The L1 retroelement-related p40 protein induces p38delta MAP kinase.
We characterized a full length L1 mRNA in a rheumatoid arthritis (RA) synovial tissue and determined the degree of methylation of its 5'-UTR. We asked whether not only intact but also altered L1s can exert biological activities by transfecting RA synovial fibroblasts (SF) with either retrotransposition-competent or incompetent L1s and examined their capacity to induce p38delta. Total RNA was isolated from the synovial tissue of a 35-year-old woman with highly destructive RA. A complete L1 sequence was obtained by 3'/5'-RACE. Methylation of the genomic 5'-UTR was determined by the sodium-disulfide/PCR method. RA-SF were transfected by lipofection with either a functional L1 or an ORF2-mutated L1 element. The expression of p38delta was measured by RT-PCR and Western blot. The full length L1 mRNA included a 5'-UTR, an ORF1 and an ORF2. Three of five CpG islands (60%) of the genomic L1 5'-UTR were hypomethylated and the ORF2 was deactivated by the insertion of stop codons. Both, intact and ORF2-mutated L1 vectors, induced the expression of p38delta. Thus, even an ORF2-mutated L1 element, as expressed in RA, is biologically active and both L1 ORF1 and p38delta transcripts may appear as a consequence of genomic hypomethylation. The induction of p38delta appears to be mediated by an ORF1/p40-dependent process. This is the first indication of a p40 mediated transactivation.
Kuchen
Stefan
S
Center of Experimental Rheumatology, Department of Rheumatology, University Hospital, CH-8091 Zürich, Switzerland.
Seemayer
Christian A
CA
Rethage
Janine
J
von Knoch
Rebecca
R
Kuenzler
Peter
P
Beat
A Michel
AM
Gay
Renate E
RE
Gay
Steffen
S
Neidhart
Michel
M
D001172:Arthritis, Rheumatoid / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D048292:Mitogen-Activated Protein Kinase 13; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018626:Retroelements / Q000235:genetics*
D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D018626:Retroelements; C077214:L1Hs-encoded protein p40, human; D048292:Mitogen-Activated Protein Kinase 13; D020928:Mitogen-Activated Protein Kinases