ISOLATION AND FUNCTIONAL-CHARACTERIZATION OF CDNA OF SERUM-AMYLOID-A ACTIVATING FACTOR THAT BINDS TO THE SERUM-AMYLOID-A PROMOTER

Serum amyloid A (SAA), a plasma protein inducible in response to many inflammatory conditions, is associated with the pathogenesis of severa l diseases including reactive amyloidosis, rheumatoid arthritis, and a therosclerosis, We have previously reported an element of the SAA prom oter, designated SAA-activating sequence (SAS), that is involved in th e inflammation-induced SAA expression, and a nuclear factor, SAS-bindi ng factor (SAF), that interacts with the SAS element has been identifi ed previously (A. Ray and B. K. Ray, Mel. Cell. Biol, 16:1584-1594, 19 96), To evaluate how SAF is involved in SAA promoter activation, we ha ve investigated structural features and functional characteristics of this transcription factor. Our studies indicate that SAF belongs to a family of transcription factors characterized by the presence of multi ple zinc finger motifs of the Cys(2)-His(2) type at the carboxyl end. Of the three cloned SAF cDNAs (SAF-1, SAF-5, and SAF-8), SAF-1 isoform showed a high degree of homology to MAZ/ZF87/Pur-1 protein while SAF- 5 and SAF-8 isoforms are unique and are related to SAF-1/MAZ/ZF87/Pur- 1 at the zinc finger domains but different elsewhere, Although structu rally distinct, all members are capable of activating SAS element-medi ated expression and display virtually identical sequence specificities . However, varying levels of expression of members of this gene family were observed in different tissues, Functional activity of SAF is reg ulated by a posttranslational event as SAF DNA-binding and transactiva tion abilities are increased by a protein phosphatase inhibitor, okada ic acid, and inhibited by a protein kinase inhibitor, H7. Consistent w ith this observation, increased DNA binding of the cloned SAF and its hyperphosphorylation, in response to okadaic acid treatment of the tra nsfected cells, were observed. Taken together, our results suggest tha t, in addition to tissue-specific expression, SAFs, a family of zinc f inger transcription factors, undergo a modification by a posttranslati onal event that confers their SAA promoter-binding activity and transa ctivation potential.