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Biomedical subjects

S Pillai

Publications and source records attributed to S Pillai.

At least 91 records · Page 5Linked to original sources
PubMed1993

Regulation of keratinocyte growth, differentiation, and vitamin D metabolism by analogs of 1,25-dihydroxyvitamin D.

1,25(OH)2D has numerous actions on many tissues. Analogs of 1,25(OH)2D are being sought that are selective, to further an understanding of the mechanisms of action of 1,25(OH)2D and to improve its therapeutic efficacy. Toward these ends we examined eight analogs of 1,25(OH)2D for their ability to regulate 25OHD metabolism by keratinocytes. Choosing the three most potent, we then examined their ability to inhibit keratinocyte proliferation, stimulate cornified envelope formation (a marker of differentiation), and bind to the 1,25(OH)2D receptor (VDR). 1,25(OH)2-24F2-D, 1,25(OH)2-delta 16-D, and 1,25(OH)2-delta 16,23yne-D proved the most potent in inhibiting 1,25(OH)2D production and stimulating 24,25(OH)2D production, being approximately 10-100 times more potent than 1,25(OH)2D itself. 1,25(OH)2-delta 16-D had the highest affinity for the VDR (fourfold higher than that for 1,25(OH)2D itself) and had the greatest ability both to inhibit proliferation and to stimulate differentiation. 1,25(OH)2-delta 16,23yne-D also had a higher affinity for the VDR but was of less or equal potency in stimulating cornified envelope formation and inhibiting proliferation. 1,25(OH)2-24F2-D, which was the most potent regulator of 25OHD metabolism, had a lower affinity for the VDR and was less potent than 1,25(OH)2D in inhibiting proliferation. Our results indicate that even in the same cell different analogs have different rank orders of potency for the various actions of 1,25(OH)2D.

Calcifediol↗
PubMed1993

Effects of streptozotocin-induced diabetes on neuroendocrine responses to ovariectomy and estrogen replacement in female rats.

The effects of streptozotocin-induced (STZ) diabetes on the negative feedback regulation of LH and FSH were evaluated in adult female rats. Rats were injected with STZ (50 mg/kg) or vehicle and ovariectomized 10 days later. Estrogen (EB; 100 micrograms/kg) or oil injections were given on alternate days, starting on the day of ovariectomy. Blood samples for LH, FSH and PRL assay were taken on days 10, 13, 15 and 17. The rats were decapitated on day 17. One hour prior to sacrifice, one half of the animals were injected with alpha-methyl-p-tyrosine for determination of catecholamine turnover rates. Pituitaries were incubated to determine basal secretion rates. Rats treated with STZ exhibited the expected weight loss and elevation of plasma glucose levels. At the time of ovariectomy, FSH, but not LH or PRL, was depressed in the diabetic rats. The postovariectomy rise in LH and FSH was severely attenuated in the diabetic rats. EB treatment was more effective in lowering LH and FSH levels in the diabetic as compared to the control rats. Median eminence (ME) norepinephrine (NE) and dopamine (DA) turnover was higher in the oil-treated diabetic rats than oil-treated controls. EB also caused a greater decrease in ME NE and DA turnover in the diabetic rats. EB was more effective in decreasing in vitro LH secretion and increasing in vitro PRL secretion from pituitaries of control as compared to STZ-treated animals. These results demonstrated that STZ-induced diabetes leads to an attenuation of LH and FSH release after ovariectomy and potentiates the negative feedback effects of EB.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Binding of collagen causes intracellular mobilization of calcium in human mononuclear cells.

The possibility that extracellular matrix-cell surface interaction might lead to signalling was examined in human mononuclear cells. In mononuclear cells loaded with Indo-1 acetoxymethylester, collagen binding elicited a 2-3 fold increase in cytosolic free calcium concentration within seconds. Plasma fibronectin, serum albumin and heparin did not cause any significant change in intracellular calcium levels. Collagen I, collagen IV and glucosylated collagen I evoked an increase in intracellular Ca++ both in the presence and absence of extracellular calcium. However, in the presence of 2mM EDTA, the increase in cytosolic free calcium concentration caused by collagen I and collagen IV was partly abolished, suggesting the requirement of a cation-dependent interaction of collagen with mononuclear cells. Glucosylated collagen induced intracellular calcium mobilization even in the presence of EDTA suggesting a cation-independent interaction. These results indicate that collagen binding induces rapid mobilization of calcium in human mononuclear cells, apparently from intracellular sources.

Calcium↗
PubMed1992

The major histocompatibility complex class I antigen-binding protein p88 is the product of the calnexin gene.

A 90-kDa phosphoprotein (p90) of the endoplasmic reticulum was identified by a monoclonal antibody generated against human hepatoma cells. Pulse-chase experiments with [32P]phosphate and [35S]methionine demonstrated that p90 formed both stable and transient complexes with other cellular proteins, suggesting its role as a molecular chaperone. This protein associates with heavy chains of major histocompatibility complex class I proteins, suggesting that it is the human homolog of the recently described 88-kDa protein that transiently associates with murine class I molecules in the endoplasmic reticulum. The p90 protein also associates in B lymphocytes with membrane immunoglobulin mu heavy chains and may serve as a chaperone for many membrane-bound polypeptides. A partial human p90 cDNA was cloned from a lambda gt11 expression library and identified as the human homolog of calnexin, a major canine calcium-binding protein found to be associated with the signal-sequence receptor in endoplasmic reticulum membranes.

Amino Acid Sequence↗
PubMed1992

Tetrameric cell-surface MHC class I molecules.

Purified major histocompatibility complex (MHC) class I molecules have been studied at high resolution by X-ray crystallography; the structure is a complex of a single heavy chain, a beta 2-microglobulin light chain and a tightly bound peptide moiety. We show here that complete MHC class I molecules are post-translationally assembled into tetramers (made up of four heavy chains and four beta 2-microglobulin units) and that this tetrameric species is expressed on the cell surface. The multivalent tetrameric structure of class I molecules can be reconciled with models of T-cell activation that invoke antigen-receptor crosslinking, as opposed to models that depend on an allosteric change.

Animals↗
PubMed1992

Lanthanum influx into cultured human keratinocytes: effect on calcium flux and terminal differentiation.

Trivalent cation lanthanum (La) binds to calcium binding sites of cells and either mimics the properties of calcium or inhibits the effects of calcium by displacing calcium from its binding sites. Extracellular calcium induces differentiation of human epidermal keratinocytes in culture, in part by increasing the intracellular calcium levels (Cai). Therefore, in this study we determined the effect of La on differentiation and intracellular calcium levels of keratinocytes. We observed that La inhibited the production of cornified envelopes, a marker for terminal differentiation of keratinocytes. La inhibited the calcium requiring envelope cross-linking enzyme, transglutaminase, in a direct manner, presumably, by displacing calcium from its binding site on the enzyme. La inhibited the influx and the efflux of 45Ca from keratinocytes. Paradoxically, extracellular La appeared to increase the Cai levels of keratinocytes as measured by the fluorescent probe indo-1. However, subsequent experiments revealed that indo-1 bound La with a higher affinity than Ca and emitted fluorescence in the same wavelength as the Ca bound form. Using this probe, we observed that La enters keratinocytes in a dose-dependent fashion and achieves concentrations exceeding 80 nM when the external La concentration is raised to 300 microM. This fully accounted for the apparent increase in Cai when La was added to the cells. Treatment of cells with ionomycin increased indo-1 fluorescence maximally in the presence of La indicating influx of La via this Ca specific ionophore. Our results indicate that La enters cells and inhibits calcium mediated keratinocyte differentiation both by blocking Ca influx and by blocking calcium regulated intracellular processes such as transglutaminase directed cornified envelope formation.

Biological Transport↗
PubMed1992

Adenosine triphosphate stimulates phosphoinositide metabolism, mobilizes intracellular calcium, and inhibits terminal differentiation of human epidermal keratinocytes.

During wound healing, release of ATP from platelets potentially exposes the epidermis to concentrations of ATP known to alter cellular functions mediated via changes in inositol trisphosphate (IP3) and intracellular calcium (Cai) levels. Therefore, we determined whether keratinocytes respond to ATP with a rise in Cai and IP3 and whether such increases are accompanied by a change in their proliferation and differentiation. Changes in Cai were measured in Indo-1-loaded neonatal human foreskin keratinocytes after stimulation with extracellular ATP. Extracellular ATP evoked a transient and acute increase in Cai of keratinocytes both in the presence and in the absence of extracellular calcium. ATP also induced the phosphoinositide turnover of keratinocytes, consistent with its effect in releasing calcium from intracellular sources. ATP did not permeabilize keratinocytes, nor did it promote Ca influx into the cells. The half-maximal effect of ATP was at 10 microM, and saturation was observed at 30-100 microM. UTP, ITP, and ATP gamma S were as effective as ATP in releasing Cai from intracellular stores and competed with ATP for their response, whereas AMP and adenosine were ineffective, suggesting the specificity of P2 purinergic receptors in mediating the ATP response in keratinocytes. Single cell measurements revealed heterogeneity in the calcium response to ATP. This heterogeneity did not appear to be due to differences in the initial Cai response but to subsequent removal of increased Cai by these cells. ATP inhibited terminal differentiation of keratinocytes as measured by [35S]methionine incorporation into cornified envelopes and modestly stimulated incorporation of [3H]thymidine into DNA. Chelation of Cai by bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid reduced basal Cai, blocked the Cai response to ATP, inhibited the basal rate of DNA synthesis, and blocked the ATP-induced increase in DNA synthesis. We conclude that extracellular ATP may be an important physiological regulator of epidermal growth and differentiation acting via IP3 and Cai.

Adenosine Triphosphate↗
PubMed1992

Bilateral progressive essential iris atrophy and keratoconus with coincident features of posterior polymorphous dystrophy: a case report and proposed pathogenesis.

We report the first case known to us of an apparent bilateral association of essential iris atrophy (EIA) and keratoconus (KC), with coincident features of posterior polymorphous dystrophy (PPD). Based on this case and the published natural history and findings of both the irido corneal endothelial (ICE) syndrome and PPD, we propose a new hypothesis for the pathogenesis of the ICE syndrome with associated KC and/or PPD. We suggest that, similar to the genetics of retinoblastoma, the predisposition for either the ICE syndrome or for PPD is inherited as an inactive allele, the so-called "first hit." Inactivation of the second allele, or "second hit," which could occur at any time, might be the product of the background mutation rate or of an environmental trigger. Dedifferentiation or an abnormality in normal development could occur after the first or second hit, resulting in varying clinical patterns. We also concur with other investigators that PPD could be part of the spectrum of the ICE syndrome, owing to similarities in their clinical presentations, histopathology, specular and electron microscopy, and natural history.

Atrophy↗
PubMed1991

Mac-2-binding glycoproteins. Putative ligands for a cytosolic beta-galactoside lectin.

Mac-2, a galactose-binding lectin secretion by activated macrophages, is the major non-integrin laminin-binding protein in these cells. Mac-2 is also expressed by epithelial cells in the intestine and kidney. We wished to identify intestinal glycoproteins other than laminin that have a high affinity for Mac-2 and that could be considered as candidate ligands or partners for this lectin in intestinal epithelium. Certain lines of human colon adenocarcinoma cells produce two Mac-2-binding glycoproteins (M2BP-1 and M2BP-2) that were identified by their avid association with Mac-2 following detergent lysis and immunoprecipitation. These glycoproteins do not share a common epitope with Mac-2, and the interaction between Mac-2 and these proteins is mediated through the carbohydrate-binding domain of Mac-2 and sugar moieties on M2BP-1 and M2BP-2. M2BP-1 (98 kDa) and M2BP-2 (70 kDa) were purified by immunoaffinity chromatography and were specifically eluted with either galactose or lactose. Peptide maps revealed that M2BP-1 and M2BP-2 are structurally related. M2BP-1 is secreted and could conceivably associate with Mac-2 extracellularly. N-terminal sequence analysis of M2BP-2 suggests that these glycoproteins represent a unique subset of candidate ligands for this mammalian beta-galactoside lectin.

Adenocarcinoma↗
PubMed1991

The omega/lambda 5 surrogate immunoglobulin light chain is expressed on the surface of transitional B lymphocytes in murine bone marrow.

The membrane immunoglobulin heavy chain (micron) plays a feedback role during the pre-B stage of B lymphocyte differentiation. In pre-B cell lines, micron associates with two surrogate light chain proteins. The omega chain is disulfide linked to mu and was predicted to be the product of the lambda 5 gene. The iota chain is noncovalently associated with micron. We demonstrate that the omega protein is indeed the product of the lambda 5 gene and that mu, omega, and iota are coassociated in the same complex. Antibodies against the omega/lambda 5 protein demonstrate the existence of a subpopulation of "transitional" bone marrow B cells that express micron and omega on the cell surface. The majority of these cells also express surface kappa light chains, indicating that in B lymphoid ontogeny the lambda 5 gene is inactivated after the onset of kappa light chain expression.

Amino Acid Sequence↗
PubMed1991

Role of intracellular-free calcium in the cornified envelope formation of keratinocytes: differences in the mode of action of extracellular calcium and 1,25 dihydroxyvitamin D3.

Extracellular calcium (Cao) and the steroid hormone 1,25(OH)2D, induce the differentiation of human epidermal cells in culture. Recent studies suggest that increases in intracellular free calcium (Cai) levels may be an initial signal that triggers keratinocyte differentiation. In the present study, we evaluated cornified envelope formation, the terminal event during keratinocyte differentiation, and correlated it with changes in the Cai levels during differentiation of keratinocytes in culture induced by Cao or 1,25(OH)2D. Keratinocytes were grown in different Cao concentrations (0.1 or 1.2 mM) or in the presence of 1,25(OH)2D (10(-11) to 10(-7) M), and the Cai levels were measured using the fluorescent probe Indo-1. Our results suggest that the induction of cornified envelope formation is associated with an increase in Cai level during calcium-induced differentiation. Cao and the calcium ionophore ionomycin acutely increased Cai and cornified envelope formation. In contrast, the effect of 1,25(OH)2D on increasing Cai levels and stimulating cornified envelope formation was long-term, requiring days of treatment with 1,25(OH)2D. Our data are consistent with other recent studies and support the hypothesis that Cao regulates keratinocyte differentiation primarily by acutely increasing their Cai levels. The role of calcium in the mechanism of action of 1,25(OH)2D on keratinocyte differentiation is less clear. The increase in Cai of keratinocytes during 1,25(OH)2D induced differentiation may be essential for or subsequent to its prodifferentiation effects.

Calcitriol↗
PubMed1991

Augmentation by interleukins of the antibody response to a conjugate vaccine against Haemophilus influenzae b.

Interleukins have been recognized as potential adjuvants for use during vaccination. The immunogenicity of some poorly immunogenic bacterial capsular polysaccharides have been improved by conjugation to a protein carrier. Augmentation of the immune response to these glycoconjugates, however, may be realized in the presence of interleukins. The antibody response to one such vaccine which comprises a oligosaccharide derived from the capsule of Haemophilus influenzae type b coupled to CRM197 (HbOC) can be augmented in this manner. A suboptimal dose (0.1 microgram) of HbOC and varying concentrations of IL-1 alpha or IL-1 beta (10(2) - 5 x 10(5) U) were injected intramuscularly at 0 and 2 weeks into Swiss Webster mice. Vaccines were also formulated with and without aluminum phosphate. Antibody to the oligosaccharide was determined by Farr assay. In 3/3 experiments, IL-1 alpha enhanced primary and secondary antibody responses whereas with IL-1 beta, only a slight increase in the primary antibody response was seen but enhanced secondary responses were observed. Thus, IL-1 alpha and to some extent IL-1 beta enhanced the primary and secondary antibody responses to a glycoconjugate vaccine.

Adjuvants, Immunologic↗
PubMed1991

Uncoupling of the calcium-sensing mechanism and differentiation in squamous carcinoma cell lines.

Increases in the intracellular calcium (Cai) levels, induced either by extracellular calcium or by calcium ionophores, stimulate the terminal differentiation of normal human keratinocytes in culture (NHK). Despite extensive differences in phenotypic expression, squamous carcinoma cell lines (SCC lines) display only partial terminal differentiation even in the presence of normal extracellular calcium. Therefore, in this study, we evaluated whether the inability of SCC lines to differentiate normally is due to a defect in achieving adequate levels of Cai. Membrane-bound transglutaminase activity and involucrin levels of the various SCC lines were lower than those of NHK and correlated with their low extent of cornified envelope formation. Ionomycin, a calcium ionophore, acutely increased cornified envelope formation of NHK 60- to 70-fold, but only initiated a 1- to 5-fold increase in SCC lines. Yet resting Cai levels in and the Cai response to various agents of SCC lines were similar or higher than those of NHK. Extracellular calcium evoked a rapid, transient and a slower, sustained increase of Cai. Extracellular ATP increased Cai by a rapid release from intracellular sources. Ionomycin, on the other hand, increased Cai from both intracellular compartments and extracellular sources. Thus, these studies indicate that the abnormalities in differentiation among SCC lines do not appear to involve their calcium-sensing mechanism. An uncoupling of the Cai changes to the synthesis of the precursor molecules required for differentiation may be responsible for the defect in differentiation displayed by these SCC lines.

Adenosine Triphosphate↗