Tyrosine utilization by cultured melanoma cells: analysis of melanin biosynthesis using [14 C]Tyrosine and [14C]Thiouracil

Alpha v beta 5 integrin-dependent programmed cell death triggered by a peptide mimic of annexin V

The diverse cytoplasmic domain sequences within the various integrin subunits are critical for integrin-mediated signaling into the cell (outside-in signaling) and for activation of ligand binding affinity (inside-out signaling). Here we introduce an approach based on phage display technology to identify molecules that specifically interact with the cytoplasmic domain of the beta 5 integrin subunit. We show that a peptide selected for binding specifically to the beta 5 cytoplasmic domain (VVISYSMPD) induces apoptosis upon internalization. The cell death process induced by VVISYSMPD is sensitive to modulation by growth factors and by protein kinase C (PKC), and it cannot be triggered in beta 5 null cells. Finally, we show that the VVISYSMPD peptide is a mimic of annexin V. Our results suggest a functional link between the alpha v beta 5 integrin, annexin V, and programmed cell death. We propose the term "endothanatos" to designate this phenomenon.

Canine adenovirus type 2 attachment and internalization: coxsackievirus-adenovirus receptor, alternative receptors, and an RGD-independent pathway

The best-characterized receptors for adenoviruses (Ads) are the coxsackievirus-Ad receptor (CAR) and integrins alpha(v)beta(5) and alpha(v)beta(3), which facilitate entry. The alpha(v) integrins recognize an Arg-Gly-Asp (RGD) motif found in some extracellular matrix proteins and in the penton base in most human Ads. Using a canine adenovirus type 2 (CAV-2) vector, we found that CHO cells that express CAR but not wild-type CHO cells are susceptible to CAV-2 transduction. Cells expressing alpha(M)beta(2) integrins or major histocompatibility complex class I (MHC-I) molecules but which do not express CAR were not transduced. Binding assays showed that CAV-2 attaches to a recombinant soluble form of CAR and that Ad type 5 (Ad5) fiber, penton base, and an anti-CAR antibody partially blocked attachment. Using fluorescently labeled CAV-2 particles, we found that in some cells nonpermissive for transduction, inhibition was at the point of internalization and not attachment. The transduction efficiency of CAV-2, which lacks an RGD motif, surprisingly mimicked that of Ad5 when tested in cells selectively expressing alpha(v)beta(5) and alpha(v)beta(3) integrins. Our results demonstrate that CAV-2 transduction is augmented by CAR and possibly by alpha(v)beta(5), though transduction can be CAR and alpha(v)beta(3/5) independent but is alpha(M)beta(2), MHC-I, and RGD independent, demonstrating a transduction mechanism which is distinct from that of Ad2/5.

Regulation of adenovirus membrane penetration by the cytoplasmic tail of integrin beta5

Adenovirus (Ad) cell entry involves sequential interactions with host cell receptors that mediate attachment (CAR), internalization (alphavbeta3 and alphavbeta5), and penetration (alphavbeta5) of the endosomal membrane. These events allow the virus to deliver its genome to the nucleus. While integrins alphavbeta3 and alphavbeta5 both promote Ad internalization into cells, integrin alphavbeta5 selectively facilitates Ad-mediated membrane permeabilization and endosome rupture. In the experiments reported herein, we demonstrate that the intracellular domain of the integrin beta5 subunit specifically regulates Ad-mediated membrane permeabilization and gene delivery. CS-1 melanoma cells expressing a truncated integrin beta5 or a chimeric (beta5-beta3) cytoplasmic tail (CT) supported normal levels of Ad endocytosis but had reduced Ad-mediated gene delivery and membrane permeabilization relative to cells expressing a wild-type integrin beta5. Thin-section electron microscopy revealed that virion particles were capable of being endocytosed into cells expressing a truncated beta5CT, but they failed to escape cytoplasmic vesicles and translocate to the nucleus. Site-specific mutagenesis studies suggest that a C-terminal TVD motif in the beta5CT plays a major role in Ad membrane penetration.

Regulation of cell migration by the integrin beta subunit ectodomain

CS-1 melanoma cells transfected with cDNAs encoding either the beta 3 or beta 5 integrin subunit protein express alpha v beta 3 or alpha v beta 5, respectively, enabling them to adhere to vitronectin yet only alpha v beta 3 promotes cell spreading and migration on this substrate. Following exposure to insulin or insulin-like growth factor, alpha v beta 5-expressing CS-1 cells gain the ability to migrate on vitronectin. To identify structural regions in beta 3 or beta 5 that account for these distinct biological properties, CS-1 cells were transfected with one of two chimeric beta subunit proteins, in which the ecto- and cytoplasmic domains of beta 3 and beta 5 were exchanged (termed alpha v beta 3/5 or alpha v beta 5/3). Surprisingly, alpha v beta 3/5 expressing cells spread and migrate on vitronectin while cells expressing alpha v beta 5/3 do not unless they are exposed to cytokine. These findings suggest that the distinct migratory properties mediated by integrins alpha v beta 3 and alpha v beta 5 and their response to cytokine activation is determined by a sequence(s) within the ectodomain of the integrin beta subunit.

Integrin alpha v beta 5 selectively promotes adenovirus mediated cell membrane permeabilization

Human adenovirus type 2 (Ad2) enters host cells by receptor-mediated endocytosis, an event mediated by the virus penton base binding to cell surface integrins alpha v beta 3 and alpha v beta 5. While both alpha v integrins promote virus internalization, alpha v beta 5 is involved in the subsequent event of membrane permeabilization. Cells transfected with the beta 5 or beta 3 subunit, expressing either alpha v beta 5 and alpha v beta 3, respectively, were capable of supporting Ad2 infection to varying degrees. In this case, cells expressing alpha v beta 5 were significantly more susceptible to Ad2-induced membrane permeabilization, as well as to Ad2 infection, than cells expressing alpha v beta 3. Adenovirus-mediated gene delivery was also more efficient in cells expressing alpha v beta 5. These results suggest that the interaction of alpha v beta 5 with Ad2 penton base facilitates the subsequent step of virus penetration into the cell. These studies provide evidence for the involvement of a cellular receptor in virus-mediated membrane permeabilization and suggest a novel biological role for integrin alpha v beta 5 in the infectious pathway of a human adenovirus.

5-Bromo-2-deoxyuridine regulates invasiveness and expression of integrins and matrix-degrading proteinases in a differentiated hamster melanoma cell

Cell interactions with the extracellular matrix play a critical role in regulating complex processes such as terminal differentiation and tumor progression. In these studies we describe a melanoma cell system that should be useful in addressing the regulation of cell-matrix interactions and the roles they play in regulating differentiation and cell invasiveness. CS (suspension)-1 melanoma cells are relatively well differentiated: they are melanotic, responsive to melanocyte-stimulating hormone, and express TA99, a melanosome membrane differentiation marker. Their repertoire of integrin receptors for extracellular matrix ligands is limited; in particular, they lack receptors for vitronectin, accounting for the observation that they are nonadherent when cultured in the presence of serum. CS-1 cells are noninvasive as well, and express low levels of both metalloproteinases and activated plasminogen activators. Treatment of these cells with melanocyte-stimulating hormone causes them to increase melanin production and assume an arborized phenotype, suggesting that it promotes their further differentiation. In contrast, treatment of CS-1 with the thymidine analog 5-bromodeoxyuridine, converts them to a highly invasive cell population (termed BCS-1) that loses its differentiated properties and responsiveness to melanocyte-stimulating hormone, acquires a broad integrin repertoire (including vitronectin receptors), and expresses elevated levels of metalloproteinases and activated urokinase. From these observations and findings of others on BrdU treatment of other developmental lineages, we hypothesize that BrdU both suppresses differentiation and promotes invasiveness of CS-1 cells. The demonstrated manipulability of CS-1 cells should make them extremely useful for studying the regulation of both terminal differentiation and tumor progression in the melanocyte lineage.

Transport of L-tyrosine by B16/F10 malignant melanocytes: characterization of the process

The main characteristics of L-tyrosine (L-Tyr) uptake by B16/F10 malignant melanocytes are reported. This amino acid can be taken up by two systems, both of them being saturable. The first one would be system L. This system can be studied in cells preloaded with amino acids that are a good substrate for system L, such as L-methionine or L-tryptophan. The kinetic parameters for L-Tyr uptake by this transport system are Vm = 6.5 pmol L-Tyr/10(3) cells.min and Km around 130 microM. The second system, probably the system ASC, shows lower capacity but higher affinity than the former. This system can be detected only in cells previously depleted of amino acids, showing approximate kinetic values of Vm 0.05 pmol L-Tyr/10(3) cells.min and Km around 5 microM. It is shown that the increase in cell density yields a decrease in the rate of L-Tyr uptake by system L, but this increase does not affect the high affinity system, alpha-MSH does not affect significantly the L-Tyr uptake by both systems. 2-Amino bicyclo-(2,2,1)-heptane-2-carboxylic acid produces a remarkable inhibition of the rate of L-Tyr uptake, but alpha-methylaminoisobutyric acid does not affect the rate of transport of this amino acid. The absence of sodium produces a slight but reliable decrease in the rate of L-Tyr uptake, supporting the involvement of two different transport systems. The ionophores monensin and nigericin enhance the transport by system L, but this effect is suppressed by the presence of ouabain. This finding indicates that the (Na+ -K+)-ATPase is essential for the stimulating action of ionophores.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular matrix modulates the function of human melanocytes but not melanoma cells

Normal human epidermal melanocytes are attached to a basement membrane, a specialized form of extracellular matrix (ECM), located between the epithelium and underlying dermal tissues. To determine whether ECM influences pigmented cell behavior in vitro, human epidermal melanocytes and melanoma cells were cultured on uncoated or ECM-coated plastic culture surfaces, and a comparison was made between growth and function in the presence or absence of ECM. Melanocytes cultured on ECM-coated surfaces developed flatter and larger cell bodies and produced more melanin than melanocytes cultured on uncoated surfaces. In the presence of phorbol-myristate-acetate and cholera toxin, the rate of melanocyte replication was increased by ECM. In the absence of these mitogens, ECM significantly enhanced the adhesiveness of nonproliferating melanocytes. ECM had little or no effect on these parameters (morphology, tyrosinase activity, replication) in a pigmented human malignant melanoma cell line. These findings indicate that normal human epidermal pigment cells have the ability to recognize and respond to matrix signals, whereas this capacity appears to be absent in melanoma cells.

Preliminary observations of malignant melanoma therapy using radiolabeled alpha-methyltyrosine

A strategy for cancer therapy using astatine-211-labeled alpha-methyltyrosine (211At-AMT) was studied in cultured B16 melanoma cells and compared to the radiotoxicity of iodine-125-labeled iododeoxyuridine (125IUdR), a thymidine analogue. Both 125I and 211At deliver lethal doses of irradiation to melanoma cells when administered as 125IUdR and 211At-AMT. The alpha decay of astatine-211 is more effective however, needing only a fraction of the cellular radioactivity of 125IUdR to effect comparable clonogenic survival. Compared with 125IUdR, 125I-AMT is not cytotoxic because the range of the low energy electrons released does not interact with DNA. Uptake of radiolabeled AMT by melanotic cells is enhanced by theophylline. This preliminary evidence suggests that 211At-labeled melanin precursors may be exquisitely cytotoxic to B16 melanoma cells.

Effects of actinomycin D and cycloheximide on the increase in tyrosinase activity of hamster amelanotic melanoma cells in vitro

Tyrosinase activity in the Ab hamster amelanotic melanoma cells cultured in serum-free Eagle's MEM increased 3 times after 6 h of primary cell culture. This increase was inhibited completely by cycloheximide, while actinomycin D had no effect on this process. After 24 h of culture in MEM with calf serum, further increase of the tyrosinase activity was inhibited by both cycloheximide and actinomycin D. The data presented may indicate that the increase of tyrosinase activity in the primary cell culture of the Ab melanoma is due initially to the unblocking of translation and later to the activation of transcription of the gene controlling the enzyme.

Aminoacids--precursors of melanin synthesis in hamster melanoma

The role of L-tyrosine, L-phenylalanine, L-dihydroxyphenylalanine (dopa) and L-tryptophan in melanin biosynthesis in melanotic hamster melanoma IC-Sofia was investigated with the aid of 14C-aminoacids. Tyrosine and phenylalanine were found to be the main melanin precursors: about 64.5% of total melanin labeling was due to tyrosine incorporation and 27.4% to phenylalanine incorporation. Negligible proportions of melanin radioactivity (5.7% and 2.4%, respectively) resulted from dopa and tryptophan utilization in melanin synthesis. The involvement of each of the aminoacids under investigation in melanin synthesis in vivo is discussed.

Tyrosine uptake in normal and albino hairbulbs

A method for measuring tyrosine uptake by human hairbulbs was developed to further characterize the process of melanin formation in human tissue. Uptake was determined by incubating fresh anagen hairbulbs in 14C-tyrosine in HEPES-Tris buffer containing cycloheximide and catalase. Uptake for 11 normally pigmented subjects with brown, black, blond and red hair ranged from 295 cpm/24 h per hairbulb for hairbulbs from a blond subject to 6661 cpm/24 h per hairbulb for hairbulbs from a red-haired subject. Hairbulbs from a type IIA (tyrosinase-positive) oculocutaneous albino had an uptake of 2995 cpm/24 h per hairbulb. White hairbulbs had an uptake of 265 cpm/24 h per hairbulb. There was a good correlation (r = 0.86) between the level of uptake and the level of tyrosinase (tyrosine hydroxylase) activity when these values were compared for ten subjects. Uptake was reduced with the inhibition of tyrosinase activity. Uptake was also reduced with low incubation temperatures (4 degrees and 21 degrees C) and with the addition of unlabeled tyrosine to the incubation. From 14% to 19% of the 14C-tyrosine that was taken up could be extracted as 14C-melanin. These results show that the uptake of tyrosine as determined by this experimental method is dependent on the presence of melanocytes and tyrosinase, is quantitatively related to the level of tyrosinase activity, and appears to be a metabolic process. Type IIA albino hairbulb melanocytes appear able to transport adequate amounts of substrate.

Expression of adhesion-related membrane components in adherent versus nonadherent hamster melanoma cells

The existence of integral membrane components that are involved in cell-substratum adhesion has been postulated. Using an immunochemical approach developed in this laboratory, we provide further evidence for the role in cell-substratum adhesion of integral membrane glycoproteins within a molecular weight region of 120,000-140,000. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of material enriched approximately 100-fold in adhesion-related components revealed the 120,000-140,000 Mr glycoproteins in an adherent hamster melanoma cell line. These glycoproteins are greatly reduced in a nonadherent variant. Induction of adhesion in these cells by exposure to BudR is accompanied by re-expression of the surface adhesion antigens.