Vascular smooth muscle cells express a constitutive NF-kappa B-like activity.

The NF-kappa B/Rel family of transcription factors is commonly expressed in non-hematopoietic cells in an inactive form within the cytoplasm, complexed with an inhibitor I kappa B protein. Thus, it was surprising that NF-kappa B element-driven heterologous promoter-reporter gene constructs were active upon transient transfection into vascular smooth muscle cells (VSMCs). Here, we report that VSMCs express a constitutive nuclear NF-kappa B-like activity. In electrophoretic mobility shift assays, nuclear extracts demonstrated binding to a wild type NF-kappa B element but not to those mutated at nucleotides critical for Rel-protein DNA interaction. Binding was abrogated by the presence of I kappa B-alpha. Furthermore, addition of an antibody to the p50 subunit of classical NF-kappa B (but not p65, c-Rel, or RelB) resulted in supershifted complexes. Transactivation of element-driven constructs was negatively affected by co-transfection of a vector expressing a dominant negative p50 subunit, which can dimerize with other Rel subunits but not bind DNA. The long terminal repeat of the human immunodeficiency virus-1, which is driven in part by two NF-kappa B elements, displayed strong activity within VSMCs. This activity was abrogated upon co-transfection of the vector expressing the dominant negative p50 mutant. Taken together, these experiments indicate that VSMCs constitutively express a functional NF-kappa B-like trans-acting factor, which may play a significant role in the regulation of proliferation and viral infection of these cells.