The biologically active synthetic retinoid CD437 (6-[3-adamantyl-4-hydroxyphenyl]-2-naphthalene, AHPN) and different human breast carcinoma (HBC) cell lines were used to examine the possible mechanism(s) of gadd45 induction. Northern blot analysis of mRNA isolated from MCF-7, MDA-MB-468 and MDA-MB-231 HBC cell lines demonstrated a progressive increase in the 1.4 kb gadd45 transcript after exposure to 1 microM CD437. Western blot analysis showed increased gadd45 protein levels in MDA-MB-468 HBC cells following exposure to CD437. CD437 increased gadd45 mRNA levels by approximately 20-fold in MDA-MB-468 cells, however, the transcriptional activity was increased approximately 2-3-fold as demonstrated by the human gadd45 promoter-luciferase reporter construct and nuclear run-off assays. Sublines of MDA-MB-468 HBC cells expressing stably integrated GADD45 cDNA fragments were obtained and CD437-dependent induction of GADD45 analyzed. We report that approximately 300 nt located in the 5"-untranslated region (5"-UTR) of gadd45 mRNA are involved in the CD437-dependent 4-fold enhanced stability of gadd45 transcripts. MDA-MB-468 cells were stably transfected with either a plasmid having a CMV promoter-driven rabbit beta-globin gene or plasmids having a CMV promoter-driven chimeric gadd45 5"-UTR-rabbit beta-globin gene, where the entire gadd45 5"-UTR (from +1 to +298) or a 45 bp subfragment of the gadd45 5"-UTR (from +10 to +55) was positioned at the 5"-end of the rabbit beta-globin gene. CD437 was found to up-regulate expression of both the chimeric gadd45 -rabbit beta-globin transcripts, suggesting that cis element(s) involved in the CD437-dependent enhanced stability of gadd45 mRNA are contained in the 45 nt of the 5"-UTR of the gadd45 mRNA.

The objective of this study was to assess the expression of a multidrug resistance (MDR) phenotype, implicated in the cellular resistance of tumor to chemotherapy, in rheumatoid synovial membrane. Synovial membrane from 16 rheumatoid (RA) patients was studied. Six patients with osteoarthritis constituted the control group. The cell membrane expression of the glycoprotein Pgp 170, encoded by the MDR 1 gene, was determined by an immunoperoxidase technique using two different monoclonal antibodies (JSB 1, C 219). The polymerase chain reaction (PCR) methods were used in parallel to detect the presence of the MDR 1 gene mRNA in the synovial cells. Pgp 170 was expressed on the cell membrane of five RA patients and MDR 1 cellular transcription was detected in one other RA patient. We did not observe any association between synovial glycoprotein expression and age, disease activity, and a specific treatment with a long-acting drug. However, MDR protein expression was associated with the successive treatment with more than three disease-modifying antirheumatic drugs (DMARDs). We concluded that the synovial membrane expresses a glycoprotein recognized by the antibodies JSB 1 and C 219. The absence of concomitant MDR 1 transcription suggests the expression of an atypical MDR phenotype in the synovial membrane, distinct from the Pgp 170 encoded by the MDR 1 gene. The implications of the MDR phenotype and the resistance of RA to DMARDs is further discussed.