Tyrphostin-A47 inhibitable tyrosine phosphorylation of flagellar proteins is associated with distinct alteration of motility pattern in hamster spermatozoa

To acquire fertilizing potential, mammalian spermatozoa must undergo capacitation and acrosome reaction. Our earlier work showed that pentoxifylline (0.45 mM), a sperm motility stimulant, induced an early onset of hamster sperm capacitation associated with tyrosine phosphorylation of 45-80 kDa proteins, localized to the mid-piece of the sperm tail. To assess the role of protein tyrosine phosphorylation in sperm capacitation, we used tyrphostin-A47 (TP-47), a specific protein tyrosine kinase inhibitor. The dose-dependent (0.1-0.5 mM) inhibition of tyrosine phosphorylation by TP-47 was associated with inhibition of hyperactivated motility and 0.5 mM TP-47-treated spermatozoa exhibited a distinct circular motility pattern. This was accompanied by hypo-tyrosine phosphorylation of 45-60 kDa proteins, localized to the principal piece of the intact-sperm and the outer dense fiber-like structures in detergent treated-sperm. Sperm kinematic analysis (by CASA) of spermatozoa, exhibiting circular motility (at 1st hr), showed lower values of straight line velocity, curvilinear velocity and average path velocity, compared to untreated controls. Other TP-47 analogues, tyrphostin-AG1478 and -AG1296, had no effect either on kinematic parameters or sperm protein tyrosine phosphorylation. These studies indicate that TP-47-induced circular motility of spermatozoa is compound-specific and that the tyrosine phosphorylation status of 45-60 kDa flagellum-localized proteins could be key regulators of sperm flagellar bending pattern, associated with the hyperactivation of hamster spermatozoa.     

Apoptotic and non-apoptotic modes of programmed cell death in MCF-7 human breast carcinoma cells

Apoptosis is a specific mode of programmed cell death (PCD), recognized by characteristic morphological and molecular changes. Here we present evidence for a non-apoptotic type of PCD in human MCF-7 breast carcinoma cells. We used TNF-alpha and tyrphostin AG213 to induce apoptotic and non-apoptotic cell death respectively in vitro. Microscopic and immunohistochemical studies, together with DNA analysis and flow cytometric analysis of p53 and bcl-2 oncogene expression, revealed some novel characteristics of non-apoptotic cell death. We show here for the first time some of the biochemical features of an experimentally induced non-apoptotic PCD and emphasize the distinct biochemical events leading to apoptotic and non-apoptotic PCD.     

Effect of synthetic and natural protein tyrosine kinase inhibitors on auxin efflux in zucchini (Cucurbita pepo) hypocotyls

Basipetal auxin transport along the zucchini hypocotyl requires the cell-to-cell translocation of this hormone. Several authors have demonstrated that naphthylphthalamic acid (NPA) blocks auxin efflux. It is believed that NPA binds to a regulatory protein that modulates the activity of the carrier rather than to the carrier itself. A few regulatory mechanisms have been suggested but all lack strong supporting experimental evidence. Four classes of protein tyrosine kinase inhibitors (PTKIs) have been used to investigate the NPA perception pathway. First, six synthetic tyrphostins, inhibitors of the epidermal growth factor receptor (EGF-R), were shown to displace NPA on plasmalemma fractions. The most potent compound was (3,4-dihydroxybenzylidene)-thiocyanoacetamide (tyrphostin A47). The inactive counterpart of tyrphostin A47, (4-methoxybenzylidene)-malononitrile (tyrphostin A1), was unable to displace NPA. Tyrphostins did not inhibit auxin efflux but were antagonists of the inhibition of auxin efflux by NPA. Again, tyrphostin A47 was the most effective and tyrphostin A1 was inactive. Second, the flavonoid genistein, also an EGF-R inhibitor, showed an effect on NPA binding and NPA antagonism similar to the one for the tyrphostins. Daidzein, the inactive counterpart of genistein, was ineffective in displacing NPA and in antagonizing its inhibition of auxin efflux. Two other PTKIs, curcumin and lavendustin A, displayed similar characteristics. Calmodulin antagonists, protein serine/threonine kinase inhibitors, and phosphatase inhibitors were inactive. These results suggest that the NPA binding protein may be related to mammalian tyrosine kinases and may regulate the auxin efflux carrier by phosphorylation.     

Down-modulation of erbB2 activity is necessary but not enough in the differentiation of 3T3-L1 preadipocytes

The high incidence of obesity-related pathologies, led to the study of the mechanisms involved in preadipose cell proliferation and differentiation. Here, we demonstrate that modulation of erbB2, plays a fundamental role during proliferation and adipogenic induction of preadipocytes. Using 3T3-L1 cells as model, we demonstrate that EGF (10 nM, 5 min) in addition to stimulate receptor tyrosine phosphorylation of both erbB2 and EGFR, is able to induce the heterodimer erbB2-EGFR. We treated proliferating 3T3-L1 cells with two inhibitors, AG 825 (IC(50) 0.35 microM, 54 times more selective for erbB2 than for EGFR, IC(50) 19 microM), and AG 879 (IC(50) of 1 microM for erbB2 versus 500 microM for EGFR). We found that both inhibited the proliferation on a dose-dependent basis, reaching a 30% maximal inhibition at 100 microM (P < 0.001) for AG825, and a 20% maximal inhibition at 10 microM (P < 0.001) for AG 879. These results involve erbB2 in 3T3-L1 proliferation. When studying the differentiation process, we found that the action of MIX-Dexa immediately activates MEK, JNK and p38 kinases. We observed that PD98059 and SP600125 (MEK-ERK and JNK inhibitors, respectively) added 1 h prior to the MIX-Dexa induction produced a decrease in erbB2 expression after 6 h, which is even greater than the one produced by the inducers, MIX-Dexa. This work supports erbB2 as a key factor in 3T3-L1 adipogenesis, acting mostly and not only during the proliferative phase but also during the differentiation through modulation of both its expression and activity.     

Tyrphostin AG556 increases the activity of large conductance Ca2+‐activated K+ channels by inhibiting epidermal growth factor receptor tyrosine kinase

The present study was designed to investigate whether large conductance Ca²⁺‐activated K⁺ (BK) channels were regulated by epidermal growth factor (EGF) receptor (EGFR) tyrosine kinase. BK current and channel tyrosine phosphorylation level were measured in BK‐HEK 293 cells expressing both functional α‐subunits and the auxiliary β1‐subunits using electrophysiology, immunoprecipitation and Western blotting approaches, respectively, and the function of rat cerebral basilar arteries was determined with a wire myography system. We found that BK current in BK‐HEK 293 cells was increased by the broad spectrum protein tyrosine kinase (PTK) inhibitor genistein and the selective EGFR tyrosine kinase inhibitor AG556, one of the known tyrphostin. The effect of genistein or AG556 was antagonized by the protein tyrosine phosphatase (PTP) inhibitor orthovanadate. On the other hand, orthovanadate or EGF decreased BK current, and the effect was counteracted by AG556. The tyrosine phosphorylation level of BK channels (α‐ and β1‐subunits) was increased by EGF and orthovanadate, while decreased by genistein and AG556, and the reduced tyrosine phosphorylation of BK channels by genistein or AG556 was reversed by orthovanadate. Interestingly, AG556 induced a remarkable enhancement of BK current in rat cerebral artery smooth muscle cells and relaxation of pre‐contracted rat cerebral basilar arteries with denuded endothelium, and these effects were antagonized by the BK channel blocker paxilline or orthovanadate. These results demonstrate that tyrosine phosphorylation of BK channels by EGFR kinase decreases the channel activity, and inhibition of EGFR kinase by AG556 enhances the channel activity and dilates rat cerebral basilar arteries.     

Trafficking of the human transferrin receptor in plant cells: effects of tyrphostin A23 and brefeldin A

Plant cells possess much of the molecular machinery necessary for receptor-mediated endocytosis (RME), but this process still awaits detailed characterization. In order to identify a reliable and well-characterized marker to investigate RME in plant cells, we have expressed the human transferrin receptor (hTfR) in Arabidopsis protoplasts. We have found that hTfR is mainly found in endosomal (Ara7- and FM4-64-positive) compartments, but also at the plasma membrane, where it mediates binding and internalization of its natural ligand transferrin (Tfn). Cell surface expression of hTfR increases upon treatment with tyrphostin A23, which inhibits the interaction between the YTRF endocytosis signal in the hTfR cytosolic tail and the mu2-subunit of the AP2 complex. Indeed, tyrphostin A23 inhibits Tfn internalization and redistributes most of hTfR to the plasma membrane, suggesting that the endocytosis signal of hTfR is functional in Arabidopsis protoplasts. Co-immunoprecipitation experiments show that hTfR is able to interact with a mu-adaptin subunit from Arabidopsis cytosol, a process that is blocked by tyrphostin A23. In contrast, treatment with brefeldin A, which inhibits recycling from endosomes back to the plasma membrane in plant cells, leads to the accumulation of Tfn and hTfR in larger patches inside the cell, reminiscent of BFA compartments. Therefore, hTfR has the same trafficking properties in Arabidopsis protoplasts as in animal cells, and cycles between the plasma membrane and endosomal compartments. The specific inhibition of Tfn/hTfR internalization and recycling by tyrphostin A23 and BFA, respectively, thus provide valuable molecular tools to characterize RME and the recycling pathway in plant cells.     

BFA‐induced compartments from the Golgi apparatus and trans‐Golgi network/early endosome are distinct in plant cells

Brefeldin A (BFA) is a useful tool for studying protein trafficking and identifying organelles in the plant secretory and endocytic pathways. At low concentrations (5–10 μg ml^?1), BFA caused both the Golgi apparatus and trans‐Golgi network (TGN), an early endosome (EE) equivalent in plant cells, to form visible aggregates in transgenic tobacco BY‐2 cells. Here we show that these BFA‐induced aggregates from the Golgi apparatus and TGN are morphologically and functionally distinct in plant cells. Confocal immunofluorescent and immunogold electron microscope (EM) studies demonstrated that BFA‐induced Golgi‐ and TGN‐derived aggregates are physically distinct from each other. In addition, the internalized endosomal marker FM4‐64 co‐localized with the TGN‐derived aggregates but not with the Golgi aggregates. In the presence of the endocytosis inhibitor tyrphostin A23, which acts in a dose‐ and time‐dependent manner, SCAMP1 (secretory carrier membrane protein 1) and FM4‐64 are mostly excluded from the SYP61‐positive BFA‐induced TGN aggregates, indicating that homotypic fusion of the TGN rather than de novo endocytic trafficking is important for the formation of TGN/EE‐derived BFA‐induced aggregates. As the TGN also serves as an EE, continuously receiving materials from the plasma membrane, our data support the notion that the secretory Golgi organelle is distinct from the endocytic TGN/EE in terms of its response to BFA treatment in plant cells. Thus, the Golgi and TGN are probably functionally distinct organelles in plants.     

白介素-2促进RC-4B/C垂体瘤细胞系增殖

采用细胞培养方法,以＾３Ｈ－ＴｄＲ掺入率反映细胞增殖水平,研究了白介素－２（ＩＬ－２）对大鼠源的ＲＣ－４Ｂ／Ｃ垂体瘤细胞系增殖的影响,并初步分析了ＩＬ－２的作用机制。结果表明：⑴ＩＬ－２（１０－１０００Ｕ／ｍｌ）剂量依赖性地显著提高ＲＣ－４８／Ｃ细胞＾３Ｈ－ＴｄＲ掺入率。⑵特异性酪氨酸蛋白激酶（ＰＴＫ）抑制剂ｔｙｒｐｈｏｓｔｉｎ（１μｍｏｌ／Ｌ）可明显降低ＲＣ－４Ｂ／Ｃ细胞＾３Ｈ－ＴｄＲ掺入率,并     

Tyrphostin AG213对重组人蛋白激酶CK2全酶的抑制动力学

利用基因工程克隆、表达和纯化获得重组人蛋白激酶CK2α和 β亚基 ,在体外等摩尔数混合构成有最大生物活性的重组人CK2全酶 .以重组人CK2全酶为分子靶点 ,研究tyrphostinAG2 13对该全酶的直接作用及其抑制动力学 .通过测定转移到CK2底物上的 [γ 3 2 P]GTP的 [3 2 P]放射活度 ,检测CK2活性 .结果表明 :重组人CK2是一种Ca2 + 、cAMP和cGMP等第二信使非依赖性蛋白激酶 ,与天然CK2的性质一致 .AG2 13对重组人CK2全酶具有很强的抑制作用 ,IC50 为 1 1μmol L ,抑制作用远大于已知CK2的抑制剂 5 ,6 二氯 1 β 呋喃糖苯并咪唑 (DRB)和N (2 氨乙基 ) 5 氯萘 1 硫胺 (A3) .AG2 13对重组人CK2全酶的动力学研究表明 :它与GTP呈现非竞争 竞争性混合型抑制作用 ,抑制常数Ki 和Ki′值分别为 0 6 μmol L与 1 4 μmol L ;与酪蛋白呈非竞争性抑制作用 ,Ki 值为 0 9μmol L .结果说明 ,tyrphostinAG2 13不仅是酪氨酸蛋白激酶的抑制剂 ,而且是一种十分有效的蛋白激酶CK2的抑制剂 .重组人蛋白激酶CK2可作为一种较为简便筛选和开发有效的CK2抑制剂的分子靶点 .     

An Auxin Transport Inhibitor Interferes With Unicellular Gravitropism in Protonemata of the Moss Ceratodon purpureus

Abstract: Gravitropism of the protonemata of the moss Ceratodon purpureus (Hedw.) Brid. was studied after treatment with auxin transport inhibitors and auxin-related substances. The phytotropins NPA (naphthylphthalamic acid) and PBA (pyrenoylbenzoic acid), known to block auxin efflux in higher plants, strongly inhibited gravitropic curvature of the apical protonemal cell. At 3 μM NPA or PBA, approximately 60 % inhibition of curvature was observed; growth rates were less affected. Tyrphostin A47, a known antagonist of NPA effects in higher plants, released the inhibition of moss protonemal gravitropism and restored the full curvature response. Exogenous IAA, even at high concentrations (40 μM), did not interfere with protonemal gravitropism. To account for the results, modified hypotheses for auxin transport and action are discussed.