In our group, research focusses on the establishment of new test systems and new concepts for the development of antirheumatic drugs. For that purpose, various techniques like mammalian cell culture, protein purification and various molecular biology methods are employed to characterize the enzymes involved in inflammatory reactions. We work on the physiology and pharmacology of 5-lipoxygenase, an enzyme which is involved in host defence reactions. There are several main projects at the moment

1. Regulation of 5-lipoxygenase mRNA and protein expression
2. Regulation of cellular 5-lipoxygenase activity
3. Regulation of gene expression under inflammatory conditions, role of vitamin D receptor and RORalpha receptor.

5-Lipoxygenase catalyzes the transformation of arachidonic acid to leukotriene A4. This unstable intermediate can be converted to leukotriene B4 by LTA4-hydrolase or to leukotriene C4 by LTC4-synthase. Leukotrienes are involved in host defence reactions and play an important role in inflammatory diseases like asthma, psoriasis, inflammatory bowel disease and arthritis. The capability to release leukotrienes is restricted to a few cell types. Under pathophysiological conditions, leukotrienes are released from granulocytes, mast cells or macrophages. During hematopoiesis the competence of these cells for leukotriene biosynthesis is upregulated.
In mature cells, 5-LO activity is tightly regulated and seems to be under the control of additional cellular components. One cellular component, a membrane bound peptide termed FLAP which is necessary for 5-lipoxygenase activity in intact cells has been recently identified. Inhibitors of FLAP function prevent translocation of 5-lipoxygenase from cytosol to the membrane and inhibit 5-LO activation. Thus, the understanding of the regulatory mechanisms of cellular leukotriene biosynthesis provides new concepts for the development of antiinflammatory drugs.
An experimental approach to study the mechanisms involved in the regulation of leukotriene biosynthesis were investigations on the development of 5-LO expression and activity during myeloid cell maturation since it was well known that leukocytes develop 5-LO activity during cell differentiation. Therefore, in vitro differentiation of the human leukemic cell lines HL-60 and Mono Mac 6 was used as a model for granulocytic and monocytic cell maturation, respectively. The discovery, that the upregulation of the 5-lipoxygenase pathway was serum dependent finally lead to the identification of 1,25-dihydroxyvitamin D3 and transforming growth factor-beta (TGFß) as inducers of 5-lipoxygenase activity and enzyme expression.

Recently, we could demonstrate that the effects of 1,25-dihydroxyvitamin D3 and transforming growth factor-beta (TGFß) on 5-LO mRNA expression mainly depend on posttranscriptional events like the stimulation of transcript elongation and maturation whereas 5-LO promoter activity seems to be regulated by DNA methylation.

Depending on the cell growth conditions during cell maturation, strong discrepances between 5-lipoxygenase activity and enzyme expression were observed which lead to the characterization of the signal transduction cascades involved in the regulation of cellular 5-lipoxygenase activity.


Ongoing research projects:
 

1. Investigation of posttranslational modifications of RORalpha.
2. Investigation of the signal transduction cascades involved in 5-lipoxygenase activation.
3. Studies on the mechanism of induction of 5-lipoxygenase mRNA by 1,25-dihydroxyvitamin D3 and TGFß.
   The aim of the study is to elucidate whether induction of 5-lipoxygenase is mainly due to enhanced gene transcription or to posttranscriptional events.
4. Mechanistic studies of 5-lipoxygenase inhibition by various antiinflammatory drugs.

Support
Research of the group is supported by grants from the Deutsche Forschungsgemeinschaft (GRK 1172 and GRK 757/3) and by the EU (5th and 6th Framework Programme). The Research Training Group 1172 has been established in 2005 and focuses on the ‘Research, development and safety of biologicals'. This group is a partner in the FP6 Integrated Project EICOSANOX "Eicosanoids and Nitric Oxide: Mediators of Cardiovascular, Cerebral & Neoplastic Diseases". Furthermore, the group is a member of the DFG Research Unit "Signalling by Fatty Acid Metabolites and Sphingolipids"

geändert am 06. Mai 2008  E-Mail: Webmastersteinhilber@em.uni-frankfurt.de