Modulating the Functional Contributions of c-Myc to the Human Endothelial Cell Cyclic Strain Response

Abstract

With each heartbeat, major arteries experience circumferential expansion due to internal pressure changes. This pulsatile force is called cyclic strain and has been implicated in playing a pivotal role in the genetic regulation of vascular physiology and pathology. This dissertation investigates the hypothesis that in human umbilical vein endothelial cells (HUVEC), pathological levels of cyclic strain activate the c-Myc promoter, leading to c-Myc transcription and downstream gene induction. To determine expression and time-dependency of c-Myc in HUVEC, mRNA and protein expression of c-Myc under physiological (6-10% cyclic strain) and pathological conditions (20% cyclic strain) were studied. Both c-Myc mRNA and protein expression increased more than three-fold in HUVEC (P4-P5) cyclically-strained at 20%. This expression occurred in a time-dependent manner, peaking in the 1.5-2 hour range and falling to basal levels by 3 hours. Subsequently, the mechanism of c-Myc transcription was investigated by using specific inhibitors to modulate c-Myc transcriptional activation. These compounds, obtained from the University of Arizona Cancer Center, attenuated cyclic-strain-induced c-Myc transcription by about 50%. Having established this reduction in expression, it was investigated how these effects modulate downstream genes that are regulated by c-Myc. The results indicate that direct targeting of the c-Myc promoter may decrease stretch-induced gene expression of vascular endothelial growth factor (VEGF), proliferating cell nuclear antigen (PCNA) and heat shock protein 60 (HSP60). These findings may help in the development of a novel therapeutic opportunity in vascular diseases.