Negative regulation of YY1 transcription factor on the dynamin I gene promoter

The Yin and Yang of YY1 in the nervous system

The transcription factor Yin Yang 1 (YY1) is a multifunctional protein that can activate or repress gene expression depending on the cellular context. YY1 is ubiquitously expressed and highly conserved between species. However, its role varies in diverse cell types and includes proliferation, differentiation, and apoptosis. This review will focus on the function of YY1 in the nervous system including its role in neural development, neuronal function, developmental myelination, and neurological disease. The multiple functions of YY1 in distinct cell types are reviewed and the possible mechanisms underlying the cell specificity for these functions are discussed.

Cloning and expression analysis of YY1AP-related protein in the rat brain

YY1AP-related protein (YARP) is a structural homolog of YY1AP, a transcriptional coactivator of the multifunctional transcription factor YY1. We cloned a rat YARP cDNA that encoded a 2256 amino acid protein with 93% homology to the human counterpart. Northern blots revealed significant expression of the YARP gene in the rat brain. In situ hybridization demonstrated its expression in neurons throughout the brain, including pyramidal cells in the cerebral cortex and hippocampus and granule cells in the dentate gyrus. YARP was coexpressed with YY1 in these same neuronal cells. However, there was no evidence of YARP expression in glia. In the developing rat brain, the level of YARP mRNA ( approximately 10 kb) peaked at embryonic day 18 and promptly declined thereafter to reach the steady-state level found in adulthood, by 14 days after birth. These results suggest that YARP functions at a late stage of neurogenesis during perinatal development of the rat brain, as well as in mature neurons.

Multifunctional transcription factor YY1: a therapeutic target in human cancer?

The multifunctional transcription factor Yin Yang 1 (YY1) is a complex protein that has been shown to play pivotal roles in development, differentiation, cellular proliferation and apoptosis. It can act as a transcriptional repressor, an activator, or an initiator element binding protein that directs and initiates transcription of numerous cellular and viral genes. Because the expression and function of YY1 are known to be intimately associated with cell-cycle progression, the physiological significance of YY1 activity has recently been applied to models of cancer biology. Several lines of evidence imply that YY1 expression and/or activation is associated with tumourigenesis, in addition to its regulatory roles in normal biological processes. However, controversial results also raised and indicated that further studies are still needed to piece all of the seemingly contradictory data into a complete picture. On the basis of YY1 regulations and functions, novel drugs and specific treatment strategies may be developed with new therapeutic applications for tumour patients in the future.

Cloning and characterization of the rat Hsf2 promoter: a critical role of proximal E-box element and USF protein in Hsf2 regulation in different compartments of the brain

The complex patterns of tissue-, cell type- and developmental stage-specific expression of heat shock factor 2 (Hsf2) raise a question of how this can be achieved for this ubiquitous transcription factor. To explore molecular mechanisms responsible for the regulated expression of Hsf2, a 2638-bp 5'-flanking region of the rat Hsf2 gene was cloned and characterized. Since the brain represents one of the most complicated organs composed of several regions with different cell types, differential regulation of Hsf2 in various brain regions was investigated in detail. Results show that the major transcription initiation site of the Hsf2 gene is located at cytosine-155 relative to the translation initiation site. The E-box element located immediate upstream of the transcription initiation site was demonstrated to be critical for Hsf2 promoter activity, and the upstream stimulatory factor (USF) protein was identified as the major E-box binding protein. That the only two base exchange of the E-box core sequences from CACGTG to CACGGT severely impaired Hsf2 promoter activity and completely eliminated USF binding clearly demonstrated that the specific binding of USF to E-box is critical for Hsf2 promoter activity. Here we demonstrated that the Hsf2 expression levels varied significantly in different brain regions. We also demonstrated that Hsf2 expression levels in various brain regions relatively correlated with the E-box binding activity of USF. Based on these results, we suggest that E-box binding activity of USF protein may act as one of the major regulators of Hsf2 expression in situ although a possible involvement of other transcription factors cannot be ruled out. The presence of several transcription factor binding sites of biological importance in the Hsf2 promoter suggests that identifying the interplay of USF and these factors should help further elucidate the molecular mechanisms of tissue-, cell type- and developmental stage-specific expression of Hsf2.

Activation of dynamin I gene expression by Sp1 and Sp3 is required for neuronal differentiation of N1E-115 cells

Dynamin I is a key molecule required for the recycling of synaptic vesicles in neurons, and it has been known that dynamin I gene expression is induced during neuronal differentiation. Our previous studies established that neuronal restriction of dynamin I gene expression is controlled by Sp1 and nuclear factor-kappaB-like element-1. Here, using a series of deletion constructs and site-directed mutation, we found that transcription of dynamin I gene during neuronal differentiation of N1E-115 cells is controlled primarily by the Sp1 element located between -13 to -4 bp of the dynamin I promoter. Gel shift analysis demonstrated that in addition to Sp1, Sp3 could interact with this Sp1 element. The requirement for Sp family transcription factors in dynamin I gene expression was confirmed by using mithramycin, an inhibitor of Sp1/Sp3 binding. Mithramycin repressed dynamin I gene expression and resulted in blocking of neuronal differentiation of N1E-115 cells. The localization of the dynamin I protein was also restricted in the peripheral region of the nucleus by the mithramycin treatment. Thus, all of our results suggest that induction of dynamin I gene expression during N1E-115 cell differentiation is modulated by Sp1/Sp3 interactions with the dynamin I promoter, and its expression is important for neuronal differentiation of the N1E-115 cells.