Functional Assessment of Clubfoot Associated HOXA9, TPM1, and TPM2 Variants Suggests a Potential Gene Regulation Mechanism.

Background: Isolated nonsyndromic clubfoot is a common birth defect affecting 135,000 newborns worldwide each year. Although treatment has improved, substantial long-term morbidity persists. Genetic causes have been implicated in family-based studies but the genetic changes have eluded identification.

The human GFI136N variant induces epigenetic changes at the Hoxa9 locus and accelerates K-RAS driven myeloproliferative disorder in mice.

The coding single nucleotide polymorphism GFI136N in the human gene growth factor independence 1 (GFI1) is present in 3%-7% of whites and increases the risk for acute myeloid leukemia (AML) by 60%. We show here that GFI136N, in contrast to GFI136S, lacks the ability to bind to the Gfi1 target gene that encodes the leukemia-associated transcription factor Hoxa9 and fails to initiate histone modifications that regulate HoxA9 expression. Consistent with this, AML patients heterozygous for the GFI136N variant show increased HOXA9 expression compared with normal controls.

Stress-induced phosphorylation of PACT reduces its interaction with TRBP and leads to PKR activation.

PACT is a stress-modulated activator of interferon (IFN)-induced double-stranded (ds) RNA-activated protein kinase (PKR) and is an important regulator of PKR-dependent signaling pathways. Stress-induced phosphorylation of PACT is essential for PACT's association with PKR leading to PKR activation. PKR activation by PACT leads to phosphorylation of translation initiation factor eIF2α, inhibition of protein synthesis, and apoptosis.

Essential role of PACT-mediated PKR activation in tunicamycin-induced apoptosis.

Cellular stresses such as disruption of calcium homeostasis, inhibition of protein glycosylation, and reduction of disulfide bonds result in accumulation of misfolded proteins in the endoplasmic reticulum (ER) and lead to cell death by apoptosis. Tunicamycin, which is an inhibitor of protein glycosylation, induces ER stress and apoptosis. In this study, we examined the involvement of double-stranded RNA (dsRNA)-activated protein kinase (PKR) and its protein activator PACT in tunicamycin-induced apoptosis.

Interaction of human tRNA-dihydrouridine synthase-2 with interferon-induced protein kinase PKR.

PKR is an interferon (IFN)-induced protein kinase, which is involved in regulation of antiviral innate immunity, stress signaling, cell proliferation and programmed cell death. Although a low amount of PKR is expressed ubiquitously in all cell types in the absence of IFNs, PKR expression is induced at transcriptional level by IFN. PKR's enzymatic activity is activated by its binding to one of its activators.

Differential regulation of HOXA9 expression by nuclear factor kappa B (NF-kappaB) and HOXA9.

HOXA9 is a homeobox transcription factor expressed in endothelial cells (EC) and its expression is rapidly downregulated during EC activation by inflammatory signals like tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS). Recently, we have shown that HOXA9 overexpression prevents EC activation by inhibiting NF-kappaB activity, which suggests that HOXA9 downregulation is an essential event for EC activation. The present study is directed towards understanding the mechanism of HOXA9 regulation during EC activation.

Homeobox gene HOXA9 inhibits nuclear factor-kappa B dependent activation of endothelium.

Cytokine-induced expression of adhesion molecules such as ICAM-1, VCAM-1, and E-selectin, on activated endothelial cells (EC) plays an essential role in the development of inflammatory diseases like atherosclerosis. Transcription factor nuclear factor-kappa B (NF-kappaB) is mainly responsible for the induced expression of these adhesion molecules in response to pro-inflammatory cytokines. The mechanisms that maintain EC in a "basal" state and negatively regulate EC activation remain to be characterized.

Regulation of vascular smooth muscle proliferation by heparin: inhibition of cyclin-dependent kinase 2 activity by p27(kip1).

Uncontrolled proliferation of vascular smooth muscle cells (VSMCs) contribute to intimal hyperplasia during atherosclerosis and restenosis. Heparin is an antiproliferative agent for VSMCs and has been shown to block VSMC proliferation both in tissue culture systems and in animals. Despite the well documented antiproliferative actions of heparin, its cellular targets largely remain unknown.

Contribution of double-stranded RNA-activated protein kinase toward antiproliferative actions of heparin on vascular smooth muscle cells.

Objective: The proliferation of vascular smooth muscle cells (VSMCs) in blood vessels after endothelial injury contributes to the onset of atherosclerosis. Heparin is a potent antiproliferative agent for VSMCs in vivo and in vitro. Although heparin has shown promise in suppressing VSMC proliferation after invasive procedures in laboratory animals, the mechanism of its antiproliferative actions is largely unknown.