Biomedical subjects

A J Valentijn

Publications and source records attributed to A J Valentijn.

8 recordsLinked to original sources

PubMed2004

Anoikis.

Anoikis is apoptosis induced by loss of cell adhesion or inappropriate cell adhesion. Adhesion on the extracellular matrix is important to determine whether a cell is in the correct location and to delete displaced cells by apoptosis. The ability to overcome this requirement has important implications for metastatic cancer. However, how adhesion signals are interpreted by a cell into a life or death decision is complex. In this paper, we will examine this from the point of view of the apoptotic machinery of the cell, and discuss the various ways in which adhesion can influence this process.

Animals↗

PubMed1999

Laminin and beta1 integrins are crucial for normal mammary gland development in the mouse.

We have examined the role of integrin-extracellular matrix interactions in the morphogenesis of ductal structures in vivo using the developing mouse mammary gland as a model. At puberty, ductal growth from terminal end buds results in an arborescent network that eventually fills the gland, whereupon the buds shrink in size and become mitotically inactive. End buds are surrounded by a basement membrane, which we show contains laminin-1 and collagen IV. To address the role of cell-matrix interactions in gland development, pellets containing function-perturbing anti-beta1 integrin, anti-alpha6 integrin, and anti-laminin antibodies respectively were implanted into mammary glands at puberty. Blocking beta1 integrins dramatically reduced both the number of end buds per gland and the extent of the mammary ductal network, compared with controls. These effects were specific to the end buds since the rest of the gland architecture remained intact. Reduced development was still apparent after 6 days, but end buds subsequently reappeared, indicating that the inhibition of beta1 integrins was reversible. Similar results were obtained with anti-laminin antibodies. In contrast, no effect on morphogenesis in vivo was seen with anti-alpha6 integrin antibody, suggesting that alpha6 is not the important partner for beta1 in this system. The studies with beta1 integrin were confirmed in a culture model of ductal morphogenesis, where we show that hepatocyte growth factor (HGF)-induced tubulogenesis is dependent on functional beta1 integrins. Thus integrins and HGF cooperate to regulate ductal morphogenesis. We propose that both laminin and beta1 integrins are required to permit cellular traction through the stromal matrix and are therefore essential for maintaining end bud structure and function in normal pubertal mammary gland development.

Animals↗

PubMed1999

Developmental regulation of Bcl-2 family protein expression in the involuting mammary gland.

Epithelial cells within the mammary gland undergo developmental programmes of proliferation and apoptosis during the pregnancy cycle. After weaning, secretory epithelial cells are removed by apoptosis. To determine whether members of the Bcl-2 gene family could be involved in regulating this process, we have examined whether changes in their expression occur during this developmental apoptotic program in vivo. Bax and Bcl-x were evenly expressed throughout development. However, expression of Bak and Bad was increased during late pregnancy and lactation, and the proteins were present during the time of maximal apoptotic involution. Thereafter, their levels declined. In contrast, Bcl-w was expressed in pregnancy and lactation but was downregulated at the onset of apoptosis. Bcl-2 was not detected in lactating or early involuting mammary gland. Thus, the pro-apoptotic proteins Bax, Bak and Bad, as well as the death-suppressors Bcl-x, Bcl-2 and Bcl-w, are synthesised in mouse mammary gland, and dynamic changes in the expression profiles of these proteins occurs during development. To determine if changes in Bak and Bcl-w expression could regulate mammary apoptosis, their effect on cultured mouse mammary epithelial cells was examined in transient transfection assays. Enforced expression of Bak induced rapid mammary apoptosis, which could be suppressed by coexpression of Bcl-w. In extracts of mammary tissue in vivo, Bak heterodimerized with Bcl-x whereas Bax associated with Bcl-w, but Bak/Bcl-w heterodimers were not detected. Thus, Bak and Bcl-w may regulate cell death through independent pathways. These results support a model in which mammary epithelial cells are primed for apoptosis during the transition from pregnancy to lactation by de novo expression of the death effectors Bak and Bad. It is suggested that these proteins are prevented from triggering apoptosis by anti-apoptotic Bcl-2 family proteins until involution, when the levels of Bcl-w decline. Our study provides evidence that regulated changes in the expression of cell death genes may contribute to the developmental control of mammary apoptosis.

Animals↗

PubMed1995

Effects of losartan on angiotensin and bradykinin peptides and angiotensin-converting enzyme.

Antagonists of the type 1 (AT1) angiotensin II (Ang II) receptor increase renin secretion and plasma Ang II levels, and the increased Ang II levels may counteract the effects of the antagonist. Moreover, other investigators have suggested that the reactive increase in Ang II levels may increase bradykinin (BK) levels through stimulation of the type 2 Ang II receptor (AT2). We investigated the acute effects of the AT1 receptor antagonist losartan (intraarterial injection of 10 mg/kg every 12 h) in male Sprague Dawley rats by measuring circulating angiotensin and BK peptides at 6, 12, and 24 h. Whereas acute losartan administration increased blood angiotensin levels four- to sixfold, blood BK levels were unchanged. We also investigated the effects of losartan administered for 8 days (10 mg/kg every 12 hours, by intraperitoneal injection) on circulating and tissue levels of angiotensin and BK peptides, and angiotensin-converting enzyme (ACE). Losartan increased plasma renin levels 100-fold; plasma angiotensinogen levels decreased to 24% of control; and plasma aldosterone levels were unchanged. Ang II levels in plasma, adrenal, lung, heart, and aorta were increased 25-, 8-, 3.5-, 2.4-, and 14-fold, respectively, by losartan administration. By contrast, kidney Ang II levels decreased to 71% of control, accompanied by a decrease in kidney levels of BK-(1-7) and BK-(1-9). No other tissue showed a change in BK peptide levels, except for a reduction in blood levels of BK-(1-8) to 43% of control. Plasma ACE increased by 13-50%, but tissue ACE levels were unchanged. These data demonstrate that losartan has tissue-specific effects on endogenous levels of angiotensin and BK peptides and indicate that increased BK levels do not contribute to the actions of losartan. The absence of a reactive increase in endogenous kidney levels of Ang II indicates that this tissue is likely to be the most sensitive to AT1 receptor antagonism.

Angiotensin I↗

PubMed1994

Identification of vascular renin-binding proteins by chemical cross-linking: inhibition of binding of renin by renin inhibitors.

OBJECTIVE: To investigate the mechanism of tissue uptake of renin. DESIGN: Angiotensin peptide formation in tissues is dependent on kidney-derived renin, leading us to hypothesize that tissues possess a mechanism for uptake of renin from plasma. METHODS: The binding of [125I]-labelled renin to membranes prepared from various rat tissues was examined. [125I]-labelled renins were cross-linked to membranes with disuccinimidyl suberate and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by autoradiography. RESULTS: Mesenteric artery membranes bound both [125I]-labelled rat renin and [125I]-labelled mouse submandibular gland renin. Cross-linking experiments showed two bands, one of relative molecular mass approximately 105,000 and the other of approximately 75,000. After taking into account the molecular weight of renin, these bands represent renin-binding proteins of relative molecular mass approximately 70,000 and approximately 40,000, respectively. The highest level of these binding proteins was in the mesenteric artery; lower levels were found in the aorta, lung and renal medulla. Renin-binding proteins were also identified in membranes prepared from cultured rat aortic smooth muscle cells. No binding proteins were identified in the kidney cortex, heart, adrenal capsule, adrenal medulla, peri-aortic brown adipose tissue, uterus or pituitary. Binding of renin to mesenteric artery membranes was prevented by inhibitors of renin enzymatic activity (H-77 and SQ 30697); this effect of H-77 showed a dose-dependence parallel to the inhibition of renin activity by this compound, suggesting that the binding of H-77 to the active site of renin prevents its binding to the membranes. CONCLUSIONS: These studies provide evidence for a vascular renin-binding mechanism, which may play a role in the generation of angiotensin peptides in vasculature, and may thus be a determinant of blood pressure. Moreover, one of the actions of inhibitors of renin enzymatic activity in vivo may be to prevent the binding of renin to the vasculature.

Angiotensinogen↗

PubMed1991

Purification and amino-terminal sequence of rat kidney renin: evidence for a two-chain structure.

Rat kidney renin was purified 29,000-fold using a nine-step procedure with a 4% recovery. N-terminal sequence analysis of the non-reduced renin revealed two sequences, indicating a two-chain structure. When compared with the amino acid sequence deduced from the rat preprorenin cDNA sequence, the N-termini of the A and B chains were residues 72 and 355, respectively, of preprorenin. The two-chain structure was confirmed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Rat kidney renin migrated as two broad bands of 35,000-36,000 and 37,000-38,000 Da under non-reducing conditions. Under reducing conditions, the size of both bands decreased by approximately 3000 Da and a band migrated at the buffer front (approximately 5000 Da). The site of cleavage between the two chains of rat renin is analogous to that of mouse submandibular gland renin. However, processing of the prosequence of rat prorenin differs from that of mouse and human prorenin, indicating that the mechanism of activation of prorenin is species-specific.

Amino Acid Sequence↗

PubMed1991

Differential regulation of angiotensin peptide levels in plasma and kidney of the rat.

We compared the effects of the converting enzyme inhibitor perindopril on components of the renin-angiotensin system in plasma and kidney of male Sprague-Dawley rats administered perindopril in their drinking water at two doses (1.4 and 4.2 mg/kg) over 7 days. Eight angiotensin peptides were measured in plasma and kidney: angiotensin-(1-7), angiotensin II, angiotensin-(1-9), angiotensin I, angiotensin-(2-7), angiotensin III, angiotensin-(2-9), and angiotensin-(2-10). In addition, angiotensin converting enzyme activity, renin, and angiotensinogen were measured in plasma, and renin, angiotensinogen, and their respective messenger RNAs were measured in kidney; angiotensinogen messenger RNA was also measured in liver. In plasma, the highest dose of perindopril reduced angiotensin converting enzyme activity to 11% of control, increased renin 200-fold, reduced angiotensinogen to 11% of control, increased angiotensin-(1-7), angiotensin I, angiotensin-(2-7), and angiotensin-(2-10) levels 25-, 9-, 10-, and 13-fold, respectively; angiotensin II levels were not significantly different from control. By contrast, for the kidney, angiotensin-(1-7), angiotensin I, angiotensin-(2-7), and angiotensin-(2-10) levels did not increase; angiotensin II levels fell to 14% of control, and angiotensinogen fell to 12% of control. Kidney renin messenger RNA levels increased 12-fold, but renal renin content and angiotensinogen messenger RNA levels in kidney and liver were not influenced by perindopril treatment. These results demonstrate a differential regulation of angiotensin peptides in plasma and kidney and provide direct support for the proposal that the cardiovascular effects of converting enzyme inhibitors depend on modulation of tissue angiotensin systems. Moreover, the failure of kidney angiotensin I levels to increase with perindopril treatment, taken together with the fall in kidney angiotensinogen levels, suggests that angiotensinogen may be a major rate-limiting determinant of angiotensin peptide levels in the kidney.

Angiotensinogen↗

PubMed1990

Production of rat renin fusion protein in Escherichia coli and the preparation of renin-specific antisera.

Rat renin fused at the N-terminus with Sj26, a 26,000 Da glutathione S-transferase of Schistosoma japonicum, was expressed in Escherichia coli. The fusion protein was soluble and easily purified from crude bacterial lysates by affinity chromatography on immobilised glutathione. The fusion protein possessed no detectable renin activity. Antisera raised in rabbits against the fusion protein were specific for renin. These antisera did not bind soluble renin but bound immobilized renin. By immunoblotting, these antisera demonstrated rat renin to migrate on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as two broad bands of 33,000-34,000 and 35,000-37,000 Da. By immunocytochemistry of rat tissues, these antisera stained renin containing cells in the afferent arteriole of the glomerulus of the kidney, the zona glomerulosa of the adrenal and the corpus luteum of the ovary. However, apart from the afferent arteriole of the kidney, no immunoreactive renin was identified in blood vessels of the kidney, adrenal or ovary. These studies demonstrate that a recombinant renin fusion protein is a valuable alternative approach for the preparation of renin-specific antisera.

Animals↗