Abstract
Despite significant progress, the molecular mechanisms responsible for pancreatic beta cell depletion and development of diabetes remain poorly defined. At present, there is no preventive measure against diabetes. The positive impact of CXCL12 expression on the pancreatic beta cell prosurvival phenotype initiated this study. Our aim was to provide novel insight into the regulation of rat CXCL12 gene (Cxcl12) transcription. The roles of poly(ADP-ribose) polymerase-1 (PARP-1) and transcription factor Yin Yang 1 (YY1) in Cxcl12 transcription were studied by examining their in vitro and in vivo binding affinities for the Cxcl12 promoter in a pancreatic beta cell line by the electrophoretic mobility shift assay and chromatin immunoprecipitation. The regulatory activities of PARP-1 and YY1 were assessed in transfection experiments using a reporter vector with a Cxcl12 promoter sequence driving luciferase gene expression. Experimental evidence for PARP-1 and YY1 revealed their trans-acting potential, wherein PARP-1 displayed an inhibitory, and YY1 a strong activating effect on Cxcl12 transcription. Streptozotocin (STZ)-induced general toxicity in pancreatic beta cells was followed by changes in Cxcl12 promoter regulation. PARP-1 binding to the Cxcl12 promoter during basal and in STZ-compromised conditions led us to conclude that PARP-1 regulates constitutive Cxcl12 expression. During the early stage of oxidative stress, YY1 exhibited less affinity toward the Cxcl12 promoter while PARP-1 displayed strong binding. These interactions were accompanied by Cxcl12 downregulation. In the later stages of oxidative stress and intensive pancreatic beta cell injury, YY1 was highly expressed and firmly bound to Cxcl12 promoter in contrast to PARP-1. These interactions resulted in higher Cxcl12 expression. The observed ability of PARP-1 to downregulate, and of YY1 to upregulate Cxcl12 promoter activity anticipates corresponding effects in the natural context where the functional interplay of these proteins could finely balance Cxcl12 transcription.
Highlights
Type 1 diabetes (T1D) is a multifactorial disease believed to be of immunological origin, precipitated by infections and environmental factors in genetically predisposed individuals
CXCL12 is proven to be important in pancreatic islet survival, we aimed to advance knowledge concerning the regulation of rat CXCL12 gene (Cxcl12) transcription, and for the first time we focused on two transcription factors; the poly(ADP-ribose) polymerase-1 (PARP-1) and the ubiquitous transcription factor Yin Yang 1 (YY1)
RT-qPCR analysis of the rat and human genes encoding for CXCL12 revealed no significant differences in rat Cxcl12 expression between wt and clone #1 cells while high expression of human Cxcl12 was observed in clone #1 cells, confirming its stable genomic integration (Fig. 1B)
Summary
Type 1 diabetes (T1D) is a multifactorial disease believed to be of immunological origin, precipitated by infections and environmental factors in genetically predisposed individuals. The hallmark of T1D is selective death of pancreatic insulinproducing beta cells resulting from attack by mononuclear cells. The maintenance of an appropriate number of pancreatic beta cells remains a viable interventive measure in diabetes. The chemokine (C-X-C motif) ligand 12 (CXCL12) or stromal cell-derived factor-1 (SDF-1) belongs to the CXC group of chemokines. CXCL12 was discovered as a pre-B cell growthstimulating factor [1,2]. The CXCL12 is a ligand of two transmembrane receptors, chemokine (C-X-C motif) receptor 4 (CXCR4) and chemokine (C-X-C motif) receptor 7 (CXCR7) [3,4]. An antidiabetogenic potential of CXCL12 was recently revealed in vitro and in vivo. Transgenic mice that overexpress CXCL12 in their beta cells are resistant to apoptosis and diabetes
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