Pyridine (PY) is present in coal tar, tobacco smoke, roasted coffee and creosote oil. PY inhalation has been reported to increase liver:body weight ratios in rats and to produce fatty degeneration of the liver; oral administration of PY to rats caused hepatic necrosis and the appearance of hepatic nodules. Research in our laboratories has shown PY to be a potent inducer of cytochromes P-450 in nasal, hepatic and renal tissues following inhalation exposure or i.p. administration. Western blot analysis shows P450IIE1 to be one of the major forms induced in these tissues and this form is the low KM PY N-oxidase. Preliminary data reveal no increase in hybridization P450IIE1 mRNA levels in total RNA isolated from hepatic tissues as evidence by Northern or dot blot analysis following PY treatment. In contrast, Northern or dot blot analysis reveals a rapid time-dependent loss of P450IIE1 poly (A)+ mRNA in hepatic tissue following PY treatment. This decrease in poly(A)+ mRNA is attributed to a loss of the poly(A)+ tail and is associated with early posttranscriptional events (increased translational efficiency) of P450IIE1 induction. Moreover, immunocytochemistry shows the presence of P450IIE1 in the nasal """"""""transition zone"""""""" and initial data suggest that PY may be per- oxisome proliferator. Thus, research is proposed to examine two hypotheses: (1) that P450IIE1 exhibits a unique substrate specificity in the oxidation of certain N and S atoms in xenobiotics, and (2) that PY induction of P450IIE1 occurs by posttranscriptional events, i.e. by increased translational efficiency which results in increased protein synthesis, whereas simultaneous induction of P450IIE1 and IA2 by PY is mediated by both transcriptional activation and posttranscriptional events. The specific objectives include: studies on the substrate specificity of P450IIE1 toward N- and S- containing xenobiotics, immunohistochemical studies on PY induction of P450 in nasal tissue including examination of P450IIE1, IA1 and IA2 mRNA in situ; and examination of the role of transcriptional and posttranscriptional regulation of P450IIE1, IA1 and IA2 in nasal, hepatic and renal tissue. Northern and dot blot analysis of mRNA and poly(A)+ mRNA, nuclear run-off assays, cell free translation of poly(A)+ mRNA, analysis of poly(A)+ tail length, mRNA ribosomal content, the levels of polysome-bound and free mRNA and the rate of P-450 protein synthesis in the presence and absence of cyclohexamide and actinomycin D following PY treatment will be accomplished with the goal of elucidating posttranscriptional regulatory pathways in the induction of P450s by PY.
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