c-Rel is a cell cycle modulator in human melanoma cells.

Melanoma progression and resistance to therapy are associated with faulty regulation of signalling molecules including the central transcription factor NF-κB. Increased expression of the c-Rel subunit of NF-κB has been described in progressing melanoma, though mechanistic implications of this upregulation remain unclear. To elucidate the functional role of c-Rel in melanoma biology, we have assessed its expression in human melanoma as well as in melanoma cell lines. Suppression of c-Rel expression in four melanoma cell lines resulted in reduced growth and altered cell cycle regulation, namely G2/M and polyploid phase induction. Moreover, mitotic spindle morphology was profoundly altered in three of the cell lines with a predominance of monopolar structures. These findings suggest that c-Rel is involved in G2/M phase regulation, prevention of polyploidy and, consequently, chromosomal stability. Our results highlight a novel tumor-promoting function of c-Rel in human melanoma cells through governing cell cycle regulation.

The IKKα-dependent non-canonical pathway of NF-κB activation is constitutively active and modulates progression-related functions in a subset of human melanomas.

Owing to activation of several resistance-mediating pathways including NF-κB signaling, metastasized melanoma is almost universally resistant against chemotherapy. Given that blocking of NF-κB either by proteasome-, pan-IKK- or selective IKKß-inhibitors may increase the susceptibility of melanoma cells to chemotherapy, we have assessed the role of the second kinase within the IKK complex, IKKα. While expression of IKKα and overall activation of NF-κB were heterogeneous, the IKKα-specific p100/p52 processing was detected in a small subset of melanomas (1/9 primary and 1/12 metastatic melanomas) as well as in 1/8 melanoma cell lines. Down-modulation of IKKα by siRNA resulted in diminution of doxorubicin-induced NF-κB activation, constitutive and TNFα-stimulated expression of CXCL8 and ICAM-1, and cell migration. In contrast, overexpression of IKKα in melanoma cells did not significantly affect progression-related functions. Thus, IKKα may be a worthwhile target only in selected individualized therapies but not in general melanoma therapy.

Integrin αE (CD103) is induced but plays no pathogenic role in psoriasiform skin lesions of TGFß1 transgenic mice.

T-cells expressing αE (CD103), an integrin induced by TGFß on T-cells in vitro, accumulate within epithelia in inflammatory disorders, including psoriasis. However, it is unclear, if and how αE (CD103) contributes to skin inflammation. Using two complementary approaches, we have investigated αE (CD103) in psoriasis-like skin inflammation of mice with transgenic epidermal expression of human TGFß1: αE (CD103) was inhibited by function-blocking antibodies in vivo, and double-mutants with additional αE (CD103)-depletion were generated in two different genetic backgrounds. Epidermal hTGFß1 expression was associated with prominent expression of αE (CD103) on infiltrating cells. However, neither treatment with αE (CD103)-blocking antibodies nor deficiency of αE (CD103) in double-mutant mice altered the psoriasis-like phenotype. In addition, histopathological and flow cytometric analyses revealed similar pathological skin alterations and lymphocyte subgroups in the different mouse strains. Thus, while αE (CD103) expression is indeed associated with hTGFß1 in vivo, it has little, if any, influence on the course of the psoriasis-like phenotype in K5.hTGFß1 transgenic mice.

Integrin αE(CD103) Is Involved in Regulatory T-Cell Function in Allergic Contact Hypersensitivity.

Murine contact hypersensitivity (CHS) is a dendritic cell (DC)-dependent T-cell-mediated inflammation with CD8+ T cells as effectors and CD4+ T cells as regulators (Treg cells) that models human allergic contact dermatitis. The integrin αE(CD103) is expressed by some T-cell and DC subsets and has been implicated in epithelial lymphocyte localization, but its role in immune regulation remains enigmatic. We have identified a function for CD103 in the development of cutaneous allergic immune responses. CHS responses, but not irritant contact dermatitis, were significantly augmented in CD103-deficient mice in hapten-challenged skin. Phenotype and function of skin DCs during sensitization were normal, whereas adoptive transfer experiments revealed that the elevated CHS response in CD103-deficient mice is transferred by primed T cells and is independent of resident cells in recipient mice. While T-cell counts were elevated in challenged skin of CD103-deficient mice, the FoxP3 expression level of CD4+CD25+ Treg cells was significantly reduced, indicating impaired functionality. Indeed, Treg cells from CD103-deficient mice were not able to suppress CHS reactions during the elicitation phase. Further, CD103 on FoxP3+ Treg cells was involved in Treg retention to inflamed skin. These findings indicate an unexpected dichotomous functional role for CD103 on Treg cells by modulating FoxP3 expression.