Research

My laboratory is attempting to define the physiological role and mechanism of regulation of Casein Kinase II (CKII), a ubiquitous and highly conserved member of the eukaryotic Ser/Thr/Tyr protein kinase family. We have used two model systems in exploring this problem, Drosophila melanogaster and Saccharomyces cerevisiae, and are currently focusing on the latter.

Overview

The secondary modification of proteins by reversible phosphorylation is a major mechanism of protein regulation in eukaryotic cells. The protein kinases and phosphatases that catalyze this reversible modification often constitute integral components of signal transduction cascades that mediate both intracellular homeostasis and extracellular signalling. Interference with the activity of these enzymes, either biochemically or genetically, potentially results in altered cell function and disease. As one example, protein phosphorylation plays a pivotal role in both cell cycle regulation and growth control, and mutation of the protein kinases or phosphatases (or their regulators) involved in these processes often leads to unregulated cell proliferation and cancer.

Casein kinase II (CKII) is a highly conserved Ser/Thr protein kinase that is ubiquitous among eukaryotic organisms. Observations from a number of laboratories suggest a role for this enzyme in human cancer: 1) CKII phosphorylates a broad spectrum of endogenous substrates, including known oncoproteins and tumor suppressors, 2) CKII activity is elevated in rapidly dividing normal cells, transformed cells in culture, and solid human tumors, and 3) dysregulated expression of CKII in lymphocytes of transgenic mice results in the stochastic production of lymphomas and, in combination with overexpression of c-myc, in the production of leukemia. Unfortunately, neither the mechanism of regulation nor the physiological role of CKII has been defined in any system. My laboratory is using biochemical, molecular, genetic, cell biological, and genomic approaches to define the function and regulation of CKII in the budding yeast Saccharomyces cerevisiae.

My laboratory has purified yeast CKII to homogeneity, characterized the subunit composition and biochemical function of the purified enzyme in vitro, isolated the genes encoding each of the four enzyme subunits, constructed null and conditional mutations of these genes, characterized the resulting phenotypes, and isolated multicopy suppressors of some of these mutants. The results reveal that CKII is essential for viability in S. cerevisiae and required for diverse cellular functions, including cell cycle progression in both G1 and G2/M, maintenance of cell polarity, ion homeostasis, and gene expression. Among the genes identified via genetic interaction are a kinase-specific chaperone required for cell cycle progression (CDC37) and a gene pair intimately involved in cell polarity (ZDS1,2). We are currently employing genomic and proteomic strategies, such as transcriptional profiling and biochemical genomics, in order to define the global function of CKII.

The results obtained in the genetically tractable yeast system should yield parallel insights into the physiological role of CKII in higher systems, including man. Given the observations relating CKII to cancer, the results have potential for diagnosis and/or treatment of human disease.