Professor, Cellular & Molecular Medicine; Cancer Biology Focus Leader
Ph.D., University of California, Irvine
Regulation of G1 Cell Cycle Progression in Cancer - Cell cycle progression from early G1 to late G1 and then into S phase requires both increased cellular growth, resulting in an accumulation of mass, and the concerted activities of multiple cyclin-dependent kinases (cdk), cdk inhibitors and tumor suppressors. The vast majority of malignant cells selectively target these pathways for alteration. Our lab is focused on determining the consequences of these genetic and epigenetic alterations and the mechanism that cell growth activates the cell cycle machinery. Recent work has shown that Rb is activated by mono-phosphorylation via cyclin D:cdk4/6 complexes and that cyclin E:Cdk2 complexes perform the inactivating hyper-phosphorylation of Rb at the Restriction Point. How cyclin E:Cdk2 becomes activated remains a mystery and is an extremely important question for understanding carcinogenesis as all tumors deregulate Restriction point control.
We are also interested in developing novel macromolecular delivery of RNAi therapeutics to induce synthetic lethal responses to treat cancer. Delivery across the cell membrane is restricted to uncharged, small molecules less than 500 Daltons in size. However, siRNAs are in vast excess to this bioavailability limitation and contain 40 anionic negative charges on the phosphate backbone. We set-up two nucliec acid chemistry labs and developed an entirely new field of bioreversible phosphotriester groups that neutralized the siRNA backbone, called siRNNs (RiboNucleic Neutrals). Once inside cells, intracellular thioesterases cleave off the phosphotriester groups on siRNNs to reveal a negatively charged phosphodiester backbone that is required for loading into Ago2 and induction of RNAi responses. We've delivered siRNNs into preclinical mouse models. Currently, we are developing Antibody-siRNN Conjugates (ARC) to target siRNNs to specific tumor types, including prostate cancer and AML, in mouse models.
e have focused a lot of our attention on delivery by protein transduction domains (PTDs)/cell penetrating peptides (CPPs), such as the TAT peptide. Our recent work has uncovered the mechanism that these peptides enter cells, namely macropinocytosis, a specialized form of fluid phase endocytosis, and devised methods to enhance endosomal escape. In addition, we have a nucleic acid chemistry group in my lab that has synthesized an entirely new class of siRNAs that we are beginning to test biologically in vitro and in vivo in metastatic models of ovarian cancer.
BMS Focus Areas:
Kaulich, M., Lee, Y.J., Lonn, P., Springer, A.D., Meade, B.R., & Dowdy, S.F. Efficient CRISPR-AAV Engineering of Endogenous Genes to Study Protein Function. Nucleic Acids Research. doi: 10.1093/nar/gku1403 (2015).
Meade, B.R., Gogoi, K., Hamil, A.S., Palm-Apergi,C., van den Berg, A., Hagopian, J.C., Springer, A.D., Eguchi, A., Kacsinta, A.D., Dowdy, C.F., Presente, A., Lönn, P., Kaulich, M., Yoshioka, N., Gros, E., Cui, X.-S. & Dowdy, S.F. Efficient delivery of RNAi prodrugs containing reversible charge-neutralizing phosphotriester backbone modifications. Nature Biotechnology 32:1256-1261 (2014).
Narasimha, A.M., Kaulich, M., Shapiro, G.S., Choi, Y.J., Sicinski, P. & Dowdy, S.F. Cyclin D Activates the Rb Tumor Suppressor by Mono-Phosphorylation. eLife doi: 10.7554/eLife.02872 (2014).
Yoshioka, N., Gros, E., Li, H.-R., Kumar, S., Deacon, D.C., Maron, C., Muotri, A.R., Chi, N.C., Fu, X.-D., Yu, B.D. & Dowdy, S.F. Efficient Generation of Human iPS Cells by a Synthetic Self-Replicative RNA. Cell Stem Cell 13:246-254 (2013).