OTUD7B suppresses Smac mimetic-induced lung cancer cell invasion and migration via deubiquitinating TRAF3

Background Smac mimetics are a type of drug that can induce apoptosis by antagonizing IAP family members in cancer treatment. However, a recent study showed that Smac mimetics can trigger cell invasion and migration in cancer cells by activating the NF-kappa B pathway. Methods We assessed lung cancer cell elongation, invasion and migration under treatment with the Smac mimetic LCL161. Functional analyses (in vitro and in vivo) were performed to detect the contribution of NIK and OTUD7B to LCL161-induced cell invasion and migration. The role of OTUD7B in regulation of the TRAF3/NIK/NF-kappa B pathway under LCL161 treatment was analysed by immunoblotting, immunoprecipitation, luciferase and ubiquitin assays, shRNA silencing and plasmid overexpression. Expression levels of OTUD7B, NIK and TRAF3 in tissue samples from lung cancer patients were examined by immunohistochemistry. Results We found that LCL161 stimulates lung cancer cell elongation, invasion and migration at non-toxic concentrations. Mechanistically, LCL161 results in NIK accumulation and activates the non-canonical rather than the canonical NF-kappa B pathway to enhance the transcription of target genes, such as IL-2 and MMP-9. Importantly, knockdown of NIK dramatically suppresses LCL161-induced cell invasion and migration by reducing the proteolytic processing of p100 to p52 and target gene transcription. Interestingly, we discovered that OTUD7B increases TRAF3 and decreases NIK to inhibit the non-canonical NF-kappa B pathway and that overexpression of OTUD7B suppresses LCL161-induced cell invasion and migration. Notably, OTUD7B directly binds to TRAF3 rather than to NIK and deubiquitinates TRAF3, thereby inhibiting TRAF3 proteolysis and preventing NIK accumulation and NF-kappa B pathway activation. Furthermore, the OTU domain of OTUD7B is required for the inhibition of LCL161-induced cell invasion and migration, as demonstrated by transfection of the C194S/H358R(CH) mutant OTUD7B. Finally, we investigated whether OTUD7B inhibits LCL161-induced lung cancer cell intrapulmonary metastasis in vivo, and our analysis of clinical samples was consistent with the above findings. Conclusions Our study highlights the importance of OTUD7B in the suppression of LCL161-induced lung cancer cell invasion and migration, and the results are meaningful for selecting lung cancer patients suitable for LCL161 treatment.