TNFα can trigger different signaling pathways, including the JNK pathway, to regulate various biological functions such as cell death, differentiation and proliferation. The scaffold protein POSH (Plenty of SH3 Domains) has been shown to be an important regulator of the JNK pathway, but whether it is involved in TNF-signaling has not been reported. Although POSH has been implicated to play a role in development in zebrafish, it has not been studied in null mutants and the underlying mechanism of its effects is still not clear. In this study, we provide evidence that the JNK pathway scaffold protein, POSH, is involved in TNF (Eiger) signaling in Drosophila. POSH is likely to act downstream of dTAB2 and upstream of dTAK1 in the TNF-JNK signaling pathway. In addition, we found that POSH is essential during Drosophila embryogenesis, including epidermal dorsal closure, similar to other JNK pathway components such as Silpper, Hemipterous, and Basket. We observed defects in F-actin accumulation and adherens junction formation during dorsal closure in different posh null mutants, suggesting that POSH is required for epidermal cell migration and cell-shape change during epidermal dorsal closure.