Molecular Mechanism Involved in HIV-Tat Mediated inhibition of LPS-Induced IL-23 and IL-27 Production in Human Macrophages

Abstract

Monocyte-derived macrophages (MDMs) from HIV-infected patients and MDMs infected in vitro with HIV manifest inhibition of various cytokines including IL 12. Recently, IL-27 was shown to inhibit HIV replication in macrophages. Whether HIV infection or HIV regulatory proteins such as tat, impact IL-23 or IL-27 production in macrophages remains unknown. I have demonstrated that intracellular HIV-tat expression as well as HIV-tat basic domain peptides inhibited LPS-induced IL-23 and IL-27 proteins and their subunits in MDMs. First I investigated the signalling pathways involved in the regulation of LPS-induced IL-23 and IL-27 production in MDMs infected with control pLXIN retrovirus-infected MDMs. The p38 MAPK, SHP-1 and PI3K signalling molecules positively regulated LPS-induced IL-23 expression. In contrast, Src kinases and JNK MAPK negatively regulated LPS-induced IL-23 production. On the other hand, LPS-induced IL-27 production was positively regulated by the PI3K, p38 MAPKs and SHP-1 and Src kinases. Src kinases positively regulated LPS-induced IL-27 production whereas Src kinases and JNK negatively regulated LPS-induced IL-23 production. HIV-Tat significantly inhibited p38 MAPK and PI3K which were implicated in HIV-Tat-mediated inhibition of LPS-induced IL-23 and IL-27 production. Even though HIV-Tat inhibited ERK and JNK MAPK activation, these kinases were not involved in HIV-Tat-mediated inhibition of LPS-induced IL-23 and IL-27 production. While SHP-1 regulated LPS-induced IL-23 and IL-27 production, HIV-Tat did not inhibit SHP-1 and therefore were not involved in HIV-Tat-mediated inhibition of LPS-induced IL-23 and IL-27 production. HIV-Tat did not inhibit Src kinases and hence were not involved in HIV-Tat-mediated inhibition of LPS-induced IL-27 production. Furthermore, HIV-Tat did not inhibit the expression of upstream TLR4-activated signaling molecules including TRAF3, TRIF, MyD88, IRAK1, IRAK3, IRAK4, TRAF-1, TRAF-2, cIAP-1, cIAP-2 and, xIAP. These results suggest association of IL-23 and IL-27 inhibition by HIV with decreased HIV-specific immune responses, and increased viral replication. These results further suggest novel strategies to improve cellular immune responses and inhibition of HIV replication.