The lymphotoxin-β receptor is an upstream activator of NF-κB-mediated transcription in melanoma cells

The pleiotropic transcription factor nuclear factor-κB (NF-κB (p50/p65)) regulates the transcription of genes involved in the modulation of cell proliferation, apoptosis, and oncogenesis. Furthermore, a host of solid and hematopoietic tumor types exhibit constitutive activation of NF-κB (Basseres, D. S., and Baldwin, A. S. (2006) 25, 6817-6830). However, the mechanism for this constitutive activation of NF-κB has not been elucidated in the tumors. We have previously shown that NF-κB-inducing kinase (NIK) protein and its association with Inhibitor of κB kinase αβ are elevated in melanoma cells compared with their normal counterpart, leading to constitutive activation of NF-κB. Moreover, expression of dominant negative NIK blocked this base-line NF-κB activity in melanoma cells. Of the three receptors that require NIK for activation of NF-κB, only the lymphotoxin-β receptor (LTβ-R) is expressed in melanoma. We show in this manuscript that for melanoma there is a strong relationship between expression of the LTβ-R and constitutive NF-κB transcriptional activity. Moreover, we show that activation of the LTβ-R can drive NF-κB activity to regulate gene expression that leads to enhanced cell growth. The inhibition by LTβ-R shRNA resulted in decreased NF-κB promoter activity, decreased growth, and decreased invasiveness as compared with control. These results indicate that the LTβ-R constitutively induces NF-κB activation, and this event may be associated with autonomous growth of melanoma cells.