Upstream Stimulatory Factor (USF) and CCAAT/Enhancer Binding Protein δ (C/EBPδ) Compete for overlapping Sites in the Negative Regulatory Region of the HIV-1 LTR

Human immunodeficiency virus type 1 (HIV-1) is a human retrovirus and the causative agent of the acquired immunodeficiency syndrome. Genetic analysis has revealed that the HIV-1 LTR contains a potential negative regulatory element (NRE) with an E box, the recognition sequence for the helix-loop-helix (HLH) family of transcription factors. Furthermore, the upstream stimulatory factor (USF) has been implicated as a negative regulator of HIV-1 expression. Here, we report that the NRE is a composite element and that both C/EBPδ and USF can specifically bind to the NRE. The recognition sequence for C/EBPδ overlaps with the E box in the NRE of HIV-1. Competition experiments showed that either USF or C/EBPδ binds to this NRE but not both together

Electrical signals affect the cardiomyocyte transcriptome independently of contraction

Martherus RS, Vanherle SJ, Timmer ED, Zeijlemaker VA, Broers JL, Smeets HJ, Geraedts JP, Ayoubi TA. Electrical signals affect the cardiomyocyte transcriptome independently of contraction. Physiol Genomics 42A: 283-289, 2010. First published September 21, 2010; doi:10.1152/physiolgenomics.00182.2009.-Cardiomyocytes in vivo are continuously subjected to electrical signals that evoke contractions and instigate drastic changes in the cells' morphology and function. Studies on how electrical stimulation affects the cardiac transcriptome have remained limited to a small number of heart-specific genes. Furthermore, these studies have ignored the interplay between the electrical excitation and the subsequent contractions. We carried out a genomewide assessment of the effects of electrical signaling on gene expression, while distinguishing between the effects deriving from the electrical pulses themselves and the effects instigated by the evoked contractions. Changes in gene expression in primary cultures of neonatal ventricular cardiomyocytes from Lewis Rattus norvegicus were investigated with microarrays and RT-quantitative PCR (QPCR). A series of experiments was included in which the culture medium was supplemented with the contraction inhibitor blebbistatin to allow for electrical stimulation in the absence of contraction. Electrical stimulation was shown to directly enhance calcium handling and induce cardiomyocyte differentiation by arresting cell division and activating key cardiac transcription factors as well as additional differentiation mechanisms such as wnt signaling. Several genes involved in metabolism were also directly activated by electrical stimulation. Furthermore, our data suggest that contraction exerts negative feedback on the transcription of various genes. Together, these observations indicate that intercellular electric currents between adjacent cardiomyocytes have an important role in cardiomyocyte development. They act at least partially through a pulse-specific gene expression program that is activated independently from the evoked contractions