Nicotinamide phosphoribosyl transferase coordinates stabilization of plasminogen activator inhibitor‐1 mRNA at the myoendothelial junction

Abstract

We previously demonstrated that plasminogen activator inhibitor‐1 (PAI‐1) regulates MEJ formation in response to obese conditions. Using TNF‐α to mimic obese conditions, we have shown that PAI‐1 mRNA is stabilized at the myoendothelial junction (MEJ), resulting in increased PAI‐1 protein. How PAI‐1 mRNA is stabilized at the MEJ is unknown. To elucidate this mechanism we show that serpine binding protein‐1 (SERBP1), which stabilizes PAI‐1 mRNA, and nicotinamide phosphoribosyl transferase (NAMPT), which contains a microtubule binding domain (MBD), both increase at the MEJ in response to TNF‐α. We then demonstrate via co‐immunoprecitation an interaction between these two proteins that is enhanced by TNF‐α. Next, using a microtubule binding assay we show that NAMPT can bind microtubules in a dose‐dependent manner, independent of microtubule length. This suggests that SERPB1 and NAMPT may act as a PAI‐1 RNA binding protein (RBP) complex at the MEJ. To determine the importance of the NAMPT MBD for increases in PAI‐1 at the MEJ, we designed a peptide with a TAT‐tag, targeted to the MBD of NAMPT. Treatment with the MBD peptide negated the effects of TNF‐α on PAI‐1 at the MEJ, while a scrambled peptide had no effect. Together, these data indicate that during obesity, stabilization of PAI‐1 mRNA occurs via a PAI‐1 RBP complex that is anchored by NAMPT to microtubules at the MEJ, promoting local increases in PAI‐1 protein.