Deletion of Gab adaptor proteins leads to impaired macrophage development and chronic colitis (P4175)

Inflammatory Bowel Disease (IBD), commonly Crohn’s and Ulcerative Colitis, is characterized by chronic inflammation of the gastrointestinal tract. Although the cause of this disorder is not known, alterations in immune responses and uncontrolled intestinal microflora are thought to be involved. Our lab has uncovered an important role for the Grb2 associated binding (Gab) adaptor protein family in the development and pathogenesis of IBD. In mice, Gabs include three family members that play critical regulatory roles in modulating cytokine receptor signaling in T-cells and macrophage. Our studies demonstrate that knock-out (KO) of only two of these, Gab2/3, leads to intestinal inflammation associated with spontaneous rectal prolapse as early as 8 weeks of age that is not observed in single KO mice. Bone marrow derived macrophage (BMDM) cultured from mice lacking Gab2/3 expanded poorly compared to wild-type mice or mice lacking only Gab2 or Gab3 but expressed mature markers. RT-PCR analysis showed dysregulated expression of both pro- and anti-inflammatory cytokines. Importantly, pro-inflammatory cytokines IL-6, TNF-α, IL-12p40 were significantly induced in Gab2/3 KO BMDM compared to control. Upon TLR4 activation, Gab2/3 KO cells had prolonged activation of signaling molecules IκBα and NFκB. Together these data support our conclusion that Gabs play a critical role in the pathogenesis of IBD and provide insight toward new therapeutic approaches to control and treat IBD.

Acquired alkylating drug resistance of a human ovarian carcinoma cell line is unaffected by altered levels of pro- and anti-apoptotic proteins

In a systematic study to elucidate the involvement of pro- and anti-apoptotic proteins in alkylating drug resistance of tumor cells, we utilized the A2780(100) line, that was selected by repeated exposure of A2780 cell line (human ovarian carcinoma line) to chlorambucil (CBL). A2780(100) was 5 - 10-fold more resistant to nitrogen mustards (IC50 of 50 - 60 microM) and other DNA crosslinking agents, e.g., cisplatin, and also to DNA topoisomerase inhibitor etoposide (ETO) than A2780. CBL (125 microM) induced extensive apoptosis in A2780 associated with mitochondrial damage but not in A2780(100). No significant differences were observed between A2780 and A2780(100) cells in the basal levels, or the enhanced levels in some cases after CBL treatment, of DNA repair proteins involved in repair of alkyl base adducts or in repair of DNA crosslinks or double strand break repair. However, the basal levels of anti-apoptotic proteins Bcl-xL and Mcl-1 were 4 - 8-fold higher in A2780(100) than in A2780 neither of which expressed Bcl-2. In contrast, the levels of pro-apoptotic Bax and Bak were 3 - 5-fold higher in the CBL-treated A2780 but not in A2780(100). ETO (5 microM) induced apoptosis in A2780 without altering the levels of Bax and Bak in these cells. At the same time, neither overexpression of Bcl-xL in A2780, nor its antisense expression in A2780(100), and nor overexpression of Bax in A2780(100), significantly affected drug sensitivity of either line. Our results suggest that a change in an early step in DNA damage processing which affects intracellular signaling, such as enhanced DNA double-strand break repair, could be the primary cause for development of resistance in A2780(100) cells to drugs which induce DNA crosslinks or double strand-breaks.