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Background-Recent studies have identified critical roles for microRNAs (miRNAs) in a variety of cellular processes, including regulation of cardiomyocyte death. However, the signature of miRNA expression and possible roles of miRNA in the ischemic heart have been less well studied. Methods and Results-We performed miRNA arrays to detect the expression pattern of miRNAs in murine hearts subjected to ischemia/reperfusion (I/R) in vivo and ex vivo. Surprisingly, we found that only miR-320 expression was significantly decreased in the hearts on I/R in vivo and ex vivo. This was further confirmed by TaqMan real-time polymerase chain reaction. Gain-of-function and loss-of-function approaches were employed in cultured adult rat cardiomyocytes to investigate the functional roles of miR-320. Overexpression of miR-320 enhanced cardiomyocyte death and apoptosis, whereas knockdown was cytoprotective, on simulated I/R. Furthermore, transgenic mice with cardiac-specific overexpression of miR-320 revealed an increased extent of apoptosis and infarction size in the hearts on I/R in vivo and ex vivo relative to the wild-type controls. Conversely, in vivo treatment with antagomir-320 reduced infarction size relative to the administration of mutant antagomir-320 and saline controls. Using TargetScan software and proteomic analysis, we identified heat-shock protein 20 (Hsp20), a known cardioprotective protein, as an important candidate target for miR-320. This was validated experimentally by utilizing a luciferase/GFP reporter activity assay and examining the expression of Hsp20 on miR-320 overexpression and knockdown in cardiomyocytes. Conclusions-Our data demonstrate that miR-320 is involved in the regulation of I/R-induced cardiac injury and dysfunction via antithetical regulation of Hsp20. Thus, miR-320 may constitute a new therapeutic target for ischemic heart diseases. Key Words: apoptosis Ⅲ ischemia Ⅲ microRNA Ⅲ myocardial infarction Ⅲ reperfusion M ore than 1 million Americans suffer from myocardial infarction every year. 1 Both human autopsy data and evidence from rodent models of myocardial infarction indicate that most cell death happens by apoptosis during the initial 2 to 4 hours after coronary occlusion. 2,3 Clinical treatment of myocardial infarction by thrombolytic therapy and revascularization by percutaneous coronary intervention or coronary artery bypass graft surgery are effective. 1,3 However, given the health, economic, and personal burden caused by ischemic heart disease, research into additional treatment modalities is imperative. Furthermore, the molecular mechanisms that regulate gene expression during myocardial ischemia/reperfusion (I/R) are still not completely understood. Clinical Perspective on p 2366MicroRNAs (miRNAs) are a class of endogenous nonprotein-coding RNAs comprising Ϸ22 nucleotides. 4 -6 They regulate gene expression via RNA-induced silencing complexes, targeting them to mRNAs where they inhibit translation or direct destructive cleavage. 4 -6 Increasing evidence indicates the importa...

Tumor hypoxia reduces the effectiveness of radiation therapy by limiting the biologically effective dose. An acute increase in tumor oxygenation before radiation treatment should therefore significantly improve the tumor cell kill after radiation. Efforts to increase oxygen delivery to the tumor have not shown positive clinical results. Here we show that targeting mitochondrial respiration results in a significant reduction of the tumor cells' demand for oxygen, leading to increased tumor oxygenation and radiation response. We identified an activity of the FDA-approved drug papaverine as an inhibitor of mitochondrial complex I. We also provide genetic evidence that papaverine's complex I inhibition is directly responsible for increased oxygenation and enhanced radiation response. Furthermore, we describe derivatives of papaverine that have the potential to become clinical radiosensitizers with potentially fewer side effects. Importantly, this radiosensitizing strategy will not sensitize well-oxygenated normal tissue, thereby increasing the therapeutic index of radiotherapy.

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Kru¨ppel-like factor 2 (KLF2) is a member of the KLF family of zinc-finger transcription factors and is involved in maintaining T-cell quiescence, regulating preadipocyte differentiation, endothelial cell function and lung development. We used a tetracycline-inducible system in Jurkat T leukemia cells to study the biological role of KLF2 in cellular growth and differentiation. Our results show that expression of KLF2 inhibits cell growth in autonomously proliferating Jurkat cells. Further, 3 H-thymidine uptake assays indicate that KLF2 inhibits DNA synthesis in these cells. Moreover, both activation and inhibitory domains are required for KLF2 to suppress Jurkat cell proliferation. In addition, KLF2 upregulates p21 WAF1/CIP1 expression. Additionally, we found that KLF2 upregulates p21 WAF1/CIP1 promoter activity in Jurkat, HepG2 and SW480 cells. Our analysis shows that the potential KLF2 responsive elements are located between À124 and À60 of the p21 WAF1/CIP1 promoter. The sole CACCC site, a sequence recognized by KLF2, in this region is not the element responsive to KLF2. Finally, we determined that the Sp1-3-binding site is the functional responsive element of KLF2 in the p21 WAF1/CIP1 promoter, and we conclude that KLF2 directly regulates p21 WAF1/CIP1 expression.

Gene targeting of a member of small leucine-rich repeat proteoglycans demonstrates that collagen fibrillogenesis is mediated by a set of extracellular matrix components, which interact with collagen. Collagen-associated protein dermatopontin knockout mice were generated in order to analyze the biologic involvement of dermatopontin in the formation of collagen fibrils. Although dermatopontin-null mice did not exhibit any obvious anatomical abnormality, skin elasticity was increased. Skin tensile tests revealed that the initial elastic modulus was 57% lower in dermatopontin-null mice than in wild-type mice, and that maximum tensile strength was similar. Remarkably, light microscopy study showed a significant decrease in the relative thickness of the dermis in dermatopontin-null mice compared with wild-type mice (45.2 +/- 3.09% and 57.8 +/- 4.25%, respectively). The skin collagen content was 40% lower in dermatopontin-null than in wild-type mice. Collagen fibrils in dermatopontin-null mice showed a great variety in diameter and irregular contours under the electron microscope. These data indicate that dermatopontin plays a critical role in elasticity of skin and collagen accumulation attributed to collagen fibrillogenesis in vivo.

Regulation of diurnal and circadian rhythms and cell proliferation are coupled in all mammals, including humans. However, the molecular mechanisms by which diurnal and circadian rhythms regulate cell proliferation are relatively poorly understood. In this study, we report that tumor growth in nude rats bearing human steroid receptor-negative MCF-7 breast tumors can be significantly accelerated by exposing the rats to light at night (LAN). Under normal conditions of an alternating light/dark cycle, proliferating cell nuclear antigen (PCNA) levels in tumors were maximal in the early light phase but remained at very low levels throughout the daily 24-hour cycle period monitored. Surprisingly, PCNA was expressed in tumors continually at a high level throughout the entire 24-hour period in LAN-exposed nude rats. Daily fluctuations of Akt and mitogen activated protein kinase activation in tumors were also disrupted by LAN. These fluctuations did not track with PCNA changes, but we found that activation of the Akt stimulatory kinase phosphoinositide-dependent protein kinase 1 (PDK1) directly correlated with PCNA levels. Expression of insulin-like growth factor 1 receptor (IGF-1R), an upstream signaling molecule for PDK1, also correlated with fluctuations of PDK1/PCNA in the LAN group. In addition, circulating IGF-1 concentrations were elevated in LAN-exposed tumor-bearing nude rats. Finally, RNAimediated knockdown of PDK1 led to a reduction in PCNA expression and cell proliferation in vitro and tumor growth in vivo, indicating that PDK1 regulates breast cancer growth in a manner correlated with PCNA expression. Taken together, our findings demonstrate that LAN exposure can accelerate tumor growth in vivo, in part through continuous activation of IGF-1R/PDK1 signaling. Cancer Res; 71(7); 2622-31. Ó2011 AACR.

This migration defect is also observed when platelet-derived growth factor-B (PDGF) controlled migration is studied in murine embryonic fibroblast (MEF) cells from KLF2؊/؊ animals. In addition, KLF2 ؊/؊ MEFs exhibit a significant growth defect, indicating that KLF2 is required to maintain the viability of MEF cells. The PDGF signal is mediated through the Src signaling pathway, and a downstream target of KLF2 is sphingosine 1-phosphate receptor 1. These studies demonstrate that KLF2 is required for smooth muscle cell migration and elucidate a novel mechanism involving communication between PDGF and KLF2 in vascular maturation.