CLIF, a Novel Cycle-like Factor, Regulates the Circadian Oscillation of Plasminogen Activator Inhibitor-1 Gene Expression

Abstract

The onset of myocardial infarction occurs frequently in the early morning, and it may partly result from circadian variation of fibrinolytic activity. Plasminogen activator inhibitor-1 activity shows a circadian oscillation and may account for the morning onset of myocardial infarction. However, the molecular mechanisms regulating this circadian oscillation remain unknown. Recent evidence indicates that basic helix-loop-helix (bHLH)/PAS domain transcription factors play a crucial role in controlling the biological clock that controls circadian rhythm. We isolated a novel bHLH/PAS protein, cycle-like factor (CLIF) from human umbilical vein endothelial cells. CLIF shares high homology with Drosophila CYCLE, one of the essential transcriptional regulators of circadian rhythm. CLIF is expressed in endothelial cells and neurons in the brain, including the suprachiasmatic nucleus, the center of the circadian clock. In endothelial cells, CLIF forms a heterodimer with CLOCK and up-regulates the PAI-1 gene through E-box sites. Furthermore, Period2 and Cryptochrome1, whose expression show a circadian oscillation in peripheral tissues, inhibit the PAI-1 promoter activation by the CLOCK:CLIF heterodimer. These results suggest that CLIF regulates the circadian oscillation of PAI-1 gene expression in endothelial cells. In addition, the results potentially provide a molecular basis for the morning onset of myocardial infarction.

Involvement of circadian clock gene Clock in diabetes‐induced circadian augmentation of plasminogen activator inhibitor‐1 (PAI‐1) expression in the mouse heart

“…2A). However, rhythmic PAI-1 mRNA expression was damped in the hearts of control Clock mutant mice (F [3,16] Plasma levels of total PAI-1 antigen were obviously increased by STZ in both WT and Clock mutant mice (F[1,32] = 45.1, P < 0.01 and F[1,33] = 23.8, P < 0.01, respectively) (Fig. 3).…”

“…Maemura et al [3] described the circadian expression of PAI-1 mRNA in the heart and kidneys of mice, and suggested that the circadian oscillation of PAI-1 gene expression plays an important role in the circadian fluctuation of blood fibrinolytic activity. Assays in vitro have shown that CLOCK:BMAL2 (CLIF) and CLOCK:-BMAL1 heterodimers up-regulate human PAI-1 gene expression via E-box (CACGTG) elements located at bp À677 to À672 and at bp À562 to À557 [3].…”

“…Levels of blood plasminogen activator inhibitor-1 (PAI-1), the primary physiological inhibitor of plasminogen activators, peak during the early morning, which might explain the morning onset of myocardial infarctions [1,2]. Maemura et al [3] described the circadian expression of PAI-1 mRNA in the heart and kidneys of mice, and suggested that the circadian oscillation of PAI-1 gene expression plays an important role in the circadian fluctuation of blood fibrinolytic activity. Assays in vitro have shown that CLOCK:BMAL2 (CLIF) and CLOCK:-BMAL1 heterodimers up-regulate human PAI-1 gene expression via E-box (CACGTG) elements located at bp À677 to À672 and at bp À562 to À557 [3].…”

Night-time restricted feeding normalises clock genes and Pai-1 gene expression in the db/db mouse liver

“…An increase in blood glucose, insulin and triglyceride levels produces Pai-1 mRNA expression in the liver [30], and insulin and triglycerides synergistically induce Pai-1 biosynthesis in hepatocytes [30]. Previously published data suggest that the CLOCK:BMAL2 (or BMAL1) heterodimer may be responsible for regulating mPai-1 circadian expression [6]. All of these factors together may cause a constant high level of mPai-1 gene expression in the liver of db/db mice.…”

“…Recent study shows that mammalian peripheral tissues contain an oscillator that couples to a central oscillator under normal conditions [3], and the clock genes in these peripheral tissues show clear circadian rhythms [4]. Plasminogen activator inhibitor type 1 (PAI-1), a primary regulator of the fibrinolytic cascade, has two functional E-box motifs in the promoter [5], and its gene expression is regulated by the circadian clock [6].…”