Generation of novel covalent RNA-protein complexes in cells by ultraviolet B irradiation: implications for autoimmunity.

OBJECTIVE: To determine whether ultraviolet B (UVB) irradiation induces novel modifications in autoantigens targeted during experimental photoinduced epidermal damage. METHODS: To search for novel UVB-induced autoantigen modifications, lysates made from UVB-irradiated human keratinocytes or HeLa cells were immunoblotted using human autoantibodies that recognize ribonucleoprotein autoantigens. Novel autoantigen structures identified were further characterized using nucleases and RNA hybridization. RESULTS: Human sera that recognize U1-70 kd (U1-70K) and La by immunoblotting also recognized multiple novel species when they were used to immunoblot lysates of UVB-irradiated keratinocytes or HeLa cells. These species were not present in control cells and were not observed when apoptosis was induced by Fas ligation or cytotoxic lymphocyte granule contents. Biochemical analysis using multiple assays revealed that these novel UVB-induced molecular species result from the covalent crosslinking between the U1 RNA and the hYRNA molecules with their associated proteins, including U1-70K, La, and likely components of the Sm particle. CONCLUSION: These data demonstrate that UVB irradiation of live cells can directly induce covalent RNA-protein complexes, which are recognized by human autoantibodies. As previously described for other autoantigens, these covalent complexes of RNA and proteins may have important consequences in terms of antigen capture and processing.

Fas ligand and Bax gene transcription contributes to Ro60 ribonucleoprotein redistribution in UV-A irradiated human keratinocytes.

OBJECTIVES: Ro ribonucleoproteins are of particular interest because they are serologic markers of photosensitive variants of lupus such as the subacute cutaneous lupus erythematosus (SCLE), in which the polycyclic skin lesions are triggered by exposure to the sun. We study the role of apoptosis in the expression of Ro antigen. METHODS: We used UV-A irradiated keratinocytes. RESULTS: We demonstrate in cultured human UVA-irradiated keratinocytes that the enhanced expression of Ro60 ribonucleoprotein is caused by antigenic redistribution consecutive to Fas-L and Bax gene activation.