The D4-GDI protein is a negative regulator of the Ras-related Rho family of small molecule "molecular switch" GTPases. The Rho GTPases modify cell structure and architecture via rapid changes to the actin cytoskeleton and cell membrane. Many of these physiological processes are associated with apoptotic cell death, thus the in vivo removal of D4-GDI inhibitory block is critical for proper induction and progression of apoptosis in cells. This removal of D4-GDI is effected by the caspase-3 protease, which cleaves the full length 28kD mature D4-GDI form into smaller 23kD and 5kD fragments. The 23kD fragment then translocates to the nucleus. Creighton University researchers used the D4-GDI antibody in their studies on human estrogen receptor-alpha (hER-alpha66) signaling in breast cancer models (1). They undertook this work in hopes of understanding estrogen and antiestrogen signaling networks and applying this knowledge to explain why some cancers are resistant to anti-estrogen therapy and therefore improve future design of treatment strategies for patients. A paper from Okamoto's lab employed the D4-GDI antibody to allow them to dissect apoptotic pathways in thymic cells that were subjected to ionizing radiation and UV light (2). These investigators were interested in the differential regulation of caspase 9 in both of these scenarios, and identified a novel response mechanism that was agent types-specific. Further studies will focus on characterizing the DNA lesion complexes formed and what downstream pathways are activated by them. Brown et al relied upon the D4-GDI antibody for their studies on dengue virus infections in mast cells (3). This disease is due to an aberrant immune response, and these researchers investigated the role of antibody enhancement and apoptosis induction in the infection process.
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