Figure 3.

Transcriptional cross-talk in the polyamine metabolic pathway. The expression levels of spermidine/spermine N¹-acetyltransferase (SAT1), spermine oxidase (SMOX), and ornithine decarboxylase (ODC) were compared in HEK293 cells that expressed either wild type (Wt) (HEK293-SAT1), inactive (HEK293-muSAT1), or an isoform of active/stable SAT1 with a greater enzymatic activity (HEK293-a/sSAT1) under the control of tetracycline-inducible promoter. Total RNA was extracted from tetracycline-induced (Tetracycline) and un-induced (control) cells at 24 h and subjected to northern blot analysis. Examination of SAT1, SMOX, and ODC mRNA levels indicated that the induction of enzymatically active SAT1 by tetracycline (lanes 1 and 3 from right) significantly enhances the expression of SMOX without impacting the expression of ODC. The expression of SMOX remained undetected in cells not treated with tetracycline (lanes 1 to 3 from left; also designated as control). The 28S and 18S rRNA (bottom) show comparable RNA loadings in the control and tetracycline-treated samples.