A role for the non-receptor tyrosine kinase ACK1 in TNF-alpha-mediated apoptosis and proliferation in human intestinal epithelial caco-2 cells.

The roles of tumor necrosis factor alpha (TNF-alpha) and its mediators in cellular processes related to intestinal diseases remain elusive. In this study, we aimed to determine the biological role of activated Cdc42-associated kinase 1 (ACK1) in TNF-alpha-mediated apoptosis and proliferation in Caco-2 cells. ACK1 expression was knocked down using ACK1-specific siRNAs, and ACK1 activity was disrupted using a small molecule ACK1 inhibitor. The Terminal deoxynucleotidyl transferase biotin-dUTP Nick End Labeling (TUNEL) and the BrdU incorporation assays were used to measure apoptosis and cell proliferation, respectively. ACK1-specific siRNA and the pharmacological ACK1 inhibitor significantly abrogated the TNF-alpha-mediated anti-apoptotic effects and proliferation of Caco-2 cells. Interestingly, TNF-alpha activated ACK1 at tyrosine 284 (Tyr284), and the ErbB family of proteins was implicated in ACK1 activation in Caco-2 cells. ACK1-Tyr284 was required for protein kinase B (AKT) activation, and ACK1 signaling was mediated through recruiting and phosphorylating the down-stream adaptor protein AKT, which likely promoted cell proliferation in response to TNF-alpha. Moreover, ACK1 activated AKT and Src enhanced nuclear factor-кB (NF-кB) activity, suggesting a correlation between NF-кB signaling and TNF-alpha-mediated apoptosis in Caco-2 cells. Our results demonstrate that ACK1 plays an important role in modulating TNF-alpha-induced aberrant cell proliferation and apoptosis, mediated in part by ACK1 activation. ACK1 and its down-stream effectors may hold promise as therapeutic targets in the prevention and treatment of gastrointestinal cancers, in particular, those induced by chronic intestinal inflammation.

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