The IDDM-associated solitary retroviral promoters DQ-LTR3 and DQ-LTR13 have a distinct impact on the expression of selected DQB1 genes in different cell lines in vitro.

The HLA complex on chromosome 6, especially of the HLA class II genes, plays an important role in the pathogenesis of insulin-dependent diabetes mellitus (IDDM). Three solitary long terminal repeats (LTRs) have been described in the vicinity of HLA DQ, two of them modifying the genetic susceptibility to type 1 diabetes on high-risk HLA DQ haplotypes. Therefore, we have investigated the putative regulatory properties of these retroviral promoters in different cell lines, including a number of B- and T-lymphoblastoid cell lines bearing different DQ haplotypes, employing a transient reporter gene assay. The transcriptional activity of appropriate constructs harboring an LTR linked to the luciferase reporter gene revealed different expression patterns which varied considerably between the investigated cell lines. DQ-LTR3 showed clear activities, whereby the levels of luciferase gene expression were also increased approximately 200-fold in the teratocarcinoma cell line GH. For the different B- and T-cell lines, no significant activity was detected for any of the investigated LTRs. Furthermore, we have analyzed the effect of DQ-LTR13 on distinct DQB1 promoters and could show an increased activity of the DQB1*0302 promoter under the influence of DQ-LTR13. It varied from 1.5- to 6-fold in different cell lines depending on the transcriptional orientation and position of the LTR and was independent of DQ-LTR3. Moreover, the impact of the LTR was different for the DQB1*0201 promoter demonstrating a decreasing effect. These data indicate that a DQ-LTR13-mediated impact on the DQB1 promoter activity exists which differs clearly between selected promoters.