Numerous genes required during the immune or inflammation response as well as the adhesion process are regulated by nuclear factor B (NF-B). Associated with its inhibitor, IB, NF-B resides as an inactive form in the cytoplasm. Upon stimulation by various agents, IB is proteolyzed and NF-B translocates to the nucleus, where it activates its target genes. The transduction pathways that lead to IB inactivation remain poorly understood. In this study, we have characterized a cellular mutant, the 70/Z3-derived 1.3E2 murine pre-B cell line, that does not activate NF-B in response to several stimuli. We demonstrate that upon stimulation by lipopolysaccharide, Taxol, phorbol myristate acetate, interleukin-1, or double-stranded RNA, IB␣ is not degraded, as a result of an absence of induced phosphorylation on serines 32 and 36. Neither a mutation in IB␣ nor a mutation in p50 or relA, the two major subunits of NF-B in this cell line, accounts for this phosphorylation defect. As well as culminating in the inducible phosphorylation of IB␣ on serines 32 and 36, all the stimuli that are inactive on 1.3E2 cells exhibit a sensitivity to the antioxidant pyrrolidine dithiocarbamate (PDTC). In contrast, stimuli such as hyperosmotic shock or phosphatase inhibitors, which use PDTC-insensitive pathways, induce IB␣ degradation in 1.3E2. Analysis of the redox status of 1.3E2 does not reveal any difference from wild-type 70Z/3. We also report that the human T-cell leukemia virus type 1 (HTLV-1)-derived Tax trans-activator induces NF-B activity in 1.3E2, suggesting that this viral protein does not operate via the defective pathway. Finally, we show that two other IB molecules, IB␤ and the recently identified IB, are not degraded in the 1.3E2 cell line following stimulation. Our results demonstrate that 1.3E2 is a cellular transduction mutant exhibiting a defect in a step that is required by several different stimuli to activate NF-B. In addition, this analysis suggests a common step in the signaling pathways that trigger IB␣, IB␤, and IB degradation.

The molecular biology of lymphatics is only rudimentary owing to the long-standing absence of specific markers, and scanty is the information regarding bladder lymphatic vessels. By using mice with a reporter gene for nuclear factor B (NF-B) activity (B-lacZ) in combination with immunohistochemical staining with a specific lymphatic marker (LYVE-1), we show, for the first time, that NF-B is constitutively active in lymphatic endothelium in the urinary bladder, uterus, intestine, heart, and airways. Tie2-lacZ mice confirmed that the structures observed in B-lacZ mice were not blood vessels. In addition, acute instillation of lipopolysaccharide (LPS) or tumor necrosis factor ␣ (TNF-␣) into the B-lacZ mouse bladder revealed the capacity of this transgenic in reporting inducible NF-B activity. Our findings demonstrate an overriding constitutive NF-B activity in the lymphatic system. They also provide a working model for detecting lymphatic vessels and evoke testable hypotheses regarding the role of lymphatic vessels in health and disease. (Blood. 2004;104:3228-3230)