Inflammatory diseases at epithelial borders develop from aberrant interactions between resident cells of the tissue and invading immunocytes. Here, we unraveled basic functions of epithelial cells and immune cells and the sequence of their interactions in an inflammatory skin disease. Ubiquitous deficiency of the IkappaBalpha protein (Ikba(Delta)(/Delta)) as well as concomitant deletion of Ikba specifically in keratinocytes and T cells (Ikba(K5Delta/K5Delta lckDelta/lckDelta)) resulted in an inflammatory skin phenotype that involved the epithelial compartment and depended on the presence of lymphocytes as well as tumor necrosis factor and lymphotoxin signaling. In contrast, mice with selective ablation of Ikba in keratinocytes or lymphocytes showed inflammation limited to the dermal compartment or a normal skin phenotype, respectively. Targeted deletion of RelA from epidermal keratinocytes completely rescued the inflammatory skin phenotype of Ikba(Delta)(/Delta) mice. This finding emphasizes the important role of aberrant NF-kappaB activation in both keratinocytes and lymphocytes in the development of the observed inflammatory skin changes.

Hematopoiesis occurs in the liver and the bone marrow (BM) during murine development. Newborn mice with a ubiquitous deletion of I kappa B alpha develop a severe hematological disorder characterized by an increase of granulocyte/erythroid/monocyte/macrophage colony-forming units (CFU-GEMM) and hypergranulopoiesis. Here, we report that this particular myeloproliferative disturbance is mediated by continuously deregulated perinatal expression of Jagged1 in I kappa B alpha-deficient hepatocytes. The result is a permanent activation of Notch1 in neutrophils. In contrast, in mice with a conditional deletion of I kappa B alpha only in the myeloid lineage (ikba(flox/flox) x LysM-Cre) and in fetal liver cell chimeras (ikba(FL delta/FL delta)), a cell-autonomous induction of the myeloproliferative disease was not observed. Coculture of I kappa B alpha-deficient hepatocytes with wild-type (wt) BM cells induced a Jagged1-dependent increase in CFUs. In summary, we show that cell-fate decisions leading to a premalignant hematopoietic disorder can be initiated by nonhematopoietic cells with inactive I kappa B alpha.

Sulfur mustard (SM) is a strong vesicant that has been used as a chemical warfare agent. To understand the molecular mechanisms that underlie the inflammatory skin reaction in response to SM, we analyzed the activation pattern of the NF-kappaB and mitogen-activated protein kinase (MAPK) pathways. Keratinocytes responded with an induction of the canonical NF-kappaB pathway, including activation of IkappaB kinase 2, followed by phosphorylation and degradation of IkappaBalpha and of the transactivating subunit RelA at Ser536. The biphasic NF-kappaB response was strictly dependent on the transactivating subunit RelA, as demonstrated by keratinocytes lacking RelA. Parallel to NF-kappaB activation, we observed an induction of the Raf-1/MEK1/2/ERK1/2/MSK1 and MKK3/6/p38/MSK1 pathways. Although mitogen and stress-activated kinase 1 has been described as a RelA kinase with Ser276 as its target, this site remained unphosphorylated in response to SM. A further MAPK pathway induced by SM was the MKK4/7/JNK1/2 pathway, which resulted in phosphorylation of the transcription factor activating transcription factor-2, but not c-Jun. Our results indicate that SM induces a complex cellular response in keratinocytes, with the activation of three MAPK pathways and the NF-kappaB pathway.

No abstract

Hematopoiesis occurs in the liver and the bone marrow during murine development. Newborn mice with a ubiquitous deletion of IκBα develop a severe hematological disorder characterized by an increase of granulocyte/erythroid/monocyte/macrophage colony-forming units (CFU-GEMM) and hypergranulopoiesis. Here, we provide evidence that this particular myeloproliferative disturbance is mediated by continuously deregulated perinatal expression of the Notch ligand Jagged1 in IκBα-deficient hepatocytes. Signaling through Notch-family cell surface receptors and their ligands has been shown to be involved in cell fate decisions of stem cells during hematopoietic/mesenchymal differentiation. However, the role of Notch signaling in myelopoiesis is still under discussion as results gained using different experimental conditions are contradictory. Due to embryonic lethality of Notch1- and Jagged1-deficient mice, alterations of myelopoiesis are difficult to be adressed. In this study, we investigated the function of IκBα and its role within the Jagged/Notch signaling pathway during myelopoiesis. Therefore, a novel mouse line with a conditional (floxed) allele of ikba was established. Ubiquitous deletion of IκBα after cross-breeding with Deleter-Cre mice results in hypergranulopoiesis comparable to the conventional deletion of the allele. A detailed analysis revealed a myeloproliferative syndrome with increased numbers of cycling progenitor cells. The morphological analysis of liver and bone marrow of IκBα-deficient mice showed hypercellularity. The cellular components were dominated by myeloid lineages and represented mostly granulocyts with dysplastic features, characterized by pseudo-Pelger-Huet formation. Myelodysplasia could also be detected in megakaryopoiesis by the presence of micromegakaryocytes. Alterations in erythropoiesis were detectable by condensed chromatin and an asychrony of the nucleocytoplasmic ratio in the red cell precursor population. Together, our results indicate that ubiquitous loss of IκBα results in hypergranulopoiesis progressing to a myelodysplastic syndrome. Systematic analysis of transcription factors, growth factor receptors and NF-κB-regulated cell-survival genes was performed to determine molecular mechanisms underlying hypergranulopoiesis. Our data suggested that Notch1-dependent signals were responsible for the myeloproliferative disorder as Notch1 was upregulated in neutrophils and the Notch ligand Jagged1 in non-hematopoietic cells, namly hepatocytes. Myeloproliferation could be inhibited by blocking the Notch1 ligand Jagged1. Interestingly, deletion of IκBα in neutrophils and macrophages or hematopoietic stem cells did not result in dysregulation of myelopoiesis despite constitutive NF-κB activation in these cells. This establishes the relevance of non-hematopoietic expression of Jagged1 for the control and regulation of myelopoiesis. In summary, we show that cell-fate decisions leading to a premalignant hematopoietic disorder can be initiated by non-hematopoietic cells with inactive IκBα.