A mammalian multigene family, the serum amyloid A (SAA) gene family, is differentially regulated during inflammation. There are three functional genes in this family -- SAA1, 2, and 3 -- and a structurally related pseudogene. Upon induction, the level of SAA mRNA in the liver and the concentration of SAA in plasma can increase as much as 1,000- fold. Though we know that SAA expression is regulated during inflammation, at least in part, by the circulating inflammatory cytokine interleukin-1 (IL-1) and that NFkappaB- and C/EBP-related transcription factors are important for its expression, we know few molecular details about its differential regulation and tissue-specific expression during inflammation and the precise roles of these transcription factors. The diverse features of this differential expression during inflammation, together with the differential response by members of the SAA gene family in different tissues, make the SAA gene family a particularly informative model to examine the molecular mechanism underlying the complexity of gene control. The overall objective of our research program is to understand the molecular mechanisms involved in the transcriptional regulation of SAA genes. We hypothesize that multiple regulatory mechanisms, including induction and repression mechanisms, are likely to exist in order to establish the appropriate physiological levels of SAA during inflammation. Furthermore, these mechanisms must involve regulatory DNA sequences and their interactions with sequence- specific trans-regulatory factors. Our studies on the SAA genes support these hypotheses and have identified both positive and negative regulatory elements and their corresponding sequence-specific binding proteins. Given the unique opportunity to study the differential regulation of the SAA genes, we will also focus our studies on the comparisons of these genes. Such studies have the potential to generate new insights into the molecular evolution of regulatory mechanisms elicited by inflammatory cytokines and tissue-specific control and may in turn lead to increased understanding of inflammatory processes and ways to modulate them.
The Specific Aims for our studies are: 1). To develop an in vitro transcription system which demonstrates inducible, cell-type specific transcription following stimulation; 2.) To examine the molecular basis of differential regulation of SAA1 and SAA3 genes; 3.) To characterize and purify tissue-specific repressor and to clone its cDNA; 4.) To examine the involvement of C/EBP family proteins in SAA gene regulation.
