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Curt Wittenberg, Ph.D.

Professor
Department of Molecular Medicine
California Campus
Laboratory Website
Scripps VIVO Scientific Profile
curtw@scripps.edu
(858) 784-9628

Research Focus

Control of Cell Cycle Initiation.  Progress through the eukaryotic cell cycle is driven by sequential waves of accumulation of regulatory proteins that determine the sequence of cell cycle events (Wittenberg and Reed, 2005). Our laboratory studies the regulation of G1/S transcription (sometimes called G1-specific transcription), the wave of expression of several hundred genes that is associated with commitment to a new cell cycle. Those genes are expressed under the control of two distinct transcription factors known as SBF and MBF. We have identified two transcriptional repressors that regulate the G1/S transcription factors. Whi5 specifically associates with and represses SBF-dependent transcription during early G1 phase (de Bruin et al., 2004). It is inactivated as a consequence of phosphorylation by the G1 cyclin/CDK complex, Cln3/Cdc28 leading to SBF activation. The second repressor, Nrm1, acts as a corepressor together with MBF to repress transcription as cells exit G1 phase (de Bruin et al., 2006) that is encoded by an MBF target and, thereby, participates in a negative feedback loop that limits G1-specific transcription.  Nrm1 is also antagonized by the Rad53 checkpoint kinase in cells responding to DNA replication stress (Travesa et al, 2012). Whi5 and Nrm1 share a small domain called the GTB motif that mediates their repressive interaction with their cognate transcription factor (Travesa et al, 2013).  The repression they impose is central to the architecture of G1/S regulatory circuitry. A similar wave of gene expression encoding many orthologous proteins occurs during G1 phase in metazoans, including humans, and is controlled by the E2F family of transcription factors. Deregulation of the Rb/E2F transcriptional circuit is tightly associated with disease including cancer. 

Role of the SCFGrr1 E3 Ubiquitin Ligase in Nutrient Uptake and Cell Proliferation.  The role of ubiquitylation is pervasive in biological regulatory mechanisms and defects in that process are associated with numerous human diseases.  Ubiquitylation is mediated by an enzymatic cascade that, like ubiquitin itself, is highly conserved throughout eukaryotes. One of the primary determinants of specificity of ubiquitylation occurs at the level of substrate selection which is mediated by the E3 component of the cascade, the ubiquitin ligase. The family of ubiquitin ligases is large and diverse.  Among E3 ligases, the SCF (Skp1-Cullin-F-box protein) family is the largest. Our laboratory has studied the SCFGrr1 E3 ubiquitin ligase, a critical element of both nutritional regulation of cell growth (Spielewoy et al, 2004; 2010) and cell cycle control (Lanker et al, 1995; Hsiung et al, 2001) targeting both transcriptional regulators and cyclin proteins for ubiquitylation and degradation. We have undertaken a detailed investigation of the nature of substrate selection and discrimination by the SCFGrr1 E3 ubiquitin ligase (Lanker et al, 1995; Hsiung et al, 2001; Berset et al, 2002; Spielewoy et al, 2004). Elucidation of the mechanisms by which E3 ubiquitin ligases, in general, and LRR-containing F-box proteins, specifically, recognize and regulate protein stability is of critical importance for the development of treatments via drug targeting and other approaches. 

Ribosome Biogenesis in Yeast  (In collaboration with Jamie Williamson, TSRI).  The eukaryotic ribosome biogenesis pathway involves the coordinated high level expression ~100 ribosomal protein (RP) genes, hundreds of ribosome biogenesis factor (RiBi) genes, as well as the multicopy ribosomal RNA (rRNA) genes. While a great deal is known about the inventory of RiBis, and the role of several of these in specific steps in biogenesis, there is a tremendous amount that remains to be discovered about the mechanism of binding of ribosomal proteins, and about the specific roles of RiBis. We have recently initiated studies to provide a better understanding of pathways for ribosomal protein association during biogenesis and the connection of those pathways to cell growth and proliferation.  One of our main approaches is to utilize stable isotope pulse labeling and quantitative mass spectrometry (QMS) to probe the dynamics of RPs and intermediates in ribosome biogenesis. QMS provides the opportunity to identify the protein composition in each of the intermediate pools, and the rate of synthesis can be derived from the rate of labeling.  Information about the role of RPs and RiBis can be obtained by perturbing the pathway, and observing the resulting changes in the metabolic pools. 

Education

Ph.D., Biology, University of California, Santa Barbara, 1983

Professional Experience

Postdoctoral Fellow: Steven I. Reed, Ph.D. University of California and The Scripps Research Institute, 1984-1988

Awards & Professional Activities

Fellow, American Association for the Advancement of Science, Appointed 2009

Selected References

All Publications

Travesa, A., Kalashnikova, T.I., de Bruin, R.A.M., Cass, S.R., Chahwan, C., Lee, D.E., Lowndes, N., and Wittenberg, C. (2013) Repression of G1/S transcription is mediated via interaction of the GTB motif of Nrm1 and Whi5 with Swi6. Mol. Cell. Biol. In press.

Travesa, A., Kuo, D., de Bruin, R.A.M., Kalashnikova, T.I., Guaderrama, M., Thai, K., Aslanian, A., Smolka, M.B., Yates, J.R., Ideker, T., and Wittenberg, C. (2012) DNA replication stress differentially regulates G1/S genes via Rad53-dependent inactivation of Nrm1. EMBO J 31, 1811–1822.

Spielewoy, N., Guaderrama, M., Wohlschlegel, J.A., Ashe, M., Yates, J.R., and C. Wittenberg. (2010) Npr2, yeast homolog of the human tumor suppressor NPRL2, is a target of Grr1 required for adaptation to growth under suboptimal nutrient conditions. Eukaryotic Cell 9, 592–601.

de Bruin, R., Kalashnikova, T.I., Aslanian, A., Wohlschlegel, J.A., Chawan, C., Yates, J., 3rd, Russell, P., and Wittenberg, C. (2008) DNA replication checkpoint promotes G1/S-specific transcription via Cds1-dependent phosphorylation of the MBF-bound repressor, Nrm1. Proc. Natl. Acad. Sci. USA 105, 11230-11235.

de Bruin, R., Kalashnikova, T.I., Chawan, C., McDonald, W.H., Wohlschlegel, J.A., Yates, J., 3rd, Russell, P., and Wittenberg, C. (2006) Constraining G1-specific transcription to late G1-phase:  The MBF-associated corepressor Nrm1 acts via negative feedback. Molecular Cell 23, 483-496.

Wittenberg, C., and Reed, S.I. (2005). Cell cycle-dependent transcription in yeast: promoters, transcription factors, and transcriptomes. Oncogene 24, 2746–2755.

Spielewoy, N., Flick, K., Kalashnikova, T.I., Walker, J.R., and Wittenberg, C.  (2004) Regulation and recognition of SCFGrr1 targets in the glucose and amino acid signaling pathways. Mol. Cell. Biol. 24, 8994–9005.

de Bruin, R., McDonald, W.H., Kalashnikova, T.I., Yates, J., 3rd, and C. Wittenberg (2004) Cln3 Activates G1-specific Transcription by Promoting Dissociation of the SBF-Bound Repressor, Whi5. Cell 117, 887-898.

Berset, C., Griac, P., Tempel, R., La Rue, J., Wittenberg, C., and Lanker, S. (2002). Transferable domain in the G(1) cyclin Cln2 sufficient to switch degradation of Sic1 from the E3 ubiquitin ligase SCF(Cdc4) to SCF(Grr1). Mol Cell Biol 22, 4463–4476. 

Hsiung, Y.G., Chang, H.C., Pellequer, J.L., La Valle, R., Lanker, S., and Wittenberg, C. (2001). F-box protein Grr1 interacts with phosphorylated targets via the cationic surface of its leucine-rich repeat. Mol Cell Biol 21, 2506–2520.

Lanker, S., Valdivieso, M.H., and Wittenberg, C. (1996). Rapid Degradation of the G1 Cyclin Cln2 Induced by CDK-Dependent Phosphorylation. Science 271, 1597–1601.