Monocytes/macrophages are vital for host-immune responses and have been implicated in the pathogenesis of rheumatoid arthritis (RA).  We demonstrated that PI3K/Akt-l-dependent Mcl-1 expression is vital for macrophage survival.  Suppression of PI3K/Akt reduced Mcl-1 expression, resulting in apoptosis mediated through the mitochondrial pathway.  Forced downregulation of Mcl-1 through antisense oligonucleotides also induced apoptosis, demonstrating that Mcl-1 is essential for macrophage viability.  Further, our preliminary data suggested that Mcl-1 may also be regulated by the JAK/STAT pathway in human macrophages.  Therefore, we propose to determine the mechanisms by which the PI3K/Akt and JAK/STAT3 pathways contribute to the regulation of Mcl-1 in macrophages.  Additionally, we will identify the mechanism by which Mcl-1 protects macrophages by examining the interaction of Mcl-1 with pro-apoptotic molecules, such as Bax in macrophages to delineate the mechanism of mitochondrial dysfunction that occurs following Mcl-1 ablation.  Our preliminary data suggests that Mcl-1 may be important in the in maintaining the viability of RA synovial macrophages.  Additionally, our preliminary data has revealed that in vitro, Mcl-1 was highly expressed in RA, compared to osteoarthritis (OA), synovial fibroblasts.  Mcl-1 was also strongly expressed in the synovium of rats with adjuvant-induced arthritis (AIA).  Therefore, we propose to characterize the expression and function of Mcl-1 in the RA joint, examining macrophages and synovial fibroblasts.  We propose to determine if the forced downregulation of Mcl-1 will ameliorate experimental arthritis, which would indicate that Mcl-1 is a contributor to the initiation and/or progression of arthritis.  Thus, this proposal will delineate the mechanisms regulating the expression and the novel functions of Mcl-1 in macrophages.  Further studies are proposed to delineate potential cell type-specific differences between macrophages and normal, osteoarthritis and rheumatoid arthritis synovial fibroblasts.  These experiments will provide new and important information concerning the novel role of Mcl-1, which may provide insights that will lead to the development of improved therapy for patients with RA.  PERFORMANCESITE(S) (organization,city, state) Northwestern University Medical School Department of Medicine, Division of Rheumatology 303 E Chicago Ave Ward 3-315 Chicago, IL 60611 KEY PERSONNEL.  See instructions. Usecontinuation pages as needed toprovidetherequiredinformationintheformatshownbelow.  StartwithPrincipalInvestigatorL[unreadable] istallotherkeypersonnelinalphabeticaol rder,lastnamefirst.  Name Organization Roleon Project Richard M. Pope, MD Northwestern University PI Hongtao Liu, MD PhD Northwestern University Co-investigator Harris Perlman, PhD Northwestern University Co-investigator G. Kenneth Haines, MD Northwestern University Co-investigator Disclosure Permission Statement.  Applicableto SBIR/STTROnly.  See instructions.[]  Yes [_ No [unreadable] PHS 398 (Rev. 05/01) Page2 Form Page 2. [ unreadable] Principal InvestigatodProgram Director (Last, first, middle): Pope, Richard, M The name of the principal investigator/program director must be provided at the top of each printed page and each continuation page.  RESEARCH GRANT TABLE OF CONTENTS Page Numbers Face Page.................................................................................................................................................. 1 Description,