Epitope spreading with an increase in the recognition of citrullinated antigens occurs before the onset of RA. Immunological differences in ACPA fine specificity between UA-UA patients and UA-RA patients are present at baseline and are associated with the future disease course.

Recently we described that genetic sequences in the immediately upstream region of the c‐fes/fps proto‐oncogene, designated fur, constituted a transcription unit for a 4.5‐kb mRNA. Here we present characteristics of the genetic organization of fur and some features of its putative translation product which we call furin. The nucleotide sequence of a 3.1‐kbp fur‐specific cDNA isolated from a human cDNA library revealed an open reading frame of 1,498 bp from which the 499 carboxy‐terminal amino acids of the primary fur translational product could be deduced. Computer analysis indicated that furin contained a possible transmembrane domain which resembled that of class II MHC antigens. Furthermore, a cysteine‐rich region was present. Significant homology, especially with respect to the topography of cysteine residues, was found between the cysteine‐rich regions of the human insulin receptor, the human epidermal growth factor receptor and furin. From the data presented here we deduce that fur may encode a membrane‐associated protein with a recognition function.

We have determined the complete nucleotide sequence of a human DNA fragment of approximately 13 kbp, which was shown by Southern blot analysis to contain the entire v‐fes/fps cellular homolog. The v‐fes/fps homologous sequences were dispersed over 11 kbp in 18 interspersed segments which were flanked by splice junctions. Fusion of these segments created a DNA fragment in which coding regions similar to those observed in the viral oncogenes v‐fes of the Gardner‐Arnstein (GA) and Snyder‐Theilen (ST) strains of feline sarcoma virus and v‐fps found in Fujinami sarcoma virus could be identified. A potential initiation site in the first exon was found. About 200 nucleotides downstream of a translational stop codon in the v‐fes/fps homologous region, a poly(A) addition signal was identified. The deduced amino acid sequence has a molecular weight of 93 390 dalton resembling NCP92, the recently described human c‐fes/fps product. The topography of human c‐fes/fps appeared to resemble that of chicken c‐fps.

Comparison of nucleotide sequence data of the 5' region of a fes/fps viral oncogene with those of the v-fes/fps homologous regions of man and cat revealed the position of the 3' portion of an as yet unidentified c-fes/fps exon. Comparative Southern blot and heteroduplex analysis of human and feline DNA immediately upstream of the v-fes/fps homologous regions showed extensive but discontinuous homology over a 9 kbp DNA stretch, which we have designated as fur. Northern blot analysis of mRNA from KG-1 myeloid cells with fes/fps- or fur-specific probes revealed a 3.0 kb fes/fps and a 4.5 kb fur transcript. Analysis of a number of tissues of an adult Wistar Lewis rat for the presence of fur transcripts revealed its differential expression pattern. An 0.95 kbp fes/fps-related and a 2.2 kbp fur-related cDNA recombinant clone were isolated from an oligo(dT)-primed KG-1 cDNA library. Comparative nucleotide sequence analysis of the fes/fps cDNA and its human genomic counterpart indicated that the cDNA contained genetic sequences that were identical to and colinear with exon 15-19 and, furthermore, that the poly(A) addition signal near the 3' end of exon 19 was functional. Similar analysis of the 2.2 kbp fur cDNA indicated that the poly(A) addition signal of the fur transcript was in close proximity of the newly discovered fes/fps exon. The region in between contained a CATT sequence but no 'TATA' box. The fur transcript was characterized by a long noncoding region at its 3' end.

The mammalian small heat shock protein aB-crystallin can be phosphorylated at three different sites, Ser19, Ser45 and Ser59. We compared the intracellular distribution of wildtype, nonphosphorylatable and all possible pseudophosphorylation mutants of aB-crystallin by immunoblot and immunocytochemical analyses of stable and transiently transfected cells. We observed that pseudophosphorylation at two (especially S19D/S45D) or all three (S19D/S45D/ S59D) sites induced the partial translocation of aB-crystallin from the detergent-soluble to the detergent-insoluble fraction. Double immunofluorescence studies showed that the pseudophosphorylation mutants localized in nuclear speckles containing the splicing factor SC35. The aB-crystallin mutants in these speckles were resistant to mild detergent treatment, and also to DNase I or RNase A digestion, indicating a stable interaction with one or more speckle proteins, not dependent on intact DNA or RNA. We further found that FBX4, an adaptor protein of the ubiquitin-protein isopeptide ligase SKP1/CUL1/F-box known to interact with pseudophosphorylated aB-crystallin, was also recruited to SC35 speckles when cotransfected with the pseudophosphorylation mutants. Because SC35 speckles also react with an antibody against aB-crystallin endogenously phosphorylated at Ser45, our findings suggest that aB-crystallin has a phosphorylation-dependent role in the ubiquitination of a component of SC35 speckles.