Ph.D., The Hahnemann Medical College
B.S., Union College
Office Phone: (405) 271-2377
Fax Number: (405) 271-3548
University of Oklahoma Health Sciences Center
Department of Cell Biology
940 Stanton L.Young Blvd., BMS 564
Oklahoma City, OK 73104
Our laboratory has focused upon the mechanism of transcription by RNA polymerase I and its regulation. It has long been our hypothesis that understanding the mechanism of transcription would 1) provide the basis for understanding its regulation and 2) provide a mechanism for its inhibition under conditions where it is dysregulated or pathological.
1. The laboratory's first studies focused on the definition of the cis-acting elements and trans-acting factors of rDNA transcription and focused on the rat rDNA repeat. These studies contributed to our understanding of the mechanism of transcription of the mammalian ribosomal genes. We found that the promoter consisted of two domains a core promoter element required for transcription and an upstream element required for stable preinitiation complex formation (a) and that they must be stereochemically aligned (b). Subsequently we demonstrated that rat rDNA transcription required three components in vitro, competent RNA polymerase I, a species specific transcription factor (similar to human SL1) and a factor that increased the efficiency of transcription, similar to human UBF (c), and that UBF was not species specific (d) in contrast to other reports.
a. Xie, W.Q., Rothblum, L.I. Domains of the rat rDNA promoter must be aligned stereospecifically. Mol Cell Biol. 1992 Mar;12(3):1266-75. PMID: 1545808 PMCID: PMC369559
b. Cassidy, B., Haglund, R., Rothblum, L.I. Regions upstream from the core promoter of the rat ribosomal gene are required for the formation of a stable transcription initiation complex by RNA polymerase I in vitro. Biochim Biophys Acta. 1987 Jul 14;909(2):133-44. PMID: 3593729
c. Smith, S.D., Oriahi, E., Lowe, D., Yang-Yen, H.F., O'Mahony, D., Rose, K., Chen, C., and Rothblum, L.I. Characterization of factors that direct transcription of rat ribosomal DNA. Mol. Cell. Biol. 10: 3105-3116, 1990. PMID: 2342470 PMCID: PMC360675
d. Pikaard, C.S., Smith, S.D., Reeder, R.H., Rothblum. L. rUBF, an RNA polymerase I transcription factor from rats, produces DNase I footprints identical to those produced by xUBF, its homolog from frogs. Mol Cell Biol. 1990 Jul;10(7):3810-2. PMID:2355924 PMCID:PMC360842
2. Our understanding of the role(s) of one of the transcription factors, UBF, led to two important discoveries. First, in collaboration with Howard Morgan and Bruce Sells we demonstrated that rDNA transcription was the central mechanism through which the accumulation of ribosomes was regulated in hypertrophic growth (a) and development (b). This was contrary to dogma and established new paradigms for understanding both mitotic and hypertrophic growth. Secondly, we found that the protein product of the retinoblastoma susceptibility gene, Rb, a known anti-oncogene and regulator of transcription by RNA polymerase II also regulated transcription by RNA polymerase I. Again, this was a paradigm shift and has led to a greater understanding of how cells regulate transcription by all three nuclear transcription systems (c,d).
a. McDermott, P.J., Rothblum, L.I., Smith, S.D., Morgan, H.E.: Accelerated rates of ribosomal RNA synthesis during growth of contracting heart cells in culture. J. Biol. Chem., 264:18220-18227, 1989. PMID: 2808374
b. Larson DE, Xie W, Glibetic M, O'Mahony D, Sells BH, Rothblum LI. Coordinated decreases in rRNA gene transcription factors and rRNA synthesis during muscle cell differentiation. Proc Natl Acad Sci U S A. 1993 Sep 1;90(17):7933-6. PMID: 8396256 PMCID: PMC47261
c. Cavanaugh, A.H., Hempel, W. M., Taylor, L.J., Rogalsky, V., Todorov, G., Rothblum, L.I. Activity of RNA polymerase I transcription factor UBF blocked by Rb gene product. Nature, 374: 177-180, 1995. PMID: 7877691
d. Hannan, K.M., Hannan, R.D., Smith, S.D., Jefferson,L.S., Lun, M., Rothblum, L.I. Rb and p130 regulate RNA polymerase I transcription: Rb disrupts the interaction between UBF and SL-1. Oncogene. 19:4988-4999, 2000. PMID: 11042686
3. Our most recent work has focused on the role of a polymerase associated initiation factor, Rrn3 in rDNA transcription, its function and its regulation. We were the first to demonstrate that this was the rDNA transcription factor first identified by Fu Li-Yu and Feigelson that was cycleheximide sensitive. We showed that cycloheximide inhibited its phosphorylation and its association with Pol I (a), and that it must be phosphorylated to function in recruitment of the polymerase to the committed template. We demonstrated that Rrn3 functioned stoichiometrically and not catalytically (b), that it was required for the formation of the heparin-resistant open promoter complex (c) and that it itself was a DNA-binding protein (d).
In the course of studying the assembly of Rrn3 with Pol I, we focused on the interaction between Rrn3 and Pol I which is mediated by rpa43. We found that a 22 amino acid peptide from rpa43 was necessary and sufficient for this interaction. Moreover, we found that adding this peptide to an in vitro transcription reaction inhibited rDNA transcription. When we transduced the peptide into cells in culture, we found that it inhibited rDNA transcription, just as it had in vitro (e). Moreover, the inhibition of rDNA transcription led to the death of tumor cells of different origins within 48 hours. In contrast, the peptide reversibly inhibited the proliferation of "normal" tissue culture cells, but did not cause cell death. The relationship between the inhibition of rDNA transcription, or ribosome biogenesis, and cell death, apoptotic or otherwise, has been noted by others and is said to be caused by "nucleolar stress". Our future studies are designed to elucidate the nature of the interaction between Rrn3 and rpa43 so that we can derive the structure of a pharmacophore to facilitate the development of a drug, peptide or otherwise, that will target rDNA transcription in tumor cells.
a. Cavanaugh, A.H., Hirschler-Laszkiewicz, I., Hu, Q., Dundr, M., Smink, T., Misteli, T., Rothblum, L.I. Rrn3 phosphorylation is a regulatory checkpoint for ribosome biogenesis. J. Biol. Chem. 277: 27423-27432, 2002. PMID: 12015311
b. Hirschler-Laszkiewicz, I., Cavanaugh, A., Mirza, A., Lun, M., Hu, Q., Smink, T., Rothblum, L.I. Rrn3 becomes inactivated in the process of ribosomal DNA transcription.. J. Biol. Chem. 278: 18953–18959, 2003. PMID: 12646563
c. Cavanaugh, A. H., Evans, A. Rothblum, L.I. Mammalian Rrn3 Is Required for the formation of a Transcription Competent Preinitiation Complex Containing RNA Polymerase I. Gene Expression. 14:131-147, 2008. PMID: 18590050 PMCID: PMC2526047
d. Stepanchick, A. Zhi, H-J., Cavanaugh, A., Rothblum, K., Schneider, D.A., Rothblum, L.I. DNA-binding by the ribosomal DNA transcription factor Rrn3 is essential for ribosomal DNA Transcription. J Biol Chem.; 288:9135-44, 2013 PMID: 23393135 PMCID: PMC3610986
e. Rothblum, K., Hu, Q., Penrod, Y., Rothblum L.I. Selective Inhibition of rDNA Transcription by a Small-Molecule Peptide that Targets the Interface Between RNA Polymerase I and Rrn3. Mol Cancer Res. 12:1586-1596.2014 PMID: 25033839 PMCID: PMC4233170
Cavanaugh AH, Hempel WM, Taylor LJ, Rogalsky V, Todorov G, and Rothblum LI. Activity of rNA polymerase I transcription factor UBF blocked by Rb gene product. Nature, 374:177-180. 1995.
Hannan RD, Luyken J, and Rothblum LI. Regulation of rDNA transcription factors during cardiomyocyte hypertrophy induced by adrenergic agents. J. Biol. Chem. 270:8290-8297. 1995.
Hannan K, Kennedy BK, Cavanaugh A, Hannan RD, Hirschler-Laszkiewicz I, Jefferson L, Rothblum LI. RNA polymerase I transcription in Confluent Cells: Rb downregulates rDNA transcription during confluence-induced cell cycle arrest. Oncogene. 19:3487-3497, 2000.
Cavanaugh AH, Hirschler-Laszkiewicz I, Hu Q, Dundr M, Smink T, Misteli T, and Rothblum LI. Rrn3 phosphorylation is a regulatory checkpoint for ribosome biogenesis. J. Biol. Chem. 277:27423-27432, 2002.
Dundr M, Hoffmann-Rohrer U, Hu Q, Grummt I, Rothblum LI, Phair RD, Misteli T. A kinetic framework for a mammalian RNA polymerase in vivo. Science, 298:1623-626, 2002.
Hirschler-Laszkiewicz I, Cavanaugh A, Mirza A, Lun M, Hu Q, Smink T, and Rothblum LI. Rrn3 functions stoichiometrically in ribosomal DNA transcription. J. Biol. Chem. 278:18953-18959, 2003.
Brandenburger Y, Arthur JF, Woodcock EA, Du, X-J, Gao, X-M, Autelitano, DJ, Rothblum, LI, and Hannan RD. Cardiac hypertrophy in vivo is associated with increased expression of the ribosomal gene transcription factor UBF. FEBS Letters 548:79-84, 2003.
Stefanovsky V, Langlois F, Gagnon-Kugler T, Rothblum LI, and Moss T. Growth factor signaling regulates elongation of RNA polymerase I transcription in mammals via UBF phosphorylation and r-chromatin remodeling. Mol. Cell. 21:629-639, 2006.
Cavanaugh AH, Evans A, Rothblum LI. Mammalian Rrn3 is required for the formation of a transcription competent preinitiation complex containing RNA polymerase I. Gene Expr. 14:131-147, 2008.
Sanij E, Poortinga G, Sharkey K, Hung S, Holloway TP, Quin J, Robb E, Wong LH, Thomas WG, Stefanovsky V, Moss T, Rothblum L, Hannan KM, McArthur GA, Pearson RB, Hannan RD. UBF levels determine the number of active ribosomal RNA genes in mammals. J Cell Biol. 183:1259-1274, 2008.
Penrod Y, Rothblum K, Rothblum LI. (2012) Characterization of the interactions of mammalian RNA polymerase I associated proteins PAF53 and PAF49. Biochemistry 51:6519-6526.
Hannan KM, Sanij E, Rothblum LI, Hannan RD, Pearson RB.(2013) Dysregulation of RNA polymerase I transcription during disease. Biochim Biophys Acta. 1829(3-4):342-360.
Stepanchick A, Zhi H, Cavanaugh AH, Rothblum K, Schneider DA, Rothblum LI. (2013) DNA binding by the ribosomal DNA transcription factor Rrn3 is essential for ribosomal DNA transcription. J Biol Chem. 288:9135-9144.
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Profile Last Updated: Feb. 26, 2018