Immunotoxic mechanism of cannabinoid of cannabinoid compounds and 2-acetylaminofluorene

Abstract

2-acetylaminofluorene (AAF) have been established as being inhibitory on the lymphoproliferative response induced by lipopolysaccharide (LPS). We investigated the effects of AAF on protein kinase C (PKC) activation, an enzyme required for LPS-induced B-cell proliferation. PKC activity was studied in murine splenocytes by phosphorylation of PKC-specific substrate. The role of PKC as a positive signal in LPS-induced B-cell proliferation was confirmed by the observation that LPS increased the translocation of PKC to membrane and total PKC activity. In untreated splenocytes, approximately 70% of the total PKC activity was localized in the cytosol and 30% in the membrane fraction. Unexpectedly short-term treatment of AAF (10 min) to splenocytes culture significantly increased the membrane PKC activity while having little effect on total PKC activity. But, after treatment with 50 μM AAF for 18 hr, PKC activity in the cytosolic fraction decreased by 50% from control level, and splenocytes also lost 30% of total PKC activity. These results were confirmed by the observation that AAF also reduced the phosphorylation of the endogenous PKC-specific 80 kDa substrates. And, AAF was required in culture for ＞18 hr for maximum suppression of the LPS-induced B-cell proliferation, indicating that a sufficient time for depletion of PKC was need. Furthermore, as determined by the electrophoretic mobility shift assay (EMSA), AAF was shown to inhibit the binding activity of the transcription factor complex, NF-kB whose LPS-mediated induction in murine splenocytes is dependent on PKC activation. Also, a chloramphenicol acetyl transferase (CAT) expression vector containing multiple copies of the NF-κB element was transfected into pre-B cell line, 70Z/3 or mature B-cell line, S194 and CH12, and assessed induction of CAT activity. AAF treatment of the transfected 70Z/3 cell lines but not S194 and CH12 cell lines, resulted in a significant inhibition of CAT activity induced by LPS. These ...