We apply genetics and cell biology approaches to understand and improve drug therapy; we are also interested in the elucidation of the function of pseudo-enzymes.
High-throughput screens to understand and improve lung inflammation therapies
Asthma is a major chronic lung inflammation disease that affects over 300 million people worldwide. The combination of beta-2 adrenergic receptor (B2AR) agonists and glucocorticoid receptor (GR) ligands is a mainstay in asthma therapy, but has some limitations and severe side effects, including desensitization and resistance. We design cell based assays, and then perform high-throughput screens to identify genes involved in the regulation of asthma drugs. Elucidation of the underlying mechanisms of those genes would provide insights into rational drug discovery.
We have developed a novel EST-derived shRNA library that targets both coding and non-coding regions of human genome. A genome wide screen with the library led to the identification of a large number of regulatory genes involved in agonist induced B2AR down-regulation. In particular, we identified farnesyl diphosphate synthase, the target of a FDA approved drug alendronate, and uncovered that the enzyme controls agonist induced B2AR down-regulation through modulating the membrane localization of small GTPases and B2AR internalization. Importantly, alendronate reverses beta-2 agonist desensitization in both biochemical and functional assays. Therefore, our findings reveal the potential of alenodronate in the improvement of beta-2 agonist therapy.
We have also carried out a high-throughput chemical screen for small molecular modulators of glucocorticoid receptor. We have screened 600 drugs and 8000 bioactive compounds, and identified several intense GR inhibitors and activators, including kinase inhibitors and DNA interacting compounds. We have validated those hits, and are currently characterizing the biochemical mechanisms underlying their effects on GR. The combination of those hits and GR ligand drugs are also being tested to estimate whether the hits modulate inflammation suppression of drugs.
Pharmacogenomic studies of asthma drugs
In collaboration with Dr. Scott Weiss’ group at Harvard Medical School, we utilize GWAS (Genome-wide association analysis) and RNA-Seq approaches on clinical asthma patients samples, and determine drug response genes. We found the first drug sensitivity SNP in asthma and further validated that the associated gene controls B2AR expression. We have also identified a secreted protein gene that is strongly response to GR ligand drugs and regulates inflammation.
Explore the function of pseudo-enzymes
Pseudo-enzymes lack catalytic activity, but are often well expressed and conserved, implying they may have some biological functions. We have identified a unique pseudo-enzyme that is composed of an inactive ubiquitin E2 conjugating enzyme domain and an inactive glucose metabolism enzyme domain. We are taking various approaches including CRISPR, genomics, proteomics, metabolomics and genetically engineered mouse to explore the function of the enzyme, particularly in protein degradation and cancer metabolism.
1. Jiang X., Pan H., Nabhan J.F., Krishnan R., Koziol-White C., Panettieri R.A., Lu Q. (2012) A novel EST-derived RNAi screen reveals a critical role for farnesyl diphosphate synthase in beta-2 adrenergic receptor internalization and down-regulation. FASEB J. 26(5):1995-2007.
2. Himes B.E., Jiang X., Hu R., Wu A.C., Lasky-Su J.A., et al. (2012) Genome-wide association analysis in asthma subjects identifies SPATS2L as a novel bronchodilator response gene. PLoS Genet. 8(7):e1002824.
3. Jiang X., Xu Y., Price B.D. (2010) Acetylation of H2AX on lysine 36 plays a key role in the DNA double-strand break repair pathway. FEBS Lett. 584(13):2926-2930.
4. Xu Y., Sun Y., Jiang X., Ayrapetov M.K., Moskwa P., Yang S., Weinstock D.M., Price B.D. (2010) The p400 ATPase regulates nucleosome stability and chromatin ubiquitination during DNA repair. J. Cell Biol. 191(1):31-43.
5. Sun Y., Jiang X., Xu Y., Ayrapetov M.A., Moreau L.A., Whetstine J.R. and Price B.D. (2009) Histone H3 methylation links DNA damage detection to activation of the Tip60 tumor suppressor. Nat. Cell Biol. 11(11):1376-1382.
6. Jiang X., Sun Y., Chen S., Roy K. and Price B.D. (2006) The FATC domains of the PIKK proteins are functionally equivalent and participate in the Tip60 dependent activation of DNA-PKcs and ATM. J. Biol. Chem. 281(23): 15741-15746.
7. Sun Y., Jiang X., Chen S., Fernandes N. and Price B.D. (2005) A role for the Tip60 histone acetyltransferase in the acetylation and activation of ATM. Proc. Natl. Acad. Sci. U.S.A. 102(37): 13182- 13187.