Pdcd4 is a novel transformation suppressor that inhibits tumor promoter-induced neoplastic transformation and the activation of AP-1-dependent transcription required for transformation. A yeast two-hybrid analysis revealed that Pdcd4 associates with the eukaryotic translation initiation factors eIF4AI and eIF4AII. Immunofluorescent confocal microscopy showed that Pdcd4 colocalizes with eIF4A in the cytoplasm. eIF4A is an ATP-dependent RNA helicase needed to unwind 5 mRNA secondary structure. Recombinant Pdcd4 specifically inhibited the helicase activity of eIF4A and eIF4F. In vivo translation assays showed that Pdcd4 inhibited cap-dependent but not internal ribosome entry site (IRES)-dependent translation. In contrast, Pdcd4 D418A , a mutant inactivated for binding to eIF4A, failed to inhibit cap-dependent or IRES-dependent translation or AP-1 transactivation. Recombinant Pdcd4 prevented eIF4A from binding to the C-terminal region of eIF4G (amino acids 1040 to 1560) but not to the middle region of eIF4G(amino acids 635 to 1039). In addition, both Pdcd4 and Pdcd4 D418A bound to the middle region of eIF4G. The mechanism by which Pdcd4 inhibits translation thus appears to involve inhibition of eIF4A helicase, interference with eIF4A association-dissociation from eIF4G, and inhibition of eIF4A binding to the C-terminal domain of eIF4G. Pdcd4 binding to eIF4A is linked to its transformation-suppressing activity, as Pdcd4-eIF4A binding and consequent inhibition of translation are required for Pdcd4 transrepression of AP-1.

Pulmonary fibrosis is the pathologic basis for a variety of incurable human chronic lung diseases. IL-17A, a glycoprotein secreted from IL-17–producing cells, has recently been shown to be a proinflammatory cytokine involved in chronic inflammation and autoimmune disease. In this study, we report that IL-17A increased the synthesis and secretion of collagen and promoted the epithelial–mesenchymal transition in alveolar epithelial cells in a TGF-β1–dependent manner. Using in vivo fibrotic models, we found IL-17A expression to be elevated and IL-17A–associated signaling pathways to be activated in fibrotic lung tissues. Neutralization of IL-17A in vivo promoted the resolution of bleomycin-induced acute inflammation, attenuated pulmonary fibrosis, and increased survival. Additionally, IL-17A antagonism inhibited silica-induced chronic inflammation and pulmonary fibrosis. Targeting IL-17A resulted in a shift of the suppressive immune response in fibrotic lung tissue toward a Th1-type immune response, and it effectively induced autophagy, which promoted the autophagic degradation of collagen and autophagy-associated cell death. Moreover, IL-17A was found to attenuate the starvation-induced autophagy, and autophagy modulators regulated collagen degradation in the alveolar epithelial cells in a TGF-β1–independent manner. Administration of 3-methylamphetamine, an autophagy inhibitor, reversed the therapeutic efficacy of IL-17A antagonism in pulmonary fibrosis. Our studies indicate that IL-17A participates in the development and progression of pulmonary fibrosis in both TGF-β1–dependent and –independent manners and that the components of the IL-17A signaling pathway are potential therapeutic targets for the treatment of fibroproliferative lung diseases.

〈n ␣-helical MA-3 domain appears in several translation initiation factors, including human eukaryotic translation initiation factor 4G (eIF4G) and DAP-5/NAT1/p97, as well as in the tumor suppressor Pdcd4. The function of the MA-3 domain is, however, unknown. C-terminal eIF4G (eIG4Gc) contains an MA-3 domain that is located within the eIF4A-binding region, suggesting a role for eIF4A binding. Interestingly, C-terminal DAP-5/NAT1/p97 contains an MA-3 domain, but it does not bind to eIF4A. Mutation of amino acid residues conserved between Pdcd4 and eIF4Gc but not in DAP-5/NAT1/p97 to the amino acid residues found in the DAP-5/NAT1/p97 indicates that some of these amino acid residues within the MA-3 domain are critical for eIF4A-binding activity. Translation initiation of capped mRNA is proposed to occur by a ribosomal scanning mechanism (20). A 43S ribosomal complex comprised of a 40S ribosomal subunit, the initiator Met-tRNAi, and translation initiation factors binds to the cap structure of mRNA at the 5Ј end and scans downstream along the 5Ј-untranslated region (5ЈUTR) searching for the initiation codon. The rate-limiting step for this process is the binding of the 40S ribosomal subunit to mRNA. Several eukaryotic translation initiation factors (eIFs), including the critical factor eIF4A, participate in this process.Translation initiation factor eIF4A is a member of the DEAD-box RNA helicase protein family. The DEAD-box family proteins catalyze RNA unwinding and/or rearrangement. eIF4A is an ATP-dependent RNA helicase that functions in translation initiation to catalyze the unwinding of mRNA secondary structure at the 5ЈUTR (36

Pdcd4 is a novel transformation suppressor that is highly expressed in promotion-resistant (P7) mouse epidermal JB6 cells but not in susceptible (P+) cells. Overexpression of pdcd4 cDNA in stably transfected P+ cells rendered cells resistant to tumor promoter-induced transformation, indicating that elevated expression of Pdcd4 protein is su cient to suppress neoplastic transformation. To determine whether Pdcd4 suppresses neoplastic transformation through inhibiting known transformation required events, we examined the possibility that pdcd4 inhibited the activation of AP-1 or NF-kB dependent transcription or of ornithine decarboxylase (ODC) activity. Activation of AP-1-dependent transcriptional activity was inhibited by pdcd4 expression in a concentration dependent manner. In contrast, Pdcd4 slightly increased NF-kB-dependent transcription and did not alter ODC enzymatic activity. Previous studies suggested that activation of AP-1 was required for P+ cell transformation as well as for tumor promotion in vivo. These results indicate that Pdcd4 functions as a transformation suppressor, possibly through inhibiting AP-1 activation in combination with other factors such as enhancing NF-kB activation. Pdcd4 may thus constitute a useful molecular target for cancer prevention. Oncogene (2001) 20, 669 ± 676.