Increased frequency of complement C4B deficiency in rheumatoid arthritis.

OBJECTIVE: To assess the copy number variation of complement C4A and C4B genes in patients with rheumatoid arthritis (RA). METHODS: DNA samples were obtained from 299 patients and controls and analyzed for copy number variation of total complement C4, C4A, and C4B genes. The results were compared by chi-square analysis, and odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated. RESULTS: Chi-square analysis revealed similar distribution patterns of total C4 alleles in RA patients (n = 160), non-RA patients (n = 88), and healthy controls (n = 51). There was no trend toward C4A deficiency as in lupus. Significant differences in C4B distribution were observed in RA patients, in whom an ∼2-fold increase in the frequency of homozygous and/or heterozygous C4B deficiency (0 or 1 allele) (40%) was present relative to non-RA patients or healthy controls (both 21.6%). C4B deficiency was more frequent in seropositive RA patients than in seronegative RA patients (44% versus 31%). The odds of C4B deficiency were 2.99 (95% CI 1.58-5.65) (P = 0.0006) in seropositive RA patients relative to non-RA controls. These findings were confirmed in a larger healthy control cohort, yielding an OR of 1.83 (95% CI 1.21-2.76) (P = 0.0056). The association of the shared epitope with C4B deficiency was significantly greater in seropositive RA patients than in non-seropositive RA controls (96% versus 54.5%) (P < 0.0001), suggesting that C4B deficiency interacts with the shared epitope in the development of seropositive RA. CONCLUSION: Our findings indicate a relationship between C4B copy number variation and RA that approximates that seen between C4A copy number variation and lupus. The concurrence of C4B deficiency and the shared epitope in seropositive RA may have broad implications for our understanding of RA pathogenesis.

A flexible approach to studying post-transcriptional gene regulation in stably transfected mammalian cells.

The study of post-transcriptional regulation is constrained by the technical limitations associated with both transient and stable transfection of chimeric reporter plasmids examining the activity of 3'-UTR cis-acting elements. We report the adaptation of a commercially available system that enables consistent stable integration of chimeric reporter cDNA into a single genomic site in which transcription is induced by tetracycline. Using this system, we demonstrate the tight control afforded by this system and its suitability in mapping the regulatory function of defined cis-acting elements in the human TNF 3'-UTR, as well as the distinct effects of serum starvation on transiently transfected and stably integrated chimeric reporter genes.

Separate cis-trans pathways post-transcriptionally regulate murine CD154 (CD40 ligand) expression: a novel function for CA repeats in the 3'-untranslated region.

We report a role for CA repeats in the 3'-untranslated region (3'-UTR) in regulating CD154 expression. Human CD154 is encoded by an unstable mRNA; this instability is conferred in cis by a portion of its 3'-UTR that includes a polypyrimidine-rich region and CA dinucleotide repeat. We demonstrate similar instability activity with the murine CD154 3'-UTR. This instability element mapped solely to a conserved 100-base CU-rich region alone, which we call a CU-rich response element. Surprisingly, the CA dinucleotide-rich region also regulated reporter expression but at the level of translation. This activity was associated with poly(A) tail shortening and regulated by heterogeneous nuclear ribonucleoprotein L levels. We conclude that the CD154 3'-UTR contains dual cis-acting elements, one of which defines a novel function for exonic CA dinucleotide repeats. These findings suggest a mechanism for the association of 3'-UTR CA-rich response element polymorphisms with CD154 overexpression and the subsequent risk of autoimmune disease.