The effect of hemin and of allyl isopropyl acetamide on protein synthesis in rat hepatocytes

Protein synthesis was measured in incubated hepatocytes. While hemin brings about a slight stimulation, allyl isopropyl acetamide (a compound that destroys the heme bound to cytochrome P450) inhibits protein synthesis by a mechanism that appears to result exclusively from depletion of cytoplasmic heme. Indications that in hepatocytes, as in reticulocytes, protein synthesis may be in part regulated by heme at the level of initiation are: i) that inhibition is accompanied by polysome breakdown; ii) that the protein synthesis inhibitor already isolated from rat liver, is hemin reversible iii) that hepatocyte extracts contain a Mr 38,000 phosphoprotein which comigrates with the Mr 38,000 subunit of rabbit initiation factor 2 and iv) that the phosphorylation of both of these subunits is inhibited by hemin.     

PROCUSTE1 encodes a cellulose synthase required for normal cell elongation specifically in roots and dark-grown hypocotyls of Arabidopsis

Mutants at the PROCUSTE1 (PRC1) locus show decreased cell elongation, specifically in roots and dark-grown hypocotyls. Cell elongation defects are correlated with a cellulose deficiency and the presence of gapped walls. Map-based cloning of PRC1 reveals that it encodes a member (CesA6) of the cellulose synthase catalytic subunit family, of which at least nine other members exist in Arabidopsis. Mutations in another family member, RSW1 (CesA1), cause similar cell wall defects in all cell types, including those in hypocotyls and roots, suggesting that cellulose synthesis in these organs requires the coordinated expression of at least two distinct cellulose synthase isoforms.     

Beta-blockers: once or three times a day?

In a double-blind, crossover trial 16 hypertensive patients were treated, in random order, with placebo, metoprolol 300 mg in a single daily dose, or metoprolol 300 mg/day in three doses. Both therapeutic regimens produced detectable plasma metoprolol concentrations and appreciable beta-blockade, estimated from exercise tachycardia, throughout the day. Fluctuations throughout the day in plasma drug concentrations and degree of beta-blockade were insignificant on the thrice-daily regimen, but they varied considerably on the single-dose regimen. Both therapeutic regimens also significantly lowered blood pressure throughout the day. Although the thrice-daily regimen again tended to produce a stronger and less fluctuating hypotensive action, the differences in hypotensive effect between the two regimens were not statistically significant. A single-dose of 300 mg of metoprolol can therefore be recommended if the only aim is to reduce blood pressure but not if a steady degree of beta-blockade is needed.     

Potassium Chloride Pulse Enhances Mitogen-Activated Protein Kinase Activity in Rat Hippocampal Slices

Abstract: Mitogen-activated protein (MAP) kinases have been implicated in multiple responses to extracellular stimuli. In this study we show that MAP kinase activity is enhanced after a KCI pulse. This activation correlates with an increased tyrosine phosphorylation of a 42-kDa protein as determined by antiphosphotyrosine immunoblot. The same band is found in an anti-MAP kinase immunoblot. Activity is enhanced within 1 min, reaches a maximum at 2 min, and returns to basal level after 10 min. A second peak of activity is observed between 12 and 30 min. The activation is completely blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), showing the involvement of the AMPA type of glutamate receptor. Partial inhibition of MAP kinase activation by 2-amino-5-phosphonovalerate (APV) also shows the involvement of the NMDA receptor. Because the KCI pulse used induces long-term potentiation (LTP) in rat hippocampal slice, we conclude that MAP kinase may be involved in neuronal transduction events leading to LTP.     

TGF-beta1-induced cardiac myofibroblasts are nonproliferating functional cells carrying DNA damages

TGF-β₁ induces differentiation and total inhibition of cardiac MyoFb cell division and DNA synthesis. These effects of TGF-β₁ are irreversible. Inhibition of MyoFb proliferation is accompanied with the expression of Smad1, Mad1, p15Ink4B and total inhibition of telomerase activity. Surprisingly, TGF-β₁-activated MyoFbs are growth-arrested not only at G1-phase but also at S-phase of the cell cycle. Staining with TUNEL indicates that these cells carry DNA damages. However, the absolute majority of MyoFbs are non-apoptotic cells as established with two apoptosis-specific methods, flow cytometry and caspase-dependent cleavage of cytokeratin 18. Expression in MyoFbs of proliferative cell nuclear antigen even in the absence of serum confirms that these MyoFbs perform repair of DNA damages. These results suggest that TGF-β₁-activated MyoFbs can be growth-arrested by two checkpoints, the G1/S checkpoint, which prevents cells from entering S-phase and the intra-S checkpoint, which is activated by encountering DNA damage during the S phase or by unrepaired damage that escapes the G1/S checkpoint. Despite carrying of the DNA damages TGF-β₁-activated MyoFbs are highly functional cells producing lysyl oxidase and contracting the collagen matrix.