David Siderovski

Background

Siderovski was born in Toronto, Ontario to Thelma and Angelo Sideris. He was the youngest of two children.

Education

Siderovski attended Earl Haig Secondary School in North York, Ontario where he graduated in 1985.

In 1989, Siderovski graduated with a Bachelor of Science (Honours) degree from Queen's University in Kingston, Ontario. He majored in biochemistry and received the Prince of Wales Prize awarded to the one student graduating with an honours B.Sc. degree who is judged to have the best academic record at Queen's in that year's graduating class.

Siderovski began his Ph.D training at the University of Toronto in May 1989. During his fifth year of Ph.D training, he also began full-time work as a Research Scientist in the Quantitative Biology Laboratory of the Amgen Research Institute (Toronto, Canada). He successfully defended his PhD thesis in November 1997. He left the Amgen Research Institute in December 1998, after having contributed to three patents as a co-inventor.

Early academic career

After completing his industrial postdoctoral position at the Amgen Research Institute in 1998, Siderovski joined the faculty at the University of North Carolina at Chapel Hill as a tenure-track Assistant Professor of Pharmacology. His earliest publications, starting with a brief original report in Current Biology, chronicle his independent discovery of the RGS protein superfamily and determinations of their varied protein structures and cellular functions. One of these early reports was co-authored by two Nobel laureates: Alfred G. Gilman and Robert Lefkowitz.

Discovery and characterizations of RGS proteins

Siderovski was the first to report the cloning and sequencing of a cDNA encoding an RGS protein family member: 'G0/G1-switch gene-8' or G0S8 (subsequently renamed RGS2); this cloning and sequencing work was conducted as a Queen's University undergraduate student in the Biochemistry laboratory of Dr. Donald R. Forsdyke. Before the discovery of RGS proteins, the duration of heterotrimeric G-protein signaling was thought to be modulated by only two factors: the intrinsic GTP hydrolysis rate of the Gα subunit and acceleration of that rate by some specialized Gα effectors (i.e., phospholipase C-beta isoforms). What Siderovski originally identified as the G0S8-homology ("GH") domain in proteins from several eukaryotic genomes (human, Drosophila melanogaster, Caenorhabditis elegans, the budding yeast Saccharomyces cerevisiae) is now known as the "RGS domain", an approximately 130 amino-acid domain that contacts the Gα switch regions to stabilize the transition state, thus accelerating GTP hydrolysis (i.e., RGS proteins act as GTPase-accelerating proteins or “GAPs” for Gα-GTP; e.g., ref.). Discovery of a superfamily of RGS domain-containing proteins that negatively regulate Gα-dependent signaling resolved a prior paradox that GPCR-stimulated signals are seen to terminate much faster in vivo than predicted from the slow GTP hydrolysis rates exhibited by purified Gα subunits in vitro. RGS proteins are now considered key desensitizers of heterotrimeric G protein signaling and, as such, as new drug discovery targets. This foundational work by Siderovski on a new class of GPCR signaling regulators has been cited over 18,000 times according to Google Scholar and also resulted in Siderovski editing a two-volume set of Methods in Enzymology chapters devoted to these regulatory proteins.

Characterization of RGS protein RGS2

The first Regulator of G protein Signaling that Siderovski cloned, RGS2, was subsequently found to be a potent GTPase-accelerating protein (GAP) for G-alpha-q in vitro and an attenuator of Gq-coupled receptor signaling in cell-based assays (e.g., ref.). The Siderovski group, in a long-standing collaboration with the Structural Genomics Consortium node in Oxford, UK, used x-ray crystallography and site-directed mutagenesis to ascertain the role of three critical residues within RGS2 that control its unique selectivity for G-alpha-q family subunits. To begin to ascertain the physiological function(s) of RGS2, Siderovski worked with Amgen Inc. colleagues to ablate the Rgs2 locus in mice. These knockout mice were critical to observing that Rgs2 loss-of-function mutations lead to constitutive hypertension. Other vascular phenotypes in RGS2-null mice were seen to include persistent vasoconstriction, renovasculature abnormalities, and prolonged response to vasoconstrictors; all of these mouse phenotypes are consistent with an increase in G-alpha-q signaling given the loss of RGS2 GAP activity. These mouse-based studies have helped inform subsequent studies of the human condition, in which genetic variations have now been identified in the human RGS2 gene between hypertensives and normotensives.

Discovery of the GoLoco motif

Using then-nascent techniques of bioinformatics and genome data-mining to uncover novel regulators of G-protein signaling, Siderovski discovered a unique, second Gα interaction site, the GoLoco motif, within RGS12 and RGS14 that is shared with a number of non-RGS-domain-containing proteins. The GoLoco/Gα interaction leads to inhibition of spontaneous nucleotide release – an activity previously thought to be the exclusive role of the Gβγ subunit. Siderovski's 2002 Nature paper established the structural determinants of GoLoco motif biochemical activity and binding selectivity by describing the first high-resolution structure of a GoLoco motif/Gα complex. The true value of this GoLoco motif discovery was fully realized in subsequent 2003 Science and 2004 Cell papers describing that GoLoco motif-containing proteins GPR-1 and GPR-2 are critical for asymmetric cell division in the Caenorhabditis elegans zygote. Those findings cemented the emerging view that GoLoco motif proteins act in a hitherto unexpected arena: namely, establishing a novel, receptor-independent Gα nucleotide cycle that controls microtubule dynamics, mitotic spindle pulling forces, and the act of chromosomal segregation during cell division. Clinical genetic studies of variants in the human gene encoding a related GoLoco motif protein, GPSM3, have more recently revealed important insights into the role of neutrophil migration during the initiating stages of rheumatoid arthritis development.

Discovery of the plant RGS protein AtRGS1

With the multitude of RGS proteins encoded within mouse, man, and model organisms, one central question has arisen: Is there any selectivity in their actions towards particular GPCRs? Dr. Siderovski's 2003 report of the cloning of AtRGS1, the first plant RGS protein identified (from the model organism Arabidopsis thaliana), gave an emphatic demonstration of functional linkage between an RGS domain and a particular GPCR. The AtRGS1 protein is a unique amalgam of the two: an N-terminus with the topology and transmembrane domains of a GPCR and a C-terminal intracytosolic RGS domain. The action of the AtRGS1 RGS domain opposes that of the activated plant Gα (AtGPA1) in increasing cell elongation in hypocotyls in darkness and increasing cell production in roots grown in light. The discovery of AtRGS1 and its action in plant cell proliferation cast new light on the potential actions of cognate constituents in mammalian GPCR signaling. The presence of both GEF-like (GPCR) and GAP-like (RGS) domains within AtRGS1 may seem paradoxical at first blush (i.e., a potential futile cycle of nucleotide exchange and hydrolysis); however, the prevailing hypothesis put forth by Dr. Siderovski and colleagues is that AtRGS1 represents a ligand-operated GAP, given that AtGPA1 exhibits the highest rate of spontaneous nucleotide exchange as well as the slowest intrinsic GTPase activity ever seen for a wildtype Gα subunit.

Characterization of RGS protein RGS21

With sponsored research funding (2007-2013) from The Coca-Cola Company on the molecular determinants of taste, Siderovski's group was the first to establish that RGS21, a small RGS protein whose mRNA transcript is uniquely expressed in taste bud cells, has promiscuous Galpha-directed GAP activity in vitro. A patent based on these studies was jointly published by the Siderovski group and staff of The Coca-Cola Company.

Contributions to medical education and scholarship

From 2006 to 2012, Siderovski was the Thomas J. Dark Basic Science Director of UNC's Medical Scientist Training Program and directly responsible for assisting MD/PhD combined-degree trainees through their progress to PhD completion. In August 2014, Siderovski was appointed Director of the West Virginia University School of Medicine MD/PhD Scholars Program. While Co-Director of the WVU Addictions Research Group, Siderovski has been active in leading WVU's educational, clinical, and research response to the opioid addiction crisis (e.g., ref.), including curation of a daily, West Virginia-centric blog (https://wvthdc.wordpress.com) on local events and responses to the crisis. In continued support of the highest standards of scientific discourse, Siderovski has been serving as Editorial Board Member for the Journal of Biological Chemistry since 2012.

Honors

In 2001, Siderovski was awarded a $210,000 New Investigator Award in the Pharmacological Sciences by the Burroughs Wellcome Fund. In 2004, Siderovski was named the top American Pharmacologist under 40 and awarded the John J. Abel Award by the American Society for Pharmacology and Experimental Therapeutics. In 2006, the University of North Carolina at Chapel Hill awarded Siderovski the Phillip and Ruth Hettleman Prize for Artistic and Scholarly Achievement for his research on regulators of G protein signaling. On June 22, 2012, the UNC Department of Pharmacology said farewell [1] to Siderovski upon his move to become the Chair of the Department of Physiology and Pharmacology at West Virginia University: "Our congratulations to David.  We wish him well in his new leadership position. We are better off for his having been here."

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