Nuclear factor-êB (NF-êB) inducing kinase (NIK) is a MAP3K that regulates activation of NF-êB. NIK is often over-expressed in tumor cells, including melanoma, but the significance of this in melanoma progression remains unclear. Tissue microarray analysis of NIK expression reveals that dysplastic nevi (n=22), primary (n=15) and metastatic melanoma (n=13) lesions showed a statistically significant elevation in NIK expression when compared to benign nevi (n=30). Depletion of NIK using shRNA in melanoma cell lines decreased proliferation, increased apoptosis, delayed cell cycle progression, and reduced tumor growth in a mouse xenograft model. Consistent with the previous studies, NIK deficiency reduced activation of the non-canonical NF-êB pathway, while canonical NF-êB activation remained intact. NIK depletion also reduced expression of genes that contribute to tumor growth, including CXCR4, c-MYC and c-MET, as well as pro-survival factors BCL2 and survivin. These changes in gene expression are not fully explained by the attenuation of the non-canonical NF-êB pathway. Shown here for the first time is the demonstration that NIK depletion decreases â-catenin mediated transcription to down-regulate expression of survivin as well as other â-catenin regulated genes including c-MYC, c-MET and CCND2. These data indicate NIK mediates both â-catenin and NF-êB regulated transcription to modulate melanoma survival and growth. Thus, NIK may be a promising therapeutic target for melanoma. In addition, novel NIK-interacting proteins were identified by using mass spectrometry analysis. Some of these proteins include heat shock protein 90 (Hsp90), ribosomal protein S3 (RPS3) and DEAD box polypeptide 5 (DDX5).
Inhibitor of IêB kinase â (IKKâ), another kinase of NF-êB pathway, also contributes to melanoma growth. Systemic inhibition of this kinase in a melanoma xenograft model was characterized using a pharmacological IKKâ inhibitor, BMS-345541. Results show that inhibition of IKKâ alters the host immune cell composition and the composition of leukocytes infiltrating tumor, suggesting that systemic NF-êB inhibition should be evaluated more carefully before going forward as a cancer therapy.
In this research, I identified NIK as a new potential target for melanoma growth, revealed important new biological functions of NIK, and unraveled key effects of IKKâ inhibition on the tumor microenvironment.