Interaction of sarcolysine with beta-adrenoreceptors in tumor cells

The sites of specific binding of 3H-L-dihydroalprenolol (3H-DHA) were identified on the surface of ascites sarcoma 37 cells, using competitive displacement and binding of the beta-adrenergic antagonists, 3H-DHA and L-propranolol. These binding sites possessed the properties of beta-adrenergic receptors coupled with adenylate cyclase. Analysis of 3H-DHA binding by the Scatchard method revealed the presence of beta-adrenergic receptors of two types, i. e., with a high (Kd = 0.9-1.0 nM) and low (Kd = 15-20 nM) affinity for 3H-DHA. The number of high affinity receptors was (5.0-7.5) X 10(3); that of low affinity receptors was (20-30) X 10(3) on a per cell basis. Sarcolysine at concentrations of 1-10 microM displaced receptor-bound 3H-DHA, competed with the ligand for the common binding sites and caused, similar to isoproterenol, a short-term elevation of the intracellular cAMP content. Sarcolysine within the same concentration range (2.5-25 microM) caused non-competitive inhibition of the cAMP phosphodiesterase (PDE2) activity of plasma membranes isolated from ascites sarcoma 37 cells. The data obtained point to the functional coupling between beta-adrenergic receptors, adenylate cyclase and membraneous PDE2 of tumour cells as well as to its possible role in the antitumour effect of sarcolysine.     

Interaction of monocytes with tumor cells coated with complement with or without antibody

Raji, a human B lymphoblastoid cell line has the ability to activate the complement cascade by alternate pathway mechanisms with subsequent fixation of C3 to receptors on the Raji cell membrane. Using this property, we examined the role that complement plays in mediating a cytolytic event between human peripheral blood monocytes and Raji cells coated with C3b, antibody, or both. Presence of C3 was confirmed by immune adherence. IgG bound to the Raji membrane was quantitated using I¹²⁵ Staphylococcal protein A assay. The presence of alternate pathway-activated C3 on Raji cells failed to produce monocyte-mediated cytotoxicity. These same target cells subsequently coated with antibody concentration ranging from 200 to >600,000 SPA molecules per Raji cell produced neither enhancement nor inhibition of antibody-dependent, cell-mediated cytotoxicity (ADCC). ADCC was enhanced by complement when complement activation and binding of C3 to the cell surface occurred by classical pathway mechanisms. ADCC of 32% ± 3.2 occurred with undiluted antiserum (625,000 SPA molecules bound/Raji cell) with enhancement to 52% ± 1.1 in the presence of C3. IgG inhibition of ADCC was unaffected by the presence of membrane-bound C3.     

Interaction of liposomes bearing a lipophilic doxorubicin prodrug with tumor cells

When used as nanosized carriers, liposomes enable targeted delivery and decrease systemic toxicity of antitumor agents significantly. However, slow unloading of liposomes inside cells diminishes the treatment efficiency. The problem could be overcome by the adoption of lipophilic prodrugs tailored for incorporation into lipid bilayer of liposomes. We prepared liposomes of egg yolk phosphatidylcholine and yeast phosphatidylinositol bearing a diglyceride conjugate of an antitumor antibiotic doxorubicin (a lipophilic prodrug, DOX-DG) in the membrane to study how these formulations interact with tumor cells. We also prepared liposomes of rigid bilayer-forming lipids, such as a mixture of dipalmitoylphosphatidylcholine and cholesterol, bearing DOX in the inner water volume, both pegylated (with polyethylene glycol (PEG) chains exposed to water phase) and non-pegylated. Efficiency of binding of free and liposomal doxorubicin with tumor cells was evaluated in vitro using spectrofluorimetry of cell extracts and flow cytometry. Intracellular traffic of the formulations was investigated by confocal microscopy; co-localization of DOX fluorescence with organelle trackers was estimated. All liposomal formulations of DOX were shown to distribute to organelles retarding its transport to nucleus. Intracellular distribution of liposomal DOX depended on liposome structure and pegylation. We conclude that the most probable mechanism of the lipophilic prodrug penetration into a cell is liposome-mediated endosomal pathway.     

Interaction with Ppil3 leads to the cytoplasmic localization of Apoptin in tumor cells

Apoptin, a small protein encoded by chicken anemia virus (CAV), induces cell death specifically in cancer cells. In normal cells, Apoptin remains in the cytoplasm; whereas in cancerous cells, it migrates into the nucleus and kills the cell. Cellular localization appears to be crucial. Through a yeast two-hybrid screen, we identified human Peptidyl-prolyl isomerase-like 3 (Ppil3) as one of the Apoptin-associated proteins. Ppil3 could bind Apoptin directly, and held Apoptin in cytoplasm even in tumor cells. We then demonstrated that the nuclearcytoplasmic distribution of Apoptin is related to the expression level of intrinsic Ppil3. Moreover, extrinsic modifying of Ppil3 levels also resulted in nuclearcytoplasmic shuffling of Apoptin. The Apoptin P109A mutant, located between the putative nuclear localization and export signals, could significantly impair the function of Ppil3. Our results suggest a new direction for the localization mechanism study of Apoptin in cells.     

Interaction of tumor and normal blood cells with ethylene oxide and propylene oxide block copolymers

Ethylene oxide and propylene oxide block copolymers (pluronics) are widely known as agents that promote drug penetration across biological barriers. We have studied the interaction of normal and malignant blood cells with pluronics L61 and P85 that have different hydrophobicity. SP2/0 myeloma cells accumulated pluronics while normal cells adsorb most of the polymer on the surface. Interaction of pluronics with cells resulted in drastic changes of membrane microviscosity. Tumor cell membrane microviscosity decreased after pluronics adsorption, in contrast to normal cells, whose membrane microviscosity was enhanced. We suppose that sensitivity of tumor cell membrane microviscosity to the pluronics action correlates with its permeability for molecular substances.     

Interaction of tumor cells and immune system in the metastatic process

The metastatic process is rather complicated and relatively inefficient. Millions of tumor cells are constantly shedding from the primary tumor into the blood stream, but very few of them are able to form metastatic tumors in the different organs or tissues of the host. It is widely accepted that metastatic cells have to possess a complex array of various properties that allow them to complete the metastatic cascade. The realization of the metastatic potential largely depends on the ability of tumor cells to evade host defense mechanisms. The potential role of specific and nonspecific immune mechanisms in the control of metastatic spread and growth is the subject of the present review. A better understanding of the mechanisms of antimetastatic defense is of prime importance for development of efficient immunotherapeutic methods for the treatment and eradication of disseminated tumor metastases.     

Interaction of PD-L1 on tumor cells with PD-1 on tumor-specific T cells as a mechanism of immune evasion: implications for tumor immunotherapy

Programmed death receptor ligand 1 (PD-L1, also called B7-H1) is a recently described B7 family member. In contrast to B7-1 and B7-2, PD-L1 does not interact with either CD28 or CTLA-4. To date, one specific receptor has been identified that can be ligated by PD-L1. This receptor, programmed death receptor 1 (PD-1), has been shown to negatively regulate T-cell receptor (TCR) signaling. Upon ligating its receptor, PD-L1 has been reported to decrease TCR-mediated proliferation and cytokine production. PD-1 gene–deficient mice developed autoimmune diseases, which early led to the hypothesis of PD-L1 regulating peripheral tolerance. In contrast to normal tissues, which show minimal surface expression of PD-L1 protein, PD-L1 expression was found to be abundant on many murine and human cancers and could be further up-regulated upon IFN- stimulation. Thus, PD-L1 might play an important role in tumor immune evasion. This review discusses the currently available data concerning negative T-cell regulation via PD-1, the blockade of PD-L1/PD-1 interactions, and the implications for adoptive T-cell therapies.     

Interaction between daunorubicin and chromatin from Ehrlich ascites tumor cells.

Interaction of daunorubicin with chromatin from Ehrlich ascites tumor cells has been studied by spectrofluorimetry. Daunorubicin interacts with chromatin and displays at least two types of binding. The number of binding sites is reduced when compared to deoxyribonucleic acid. There is no difference in the overall structure of chromatins extracted from cells sensitive or resistant to daunorubicin.     

Interaction of KAI1 on tumor cells with DARC on vascular endothelium leads to metastasis suppression

CD82, also known as KAI1, was recently identified as a prostate cancer metastasis suppressor gene on human chromosome 11p1.2 (ref. 1). The product of CD82 is KAI1, a 40- to 75-kDa tetraspanin cell-surface protein also known as the leukocyte cell-surface marker CD82 (refs. 1,2). Downregulation of KAI1 has been found to be clinically associated with metastatic progression in a variety of cancers, whereas overexpression of CD82 specifically suppresses tumor metastasis in various animal models. To define the mechanism of action of KAI1, we used a yeast two-hybrid screen and identified an endothelial cell-surface protein, DARC (also known as gp-Fy), as an interacting partner of KAI1. Our results indicate that the cancer cells expressing KAI1 attach to vascular endothelial cells through direct interaction between KAI1 and DARC, and that this interaction leads to inhibition of tumor cell proliferation and induction of senescence by modulating the expression of TBX2 and p21. Furthermore, the metastasis-suppression activity of KAI1 was significantly compromised in DARC knockout mice, whereas KAI1 completely abrogated pulmonary metastasis in wild-type and heterozygous littermates. These results provide direct evidence that DARC is essential for the function of CD82 as a suppressor of metastasis.     

Interaction andin vivo growth inhibition of Ehrlich ascites tumor cells by jacalin

Jacalin has been found to agglutinate Ehrlich ascites cells. The agglutination was inhibited by α-glycosides of D-Gal and β -D-Gal(1 → 3)-D-GalNAc suggesting that the lectin-ascites interaction was carbohydrate-specific. There was 21.8% inhibition of tumour (ascites) cell growthin vivo in mice administered 50μg of jacalin by injection for 6 days following intraperitoneal injection of ascites cells. Administration of 100, 150 and 200μg jacalin resulted in 40.2, 57.5 and 83% inhibition respectively. Thein vivo inhibition of tumour cells growth by jacalin was due to its preferential binding with D-Gal-α -(1 → 6) present as terminal residues in the glycoprotein on tumour cell surface.     

Interaction of metallothionein with tumor suppressor p53 protein

Previous reports have shown that metallothionein (MT) may modulate p53 activity through zinc exchange. However, little is known on a direct interaction between MT and p53 in cells. The results demonstrate an interaction between MT and p53 can occur in vitro. The complex between MT and p53 was observed in breast cancer epithelial cells with both wild and inactive type of p53. Furthermore, it was shown that wt-p53 was preferentially associated with Apo-MT. Our data suggest that co-expression of MT and p53 and their complex formation in tumor cells may be involved in regulation of apoptosis in these cells.     

Neuroepithelial cells supply an initial transient wave of MSC differentiation

Mesenchymal stem cells (MSCs) are defined as cells that undergo sustained in vitro growth and are able to give rise to multiple mesenchymal lineages. Although MSCs are already used in regenerative medicine little is known about their in vivo behavior and developmental derivation. Here, we show that the earliest wave of MSC in the embryonic trunk is generated from Sox1+ neuroepithelium but not from mesoderm. Using lineage marking by direct gfp knock-in and Cre-recombinase mediated lineage tracing, we provide evidence that Sox1+ neuroepithelium gives rise to MSCs in part through a neural crest intermediate stage. This pathway can be distinguished from the pathway through which Sox1+ cells give rise to oligodendrocytes by expression of PDGFRbeta and A2B5. MSC recruitment from this pathway, however, is transient and is replaced by MSCs from unknown sources. We conclude that MSC can be defined as a definite in vivo entity recruited from multiple developmental origins.     

Interaction of hexadecyltrimethylammonium bromide with yeast cells

The interaction of hexadecyltrimethylammonium bromide (CTAB) with two yeast cells, Kluyveromyces fragilis and Saccharomyces cerevisiae, has been studied. Strong binding of CTAB to the cell was inferred from 1H and 13C NMR studies, the probable site of binding being the cell-surface. 13C and 31P NMR studies have indicated facilitation of free passage of molecules from outside to inside the cell and vice versa on treatment with CTAB. 31P NMR studies showed that intracellular pH (pHi) was affected in presence of CTAB and the rate of exchange of H+ and PO4(-3) between outside and inside of the cell was 508 s-1. CTAB treatment of yeast cells also affected pH and conductance measurements of the cell-suspension. There was a marked difference in the pH changes around the critical micellar concentration (CMC) of CTAB. The observed pH changes were dependent on (i) CTAB concentration, (ii) pH of the cell-suspension and (iii) pK values of groups from molecules released from the cell. Also, it was shown that ionisation of phosphate diester from polar head groups of membranes constituting cell surface enhanced CTAB binding. Conductance measurements have shown that observed changes were independent of the concentration of yeast cells, but probably dependent on CMC of CTAB.     

Interaction of pseudomonas exoproducts with phagocytic cells

Polymorphonuclear leukocytes play the major role in host defense against infections with Pseudomonas aeruginosa; however, mononuclear cells also may contribute to defense against pulmonary infections with P. aeruginosa. Therefore, we examined the effects of three extracellular products of P. aeruginosa, exotoxin A, alkaline protease, and elastase, on the function of phagocytic cells. Phagocytosis or killing, protein synthesis, and membrane integrity were used as assays of cellular function. Pseudomonas toxin readily inhibited protein synthesis in mouse peritoneal macrophages; in contrast, proteolytic enzymes did not alter protein synthesis, but transiently decreased the sensitivity of macrophages to toxin. High levels of toxin reduced protein synthesis in human peripheral polymorphonuclear leukocytes but did not alter the ability of these cells to kill P. aeruginosa. Elastase and alkaline protease did not cause release of marker enzymes and did not directly inhibit the bactericidal activity of polymorphonuclear leukocytes; killing was reduced due to inactivation of complement components. In conclusion, these potential virulence products do not modify phagocyte function directly and thus do not directly interfere with host response in pseudomonas infections.