Selective Regulation of Akt2 by Oxidation
Protein kinase B/Akt is a major signaling hub in cytokine, growth factor and integrin signaling pathways of consequence to many biological processes.
In mammals, three isoforms of Akt — Akt1/PKBα, Akt2/PKBβ and Akt3/PKBγ — regulate protein metabolism, cell proliferation, energy storage and apoptosis. Despite their high sequence identity, mouse knockout models lacking Akt isoforms have revealed extensive differences in the isoform phenotypes:
- Akt1 is involved in anabolic metabolism and regulation of apoptosis
- Akt2 is instrumental in the signaling of glucose metabolism
- Akt3 is implicated in neurological function and development
In general, these functional differences are attributed to variations in their tissue expression, temporal activation, subcellular location and substrate-specific signaling.
Furdui's lab discovered the first posttranslational modification that distinguishes between the Akt isoforms and demonstrated the isoform-specific oxidation of Akt2 at Cys124. Cys124 is situated in the linker region connecting the pleckstrin homology (PH) domain to the catalytic kinase domain of Akt2 and is not conserved in the other Akt isoforms.
The results are reported in two articles published in Proceedings of the National Academy of Sciences and Cell Cycle in 2011. The work was named by F1000 as among the "top 2 percent of published articles in biology and medicine."
Current research is aimed at determining structural changes induced by disulfide bond formation in Akt2, the mechanism that drives the formation and order of disulfides, and the consequence of oxidation on Akt2 trafficking within the cell. The group is also investigating the contribution of oxidized Akt2 to pathological conditions such as breast cancer progression and metastasis, radiation-associated diabetes, and impaired muscle function associated with aging.
Dissecting the Mechanisms of Peroxiredoxins Activity and Repair
Peroxiredoxins (Prxs) are ubiquitous, highly expressed antioxidant enzymes (up to 1 percent of cellular protein content) that can convert H2O2 and lipid peroxides (ROOH) to water and alcohol with high efficiency (rate constants ~107 M-1s-1). The function of Prxs is thought to be primarily protective in nature, and a number of studies have linked high Prx levels with the cancer phenotype, radiation resistance and response to chemotherapy.
Human cells contain six Prx isoforms with differences in subcellular localization and the content of Cys residues. The typical 2-Cys subclass (human Prx1–4) contains two active site Cys residues on each monomer of an obligate homodimer. Under high ROS, the active site cysteines can undergo hyperoxidation to -SO2H resulting in enzyme inactivation. The ATP-dependent enzyme sulfiredoxin (Srx) repairs this modification and facilitates re-entry of this species into the catalytic cycle. Furdui’s team collaborates closely with the laboratories of Dr. W. Todd Lowther and Dr. Leslie B. Poole to elucidate the catalytic steps in the mechanism of action as well as the repair of hyperoxidized Prx by Srx.