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FIP200 (FAK family-interacting protein of 200 kDa) is a conserved protein recently identified as a potential mammalian counterpart of yeast autophagy protein Atg17. However, it remains unknown whether mammalian FIP200 regulates autophagy in vivo. Here we show that neural-specific deletion of FIP200 resulted in cerebellar degeneration accompanied by progressive neuronal loss, spongiosis, and neurite degeneration in the cerebellum. Furthermore, deletion of FIP200 led to increased apoptosis in cerebellum as well as accumulation of ubiquitinated protein aggregates without any deficiency in proteasome catalytic functions. We also observed an increased p62/SQSTM1 accumulation in the cerebellum and reduced autophagosome formation as well as accumulation of damaged mitochondria in the mutant mice. Lastly, analysis of cerebellar neurons in vitro showed reduced JNK activation and increased susceptibility to serum deprivation-induced apoptosis in cerebellar neurons from the mutant mice. Taken together, these results provide strong genetic evidence for a role of FIP200 in the regulation of neuronal homeostasis through its function in autophagy in vivo.

FIP200 (focal adhesion kinase family interacting protein of 200 kDa) has been shown to interact with other proteins to regulate several intracellular signaling pathways. To study a potential role of FIP200 in tumorigenesis and possibly other disease processes in vivo, we created and analyzed murine mammary tumor virus-Cre-mediated FIP200 conditional knock-out (CKO) mice. We found that deletion of FIP200 in mammary epithelial cells did not result in spontaneous development of breast cancer. Moreover, deletion of FIP200 did not further accelerate or inhibit lymphomagenesis induced by inactivation of p53 in mice. Interestingly, however, FIP200 and p53 double conditional knock-out (dCKO) mice exhibited significant hyperplasia of epidermis (acanthosis), thickening of the cornified layer (hyperkeratosis), and increased vascularity in the dermis. FIP200 CKO mice also showed similar, although less severe, skin defects as dCKO mice. Analyses of primary keratinocytes isolated from dCKO mice did not detect increased proliferation of these cells in vitro, suggesting that epidermis hyperproliferation is not epidermal cell-autonomous but may be a consequence of increased inflammation triggered by immune cells in vivo. Consistent with this possibility, we found infiltration of leukocytes including T cells, macrophages, and granulocytes into the dermis and epidermis, associated with activation of NF-κB and increased expression of several proinflammatory cytokines and chemokines in skin of the dCKO mice. We further found that cultured FIP200 KO keratinocytes showed reduced NF-κB phosphorylation in response to tumor necrosis factor α stimulation, suggesting a paracrine regulation of aberrant NF-κB activation in the skin microenviroment of dCKO and FIP200 CKO mice. Together, these results demonstrate that ablation of FIP200, although not promoting tumorigenesis, can lead to skin inflammatory disorders, suggesting a novel function of FIP200 in the maintenance of normal skin homeostasis in vivo.

Mast cells play an important role in both allergy and innate immunity. Recently, we demonstrated an active interaction between human mast cells and Pseudomonas aeruginosa leading to the production of multiple cytokines. Here, we show that both primary cultured human cord blood-derived mast cells and the human mast cell line HMC-1 undergo apoptosis as determined by single-stranded DNA (ssDNA) formation after stimulation with P. aeruginosa exotoxin A (ETA), a major toxin produced by this bacterium. ETA-induced ssDNA formation was completely inhibited by Z-VAD (where Z is benzyloxycarbonyl), which blocks multiple caspases, suggesting a role for caspases in this process. Active caspase-3 formation in mast cells after an ETA challenge was detected by both Western blotting and flow cytometry analysis. ETA-induced caspase-3 activity in human mast cells was demonstrated by the detection of a characteristic 23 kDa product of D4-GDI (where GDI is guanine nucleotide dissociation inhibitor), an endogenous caspase-3 substrate. Interestingly, a specific caspase-8 inhibitor, Z-IETD-fmk (where fmk is fluoromethyl ketone), blocked ETA-induced cleavage of D4-GDI, but a caspase-9 inhibitor (Z-LEHD-fmk) did not. Treatment of mast cells with caspase-3 inhibitor Z-DEVD-fmk or caspase-8 inhibitor Z-IETD-fmk reduced the generation of ssDNA induced by ETA, suggesting a role for caspase-8 and -3 in ETA-induced mast cell apoptosis. Furthermore, treatment of mast cells with ETA induced decreases of the short form and a long form (p43) of Fas-associated death domain protein (FADD)-like interleukin-1beta-converting enzyme (FLICE) (caspase-8)-inhibitory proteins (FLIPs), which are endogenous caspase-8 inhibitors. Taken together, these results suggest that ETA-induced mast cell apoptosis involves down-regulation of antiapoptotic proteins, FLIPs, and activation of caspase-8 and -3 pathways.

Apoptotic cells undergo characteristic morphological changes that include detachment of cell attachment from the substratum and loss of cell-cell interactions. Attachment of cells to the extracellular matrix and to other cells is mediated by integrins. The interactions of integrins with the extracellular matrix activates focal adhesion kinase (FAK) and suppresses apoptosis in diverse cell types. Members of the tumor necrosis family such as Fas and Apo-2L, also known as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), induce apoptosis in both suspension and adherent cells through the activation of caspases. These caspases, when activated, cleave substrates that are important for the maintenance of nuclear and membrane integrity. In this study, we show that FAK is sequentially cleaved into two different fragments early in Apo-2L-induced apoptosis. We also demonstrate that FAK cleavage is mediated by caspases and that FAK shows unique sensitivity to different caspases. Our results suggest that disruption of FAK may contribute to the morphological changes observed in apoptotic suspension and adherent cells.