| Dab2IP (DOC-2/DAB2 interacting protein) is a novel member of the Ras GTPase-activating protein (Ras GAP) family which was previously identified by virtue of its interaction with Disabled-1 and -2 family proteins (Wang et al., 2002; Homayouni et al., 2003). In addition to its catalytic domain, Dab2IP contains several distinct domains for protein-protein and protein-lipid interactions, suggesting that Dab2IP is involved in cellular signaling. However, to date, its signaling mechanism is poorly understood. In addition, whereas Dab2IP is predominantly expressed in the brain (Chen et al., 2006), its spatio-temporal expression pattern and physiological role in the brain have not been explored.; In this study, a novel splice variant form of Dab2IP, called Dab2IP-L, was isolated and characterized. Dab2IP-L (GenBank accession number, DQ473307) encodes a longer pleckstrin homology (PH) domain than previously reported Dab2IP isoforms. The PH domain of Dab2IP-L preferentially binds to PtdIns(3,4,5)P 3 compared to PtdIns(4,5)P2. In addition, Dab2IP-L PH domain is involved in intramolecular interaction which is disrupted in the presence of PtdIns(3,4,5)P3. Notably, Dab2IP-L exhibits a Rap GTPase-activating protein (GAP) activity. In HEK 293T cells, overexpression of Dab2IP-L induced drastic cell rounding and cell detachment. A Dab2IP-L mutant lacking the PH domain failed in both inhibition of Rap activity and Dab2IP-L-mediated cell detachment, indicating that the PH domain plays a critical role in the cellular functions of Dab2IP-L.; In order to study the function of Dab2IP in brain development, Dab2IP-null mice were generated using a gene-trap strategy. Dab2IP was highly expressed in various brain regions including cerebellum, hippocampus, and neocortex. Interestingly, Dab2IP expression appeared to be transient and significantly reduced by post natal day 30 (P30) in the brain, especially in the cerebellum. Although the cerebellar morphology looked grossly normal in Dab2IP-null mice, immunohistological experiments revealed that Dab2IP-/- Purkinje cells receive significantly more climbing fiber (CF) contacts than their wild-type litermates. Furthermore, in contrast to wild-type Purkinje cells, the characteristic CF-driven all-or-none complex spikes were absent in Dab2IP-/- Purkinje cells. These results suggest that Dab2IP might regulate CF-Purkinje cell contacts along the Purkinje cell dendrites as well as electrophysiological properties of Purkinje cells. |
