Dynamic responses to cell stress
Welcome to Jorrit Enserink's research group
Quick overview of the group
The Enserink group is a research group with people from five different countries, and currently consists of the group leader, one senior researcher, three post-docs, three PhD students and a varying number of undergraduate students.
Cells are continuously exposed to changes in their environment. For optimal growth and survival, cells have developed mechanisms that sense these alterations and generate responses that maintain cellular homeostasis. A major response to environmental stimuli is transcriptional reprogramming.
The lab’s main goal is to understand how cells cope with environmental changes, in particular in terms of regulation of transcription. We mainly focus on regulation of transcription by post-translational modifications, such as phosphorylation, ubiquitination and sumoylation. We make use of the model organism Saccharomyces cerevisiae as well as vertebrate cell lines.
1. Cancer research projects
Our cancer research projects are primarily focused on oncogene addiction. Oncogene addiction is the puzzling phenomenon in which cells which have been exposed to the activity of a specific oncogene for a certain period of time suddenly become critically dependent upon the continuous activity of that oncogene for their survival. In this process, the oncogene somehow re-wires cellular survival pathways. How this is accomplished is not well understood, although it has been suggested to involve irreversible alterations of transcriptional programs. We are particularly interested in unraveling the mechanisms by which these oncogenes re-wire the transcriptional circuitries of cells.
Development of novel cancer therapies
We are particularly interested in developing novel treatment options for rare forms of cancer, as well as for cancers that do not respond to current forms of therapy. One example is mast cell leukemia, a rare but extremely aggressive form of leukemia with little treatment options and dismal prognosis. Another example is drug-resistant chronic myeloid leukemia (CML), which can also be difficult to treat. Using methods originally developed for yeast research, we have designed a powerful cell competition assay that we are using for high-throughput screening of large drug libraries. The goal of these screens is to identify compounds that specifically kill oncogene-expressing cells while leaving isogenic, untransformed cells unharmed.
2. Basic research projects
Sumoylation and cell stress
We want to understand how cells modulate transcription in response to environmental changes, in particular nutrient starvation. We are particularly interested in the role of the ubiquitin family protein Sumo. Sumoylation is clearly important in rewiring of transcription in response to cell stress. However, which proteins are sumoylated and how Sumo regulates their function remains mysterious. By performing ChIP-seq experiments and mass spectrometry we have identified a number of proteins that become sumoylated during cell stress. We are currently studying the molecular mechanism by which Sumo modulates the activity of these proteins to regulate transcription.
Regulation of transcription by signal transduction kinases and phosphatases
Another major focus of the group is to determine how kinases and phosphatases regulate transcription. In response to specific environmental cues, signaling pathways rewire transcriptional programs to make sure the cell optimally responds to changes in conditions. These signaling pathways often consist of kinases and phosphatases. However, how these enzymes control transcription is not well understood. Using a combination of ChIP-seq, mass spectrometry and fluorescence microscopy we are unraveling the molecular mechanisms by which signaling kinases and phosphatases control transcription.
Rad6 in transcription and cell cycle regulation
Using a high-throughput chemical-genetic screen, we found that the E2 ubiquitin conjugase Rad6 is temporally recruited to promoter regions of cyclin genes, where it ubiquitinates histone H2B (Fig. 1). This promotes transcription of cyclins, thereby activating the cyclin dependent kinase Cdk1 to promote efficient cell cycle entry.
Cdk1 in regulation of transcription
We discovered that Cdk1 has a kinase-dependent function in regulation of the basal transcription machinery. Using ChIP-seq, we found that Cdk1 localizes to highly transcribed genes, primarily involved in housekeeping. At these genes, Cdk1 cooperates with another CDK, Kin28 (the catalytic subunit of TFIIH), to phosphorylate RNA polymerase II (Fig. 2). RNA polymerase II has a long C-terminal domain that consists of 28 repeats of the sequence Y1S2P3T4S5P6S7. Cdk1 and Kin28 promote phosphorylation of the serine residue at position 5 (Ser5). This in turn is important for efficient recruitment of the capping machinery, which places a cap on the mRNA as soon as it protrudes from the polymerase.
Figure 2. A model for cooperation between Cdk1 and Kin28 in regulation of RNA polymerase II. (A) Kin28 phosphorylates the C-terminal domain of RNA pol II, which may result in recruitment of Cdk1, which further phosphorylates RNA pol II (B).
Cell reponses to nutrient stress: Regulation of fatty acid and ceramide metabolism by TORC1 and GSK3
Very long chain fatty acids (VLCFAs) are essential fatty acids with multiple functions, including ceramide synthesis. Although the components of the VLCFA biosynthetic machinery have been elucidated, how their activity is regulated to meet the cell’s metabolic demand remains unknown. We recently found that the fatty acid elongase Elo2 is regulated by phosphorylation. Elo2 phosphorylation is induced by nutrient stress and inhibition of TORC1 and requires GSK3. We found that expression of nonphosphorylatable Elo2 profoundly altered the ceramide spectrum, which reflects aberrant VLCFA synthesis. Furthermore, depletion of VLCFAs resulted in constitutive activation of autophagy. This constitutive activation of autophagy diminished cell survival, indicating that VLCFAs serve to dampen the amplitude of autophagy. Together, our data revealed a function for TORC1 and GSK3 in the regulation of VLCFA synthesis with important implications for autophagy and cell homeostasis.
Institutions that finance our research
Research in the Enserink group, which includes salaries for all the lab members and the PI, is entirely financed by extramural grants from the Norwegian Research Council, The Norwegian Cancer Society and by the Norwegian Health Authority South-East.
Selected publications (for a complete list see here):
1. TORC1 Inhibits GSK3-Mediated Elo2 Phosphorylation to Regulate Very Long Chain Fatty Acid Synthesis and Autophagy. Zimmermann C, Santos A, Gable K, Epstein S, Gururaj C, Chymkowitch P, Pultz D, Rødkær SV, Clay L, Bjørås M, Barral Y, Chang A, Færgeman NJ, Dunn TM, Riezman H and Enserink JM. Cell Reports 2013 Nov 27;5(4):1036-46. Article prize from Oslo University Hospital.
2. Cdc28 kinase activity regulates the basal transcription machinery at a subset of genes. Chymkowitch P, Eldholm V, Lorenz S, Zimmermann C, Lindvall JM, Bjørås M, Meza-Zepeda L, Enserink JM*. Proc Natl Acad Sci U S A 2012 Jun 26;109(26):10450-5.
3. A chemical-genetic screen to unravel the genetic network of CDC28/CDK1 links ubiquitin and Rad6-Bre1 to cell cycle progression. Zimmermann C, Chymkowitch P, Eldholm V, Putnam CD, Lindvall JM, Omerzu M, Bjørås M, Kolodner RD, Enserink JM*. Proc Natl Acad Sci U S A 2011 Nov 15;108(46):18748-53.
4. What makes the engine hum: Rad6, a cell cycle supercharger. Enserink JM* and Kolodner RD. Cell Cycle 2012 Jan 15;11(2):249-52.
5. An overview of Cdk1-controlled targets and processes. Enserink JM*, Kolodner RD. Cell Div. 2010 May 13;5:11 (review).
6. The Saccharomyces cerevisiae Rad6 postreplication repair and Siz1/Srs2 homologous recombination-inhibiting pathways process DNA damage that arises in asf1 mutants. Kats ES, Enserink JM, Martinez S, Kolodner RD. Mol Cell Biol. 2009 Oct;29(19):5226-37.
7. Cdc28/Cdk1 positively and negatively affects genome stability in S. cerevisiae. Enserink JM, Hombauer H, Huang ME, Kolodner RD. J Cell Biol. 2009 May 4;185(3):423-37.
8. An FHA domain-mediated protein interaction network of Rad53 reveals its role in polarized cell growth. Smolka MB, Chen SH, Maddox PS, Enserink JM, Albuquerque CP, Wei XX, Desai A, Kolodner RD, Zhou H. J Cell Biol. 2006 Dec 4;175(5):743-53.
9. Checkpoint proteins control morphogenetic events during DNA replication stress in Saccharomyces cerevisiae. Enserink JM, Smolka MB, Zhou H, Kolodner RD. J Cell Biol. 2006 Dec 4;175(5):729-41.
10. The cAMP-Epac-Rap1 pathway regulates cell spreading and cell adhesion to laminin-5 through the alpha3beta1 integrin but not the alpha6beta4 integrin. Enserink JM, Price LS, Methi T, Mahic M, Sonnenberg A, Bos JL, Taskén K. J Biol Chem. 2004 Oct 22;279(43):44889-96.
11. Cyclic AMP induces integrin-mediated cell adhesion through Epac and Rap1 upon stimulation of the beta 2-adrenergic receptor. Rangarajan S#, Enserink JM#, Kuiperij HB, de Rooij J, Price LS, Schwede F, Bos JL. J Cell Biol. 2003 Feb 17;160(4):487-93.
12. A novel Epac-specific cAMP analogue demonstrates independent regulation of Rap1 and ERK. Enserink JM, Christensen AE, de Rooij J, van Triest M, Schwede F, Genieser HG, Døskeland SO, Blank JL, Bos JL. Nat Cell Biol. 2002 Nov;4(11):901-6.
Aug 19, 2014
Latest PubMed articles
The cell cycle rallies the transcription cycle: Cdc28/Cdk1 is a cell cycle-regulated transcriptional CDK
Transcription, 4 (1), 3-6
Chemical genetics: budding yeast as a platform for drug discovery and mapping of genetic pathways
Molecules, 17 (8), 9258-73