Stage-specific hypermutability of the regA locus of Volvox, a gene regulating the germ-soma dichotomy

Mutation at the regA locus confers on somatic cells of Volvox (which otherwise undergo programmed death) ability to redifferentiate as reproductive cells. Stable mutations at the regA locus, but not at other loci, were induced at high frequency when embryos at one particular stage were exposed to either UV irradiation, novobiocin, nalidixic acid, bleomycin, 4-hydroxyaminoquinoline-1-oxide, 5-bromodeoxyuridine, or 5-fluorouracil. All treatments led to some mutations that were not expressed until the second generation after treatment. The sensitive period was after somatic and reproductive cells of the next generation had been set apart, but before they had undergone cytodifferentiation. Hypermutability occurs in presumptive reproductive cells (in which regA is normally not expressed) somewhat before regA normally acts in somatic cells. We postulate that hypermutability of regA in the reproductive cells at this time reflects a change of state that the locus undergoes as it is inactivated.     

Platelet factor 4 regulates osteoclastic bone resorption in vitro

Platelet factor 4, which inhibits collagenases derived from both human skin and granulocytic extracts, was found to block reversibly parathyroid hormone-stimulated ⁴⁵Ca release from fetal rat bone in vitro. The inhibitory property was equally effective in both actively resorbing bones and in bones stimulated to initiate resorption.     

Arg-Gly-Asp recognition by a cell adhesion receptor requires its 130-kDa alpha subunit

A major Arg-Gly-Asp-directed receptor on M21 human melanoma cells is a heterodimer of alpha and beta chains which under reducing conditions have molecular masses of 130 and 105 kDa, respectively. This receptor is one member of a large family of cell adhesion receptors that shares antigenic determinants with the vitronectin receptor of fibroblasts and the platelet IIb X IIIa complex. Both subunits of the M21 cell adhesion receptor acquire high mannose-type oligosaccharides that are processed before transport to the cell surface. In addition, the alpha chain undergoes a proteolytic cleavage step. Pulse-chase immunoprecipitation analysis demonstrates that, following its synthesis, the beta chain remains unbound to alpha chain for 1-2 h and in this free form is unable to bind an Arg-Gly-Asp containing heptapeptide. Conversely, the biosynthetic precursor of the alpha chain is fully capable of binding the Arg-Gly-Asp-containing peptide immediately after its synthesis. Thus, Arg-Gly-Asp recognition by one member of this cell adhesion receptor family requires its 130-kDa alpha chain which appears to be functional prior to post-translational modifications.     

Conserved residues flanking the thiol/disulfide centers of protein disulfide isomerase are not essential for catalysis of thiol/disulfide exchange.

Protein disulfide isomerase (PDI) catalyzes the oxidative folding of proteins containing disulfide bonds by increasing the rate of disulfide bond rearrangements which normally occur during the folding process. The amino acid sequences of the N- and C-terminal redox active sites (PWCGHCK) in PDI are completely conserved from yeast to man and display considerable identity with the redox-active center of thioredoxin (EWCGPCK). Available data indicate that the two thiol/disulfide centers of PDI can function independently in the isomerase reaction and that the cysteine residues in each active site are essential for catalysis. To evaluate the role of residues flanking the active-site cysteines of PDI in function, a variety of mutations were introduced into the N-terminal active site of PDI within the context of both a functional C-terminal active site and an inactive C-terminal active site in which serine residues replaced C379 and C382. Replacement of non-cysteine residues (W34 to Ser, G36 to Ala, and K39 to Arg) resulted in only a modest reduction in catalytic activity in both the oxidative refolding of RNase A and the reduction of insulin (10-27%), independent of the status of the C-terminal active site. A somewhat larger effect was observed with the H37P mutation where approximately 80% of the activity attributable to the N-terminal domain (approximately 40%) was lost. However, the H37P mutant N-terminal site expressed within the context of an inactive C-terminal domain exhibits 30% activity, approximately 70% of the activity of the N-terminal site alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of pressure on the lateral swimming muscle of the European eel Anguilla anguilla and the deep sea eel Histiobranchus bathybius; results of Challenger cruise 6B/85

1. The viability of Histiobranchus lateral muscle was prolonged up to 7 times by recompression of the tissue. 2. The maximum twitch contraction force of both Anguilla and Histiobranchus was recorded at a pressure between 150 and 350 atm. At 1 atm Anguilla developed 60% maximum force and Histiobranchus 10-20% maximum force. 3. Twitch contraction time doubled for a pressure increase of 400 atm. This effect is predicted to halve the maximum swimming speed at 4000 m and is discussed in relation to muscle force and anaerobic support.     

非甾体抗炎药抑制大鼠血管平滑肌细胞增殖

Abnormal vascular smooth muscle cell (VSMC) proliferation is known to play an important role in the pathogenesis of atherosclerosis, restenosis and instent stenosis. Recent studies suggest that salicylates, in addition to inhibiting cyclooxygenase activity, exert an antiproliferative effect on VSMC growth both in vitro and in vivo. However, whether all non-steroidal anti-inflammatory drugs (NSAID) exert similar antiproliferative effects on VSMCs, and do so via a common mechanism of action, remains unknown. In the present study, we demonstrated that the NSAIDs, aspirin, ibuprofen and sulindac induced a dose-dependent inhibition of proliferation in rat A10 VSMCs (IC50 = 1666 mumol/L, 937 mumol/L and 520 mumol/L, respectively). These drugs did not show significant cytotoxic effects as determined by LDH release assay, even at the highest concentrations tested (aspirin, 5000 mumol/L; ibuprofen, 2500 mumol/L; and sulindac, 1000 mumol/L). Flow cytometric analyses showed that a 48 h exposure of A10 VSMCs to ibuprofen (1000 mumol/L) and sulindac (750 mumol/L) led to a significant G1 arrest (from 68.7 +/- 2.0% of cells in G1 to 76.6 +/- 2.2% and 75.8 +/- 2.2%, respectively, p < 0.05). In contrast, aspirin (2500 mumol/L) failed to induce a significant G1 arrest (68.1 +/- 5.2%). Clearer evidence of a G1 block was obtained by treatment of cells with the mitotic inhibitor, nocodazole (40 ng/ml), for the final 24 h of the experiment. Under these conditions, aspirin still failed to induce a G1 arrest (from 25.9 +/- 10.9% of cells in G1 to 19.6 +/- 2.3%) whereas ibuprofen and sulindac led to a significant accumulation of cells in G1(51.8% +/- 17.2% and 54.1% +/- 10.6%, respectively, p < 0.05). These results indicate that ibuprofen and sulindac inhibit VSMC proliferation by arresting the cell cycle in the G1 phase whereas the effect of aspirin appears to be independent of any special phase of the cell cycle. Irrespective of mechanism, our results suggest that NSAIDs might be of benefit to the treatment of vascular proliferative disorders.     

非甾体抗炎药抑制大鼠血管平滑肌细胞增殖

本文研究了aspirin、ibuprofen和sulindac三种不同结构的非甾体抗炎药(NSAID)对大鼠A10血管平滑肌细胞(VSMC)增殖的影响并探讨其作用机制。方法:细胞计数法观察不同浓度的三种NSAID对细胞增殖的影响,乳酸脱氢酶(LDH)释放分析法测定NSAID的细胞毒作用,流式细胞术分析测定细胞周期。结果:aspirin、ibuprofen和sulindac三种NSAID都对A10 VSMC的增殖有明显抑制作用,且其作用是浓度依赖性的,IC_(50)分别是:aspirin为1666μmol/L,ibuprofen为937μmol/L,sulindac为520μmol/L;其抑制作用不是因细胞毒作用引起;三种NSAID对细胞周期的作用不同,ibuprofen(1000μmol/L)和sulindac(750μmol/L)将细胞阻抑在细胞周期的G_1期(从68.7±2.0%上升到76.6±2.2%和75.8±2.2%,P<0.05),而aspirin(2500μmol/L)对处于细胞周期各期的细胞百分率无明显改变;利用有丝分裂抑制剂nocodazole辅助分析,更清楚地检测到了ibuprofen和sulindac在G_1阻抑,而aspirin仍然不引起处于细胞周期各期的细胞百分率的明显改变。结论:aspirin抗A10 VSMC的增殖作用机制与ibuprofen和sulindac两者的作用机制不同,本研究为三种NSAID成为VSMC增殖性疾病的治疗药物提供了理论依据。