NF-κB determines localization and features of cell death in epidermis

Abstract

Figure 1Generation of epithelial cells with altered NF-κB function. Normal keratinocytes were transduced with retroviral expression vector for (a) lacZ normal control, (b) constitutively active p50, and (c) the trans-dominant IκBαM super-repressor, then subjected to immunofluorescence staining with antibody to p50 (bars = 5 µm). Note marked nuclear expression in p50-transduced cells and blockade of nuclear-localized p50 in IκBαM.NF-κB subunit transcription activation domains in that these changes are not observed with transcriptionally inactive mutants; the basis for this effect is unclear. This approach, however, has been shown previously to produce the predicted respective induction or blockade of NF-κB-driven gene expression in epithelial cells, both in the case of p50 and p65 alone as well as both subunits together (21) and provides a basis for determining the effects altering NF-κB function on apoptosis in this setting.Fas is expressed in epithelial cells and is implicated as a potentially important mediator of epithelial cell death in settings of inflammation (33-35) and ultraviolet injury (5,36). Cotransduction with vectors altering NF-κB function and a retroviral vector for human Fas/CD95 was used to study NF-κB effects on Fas-triggered apoptosis in epithelial cells. Fas activation in normal control and in IκBαM[+] cells leads to rapid cellular rounding, shrinkage, and detachment in the majority of cells; however, these changes are not seen in NF-κB subunit-expressing cells (Figure 2, a-c and f). These morphologic changes are consistent with apoptosis, a possibility supported by detection of DNA strand breakage using TUNEL assay and characteristic nuclear morphologic condensation and collapse in these cells (Figure 2, d and e).TNFα is another known trigger of apoptosis in many tissues that also impacts NF-κB function. TNFα activation of NF-κB through the TNF receptor TNFR1 opposes TNFα-induced apoptosis in a number of cell types in a process dependent on TRAF2 (8, 37). Whereas TNFα failed to alter normal keratinocytes or those expressing active NF-κB subunits, NF-κB blockade renders these cells very susceptible to TNFα-induced apoptosis (Figure 3, a-d), suggesting an analogous role for NF-κB in preventing apoptosis in epithelial cells.Blockade of NF-κB function leads to premature epidermal cell apoptosis in vivo. Normal stratified epithelium maintains a balance between cellular proliferation and a specialized form of programmed cell death confined to the outer differentiated cell layer at the stratum granulosum-stratum corneum interface (4). This terminal differentiation-associated cell death is not accompanied by classic cell morphologic features of apoptosis such as cell shrinkage and collapse, membrane blebbing, and nuclear condensation seen in other cell death settings in epithelium such as infection and ultraviolet injury (38). NF-κB translocates into nuclei of cells within outer layers of stratified epithelium (21), and this translocation is accompanied by NF-κB target gene activation (K. Hinata et...

Current insights into the regulation of programmed cell death by NF-κB

“…Although NF-kB is generally implicated in cancer by virtue of its ability to drive cell proliferation and survival, the inhibition of NF-kB in epidermal cells is associated with increased proliferation and hyperplasia (Seitz et al, 1998;van Hogerlinden et al, 1999;Seitz et al, 2000). Furthermore, inhibition of NF-kB activity combined with expression of oncogenic Ras in epidermal keratinocytes leads to invasive neoplasia with features similar to those of squamous cell carcinoma (Dajee et al, 2003).…”

Death penalty for keratinocytes: apoptosis versus cornification

“…44,45 In general, NF-kB activation results in protection against apoptosis by upregulating antiapoptotic genes such as members of the Bcl-2 family and cellular inhibitors of apoptosis (c-IAPs). In addition, NF-kB can also act as a positive regulator of cell cycle progression and it has been implicated in invasion and metastatic growth of tumor cells.…”

“…44 In addition, transgenic overexpression of dominant negative IkBa in murine skin results in premature spontaneous cell death exhibiting apoptotic properties. 45 This suggests an important role for NF-kB in protection of keratinocytes against apoptosis when the cells undergo the program of cornification.…”

Is psoriasis a T‐cell disease?

“…keratinocytes, fibroblasts, etc). As several groups are now focusing on the importance of NF-kB-mediated signaling by keratinocytes in-vitro and in-vivo, rapid progress in this area is likely to be forthcoming, and of potential relevance to psoriasis (24)(25)(26)(27)(28)(29).…”