms regulating their expression.