The BACH1 inhibitor ASP8731 inhibits inflammation and vaso-occlusion and induces fetal hemoglobin in sickle cell disease.

In sickle cell disease (SCD), heme released during intravascular hemolysis promotes oxidative stress, inflammation, and vaso-occlusion. Conversely, free heme can also activate expression of antioxidant and globin genes. Heme binds to the transcription factor BACH1, which represses NRF2-mediated gene transcription. ASP8731, is a selective small molecule inhibitor of BACH1. We investigated the ability of ASP8731 to modulate pathways involved in SCD pathophysiology. In HepG2 liver cells, ASP8731 increased HMOX1 and FTH1 mRNA. In pulmonary endothelial cells, ASP8731 decreased VCAM1 mRNA in response to TNF-α and blocked a decrease in glutathione in response to hemin. Townes-SS mice were gavaged once per day for 4 weeks with ASP8731, hydroxyurea (HU) or vehicle. Both ASP8731 and HU inhibited heme-mediated microvascular stasis and in combination, ASP8731 significantly reduced microvascular stasis compared to HU alone. In Townes-SS mice, ASP8731 and HU markedly increased heme oxygenase-1 and decreased hepatic ICAM-1, NF-kB phospho-p65 protein expression in the liver, and white blood cell counts. In addition, ASP8731 increased gamma-globin expression and HbF+ cells (F-cells) as compared to vehicle-treated mice. In human erythroid differentiated CD34+ cells, ASP8731 increased HGB mRNA and increased the percentage of F-cells 2-fold in manner similar to HU. ASP8731 and HU when given together induced more HbF+ cells compared to either drug alone. In CD34+ cells from one donor that was non-responsive to HU, ASP8731 induced HbF+ cells ~2-fold. ASP8731 and HU also increased HBG and HBA, but not HBB mRNA in erythroid differentiated CD34+ cells derived from SCD patients. These data indicate that BACH1 may offer a new therapeutic target to treat SCD.

The MID1 E3 ligase catalyzes the polyubiquitination of Alpha4 (α4), a regulatory subunit of protein phosphatase 2A (PP2A): novel insights into MID1-mediated regulation of PP2A.

Alpha4 (α4) is a key regulator of protein phosphatase 2A (PP2A) and mTOR in steps essential for cell-cycle progression. α4 forms a complex with PP2A and MID1, a microtubule-associated ubiquitin E3 ligase that facilitates MID1-dependent regulation of PP2A and the dephosphorylation of MID1 by PP2A. Ectopic overexpression of α4 is associated with hepatocellular carcinomas, breast cancer, and invasive adenocarcinomas. Here, we provide data suggesting that α4 is regulated by ubiquitin-dependent degradation mediated by MID1. In cells stably expressing a dominant-negative form of MID1, significantly elevated levels of α4 were observed. Treatment of cells with the specific proteasome inhibitor, lactacystin, resulted in a 3-fold increase in α4 in control cells and a similar level in mutant cells. Using in vitro assays, individual MID1 E3 domains facilitated monoubiquitination of α4, whereas full-length MID1 as well as RING-Bbox1 and RING-Bbox1-Bbox2 constructs catalyzed its polyubiquitination. In a novel non-biased functional screen, we identified a leucine to glutamine substitution at position 146 within Bbox1 that abolished MID1-α4 interaction and the subsequent polyubiquitination of α4, indicating that direct binding to Bbox1 was necessary for the polyubiquitination of α4. The mutant had little impact on the RING E3 ligase functionality of MID1. Mass spectrometry data confirmed Western blot analysis that ubiquitination of α4 occurs only within the last 105 amino acids. These novel findings identify a new role for MID1 and a mechanism of regulation of α4 that is likely to impact the stability and activity level of PP2Ac.

Senataxin, the yeast Sen1p orthologue: characterization of a unique protein in which recessive mutations cause ataxia and dominant mutations cause motor neuron disease.

A severe recessive cerebellar ataxia, Ataxia-Oculomotor Apraxia 2 (AOA2) and a juvenile onset form of dominant amyotrophic lateral sclerosis (ALS4) result from mutations of the Senataxin (SETX) gene. To begin characterization this disease protein, we developed a specific antibody to the DNA/RNA helicase domain of SETX. In murine brain, SETX concentrates in several regions, including cerebellum, hippocampus and olfactory bulb with a general neuronal expression profile, colocalizing with NeuN. In cultured cells, we found that SETX was cytoplasmically diffuse, but in the nucleus, SETX was punctate, colocalizing with fibrillarin, a marker of the nucleolus. In differentiated non-cycling cells, nuclear SETX was not restricted to the nucleolus but was diffuse within the nucleoplasm, suggesting cell-cycle-dependent localization. SETX missense mutations cluster within the N-terminus and helicase domains. Flag tagging at the N-terminus caused protein mislocation to the nucleoplasm and failure to export to the cytoplasm, suggesting that the N-terminus may be essential for correct SETX localization. We report here the first characterization of SETX protein, which may provide future insights into a new mechanism leading to neuron death.

Protein kinase A deficiency causes axially localized neural tube defects in mice.

We have studied the function of protein kinase A (PKA) during embryonic development using a PKA-deficient mouse that retains only one functional catalytic subunit allele, either Calpha or Cbeta, of PKA. The reduced PKA activity results in neural tube defects that are specifically localized posterior to the forelimb buds and lead to spina bifida. The affected neural tube has closed appropriately but exhibits an enlarged lumen and abnormal neuroepithelium. Decreased PKA activity causes dorsal expansion of Sonic hedgehog signal response in the thoracic to sacral regions correlating with the regions of morphological abnormalities. Other regions of the neural tube appear normal. The regional sensitivity to changes in PKA activity indicates that downstream signaling pathways differ along the anterior-posterior axis and suggests a functional role for PKA activation in neural tube development.

Mutation of the Calpha subunit of PKA leads to growth retardation and sperm dysfunction.

The intracellular second messenger cAMP affects cell physiology by directly interacting with effector molecules that include cyclic nucleotide-gated ion channels, cAMP-regulated G protein exchange factors, and cAMP-dependent protein kinases (PKA). Two catalytic subunits, Calpha and Cbeta, are expressed in the mouse and mediate the effects of PKA. We generated a null mutation in the major catalytic subunit of PKA, Calpha, and observed early postnatal lethality in the majority of Calpha knockout mice. Surprisingly, a small percentage of Calpha knockout mice, although runted, survived to adulthood. This growth retardation was not due to decreased GH production but did correlate with a reduction in IGF-I mRNA in the liver and diminished production of the major urinary proteins in kidney. The survival of Calpha knockout mice after birth is dependent on the genetic background as well as environmental factors, but sufficient adult animals were obtained to characterize the mutants. In these animals, compensatory increases in Cbeta levels occurred in brain whereas many tissues, including skeletal muscle, heart, and sperm, contained less than 10% of the normal PKA activity. Analysis of sperm in Calpha knockout males revealed that spermatogenesis progressed normally but that mature sperm had defective forward motility.