Theophylline and melanocyte-stimulating hormone effects on gamma-glutamyl transpeptidase and DOPA reactions in cultured melanoma cells

Gamma-glutamyl transpeptidase (GGT), an enzyme of the gamma-glutamyl cycle, was demonstrated in 3 of 6 cell lines derived from a single B16 murine melanoma. Its activity in these cells varied a great deal, appeared to be correlated with the developmental cycle of the cells, and was greatest in young, actively melanogenic cells. Generally, the activity seemed parallel to that of tyrosinase, an enzyme specific for melanin synthesis. The levels of both enzymes tended to decline with prolonged in vitro cultivation, but could be readily renewed after one animal passage. The 3 cell lines that were GGT-negative were nonpigmented and DOPA-negative; so was a nonmelanogenic and nonmelanocytic rhesus cell line. Melanocyte-stimulating hormone (MSH) and theophylline both enhanced pigmentation in murine melanoma cells. The mechanisms of their action apparently differed. We found that theophylline increased both DOPA- and GGT- reactive cells, whereas MSH only increased DOPA-reactive cells. All 3 GGT-positive lines were tumorigenic, and 2 GGT-negative line were not tumorigenic. Our observations suggest that GGT plays a role in the melanin biosynthetic pathway and the its activity is greater in melanoma cells that are tumorigenic.

Gamma-glutamyl transpeptidase in the pigment cells of rhesus eyes

We demonstrated that gamma-glutamyl transpeptidase, one of the enzymes of the gamma-glutamyl cycle, is present in the melanocytes of the eyes of rhesus macaques. Enzyme activity was detected in active melaninsynthesizing melanocytes of the iris stoma and in fetal and neonatal retinal pigment epithelium. It was not detected in adults retinal pigment epithelium or choroidal melanocytes, which are ontogenetically more advanced in development and have little melanogenic activity. Our data show that gamma-glutamyl transpeptidase activity correlates well with growth, early differentiation, and active melanogenesis, and support the hypothesis that in addition to tyrosinase, a second enzyme, such as gamma-glutamyl transpeptidase, takes part in the melanin and pheomelanin metabolic pathways.

A reinvestigation of solar lentigines

Solar lentigines were reinvestigated by a number of different methods to gain a better perspective on their structure. In histologic sections and dopa preparations of split skin, large numbers of melanocytes were seen crowded at the base of the clubbed, budding rete ridges. In split-skin preparations, the scanning electron microscope showed complex systems of ridges, columns, and craters on the underside of the lentiginous epidermis. Oval bodies measuring 15 to 30 mu, with dendrites, were numerous at the apices of the complex epidermal ridges; these bodies were presumed to be melanocytes. In transmission electron micrographs of lentigines, the melanosome complexes inside the keratinocytes were much larger than those found in noninvolved skin. The complex and distinctive architecture of these maculae is probably the result of concurrent proliferation of melanocytes and keratinocytes.

Yellow mutant albinism: cytochemical, ultrastructural, and genetic characterization suggesting multiple allelism

This report describes three sisters, including monozygotic (MZ) twins, with clinical, ultrastructural, and histochemical features typical of yellow mutant albinism; This form of albinism is clinically similar to the tyrosinase-positive type, but hair bulbs showed (1) organelles similar to red hair pheomelanosomes and (2) absence of tyrosinase activity. Classical tyrosinase-negative albinism was found in a maternal cousin of the probands. Pedigree analysis of this family suggests multiple alleles occupying a single locus.

Choroidal melanocytes - a model for studying the aging process in nonreplicative differentiated cells

Choroidal melanocytes differentiate and cease to divide early in postnatal life. They have characteristic organelles, the melanosomes, which are formed from tyrosine in a reaction catalyzed by tyrosinase. As animals become old, enzyme activity declines and the melanosomes show changes that are quantitatively and qualitatively correlated to the animal's increasing age.

Aging of melanocytes

Choroidal melanocytes of the eyes of postnatal animals are classified as postmitotic terminally differentiated cells. They have specific granules, the melanosomes, which undergo changes qualitatively and quantitatively correlated to the animal's increasing age. Epidermal melanocytes, which normally divide only on demand or by stimulation, are classified as intermittent mitotic cells. During their development, lentigines and nevi of the skin show progressive ultrastructural and cytochemical changes similar to those in the choroidal cells, and thus may be considered as aging populations of skin melanocytes. These facts have led to the conclusion that choroidal melanocytes may be used advantageously as a model for studying changes in cells from maturation to senescence.

Cell interactions in the initial contact between cultured melanoma cells and syngeneic macrophages

Thioglycolate-induces peritoneal macrophages from melanoma-bearing mice (immune macrophages) or from control mice (control macrophages) were cultured with syngeneic melanoma cells (P51) to determine the surface characteristics of the effector cells during interaction and destruction of the target cells. After a short culture period (3 hours), immune macrophages had extensive connections via filopodia and ruffled membranes to the surfaces of the melanoma cells; control macrophages did not exhibit the same behavior. A dense region in the cytoplasm immediately beneath the macrophage plasmalemma was observed at the point of contact with the target tumor cell. With longer periods of culture (24 hours), effector cells began phagocytosis of the target cells; immune macrophages, however, had more fine filopodial connections and were more cytostatic than were controls. These observations indicate that one of the initial mechanisms of tumor cell destruction was contact-induced lysis, with phagocytosis playing a minor part.

Microspectrofluorometric analysis of surface antigens of murine melanoma and hamster peritoneal cell hybrids: comparisons of species antigenicity, chromosome number, and tumorigenicity

Somatic cell hybrids from viral fusions of murine melanoma (PAZG) X Chinese hamster peritoneal cells (CH) were compared with respect to surface antigenicity, karyotype and tumorigenicity. One line, F57-(9), which arose from the hybridization of two CH cells and one PAZG cell, had slight (6%) CH chromosome loss but 80%PAZG chromosome loss after 10 months in culture. These cells expressed CH antigens strongly and PAZG antigens weakly. In comparison, another hybrid, F57-(7), formed from one CH and one PAZG cell, lost 20% of its chromosomes after 10 months in vitro. These cells had a stronger expression of PAZG antigens and weaker expression of CH antigens than F57-(9). These findings indicate a direct relationship between chromosome number and antigenicity; tumorigenicity, however, does not appear to depend on the chromosome numbers of the parental cells.

Somatic cell hybrids derived from terminally differentiated rhesus cells and established mouse cell lines

The mechanisms of normal cell differentiation in vivo may be related to some features of cellular aging in vitro in that both are considered to be under genetic control. Diploid rhesus choroidal melanocytes and purified peripheral lymphocytes were fused by means of inactivated Sendai virus with three long-term murine cell lines which lacked either hypoxanthine-guanine phosphoribosyl transferase or thymidine kinase. Cell hybrids were selected by their growth in medium containing hypoxanthine, aminopterin, thymidine, and glycine. G-banded chromosomes were analyzed and elements from both the rhesus and the established mouse cell lines were identified in all metaphases. Hybrids derived from choroid X mouse cells contained more than one chromosome set from the mouse, but those between lymphocytes and established cell lines had only one. However, in every combination continuously replicating hybrids were produced; most of them have undergone more than 40 subculture passages. Our results demonstrate not only that DNA synthesis can be re-initiated in postreplicative cells, but also that DNA continues to replicate in a manner consistent with the life span of the long-term cell line parent.

Characteristics of tyrosinase in B16 melanoma

Tyrosine hydroxylase, dopa oxidase, and peroxidase activities were studied in soluble fractions of B16 melanoma tumor homogenates by polyacrylamide gel disc electrophoresis. Stained gels were scanned photometrically and gel slices were assayed radiometrically. In these preparations, the two bands of tyrosine hydroxylating activity were completely separated from the peroxidase activity but coincided with two major bands of dopa oxidase activity. The third dopa oxidase band coincided with the single band of peroxidase activity. The soluble fraction of cultured cell homogenates had no peroxidase activity, but the two tyrosine hydroxylase bands coincided exactly with the two dopa oxidase bands. Therefore, in the soluble fraction of the murine melanoma bifunctional tyrosinase does exist as two electrophoretically separable forms which are independent of peroxidase.

The effect of MSH on thymidine incorporation by keratinocytes in the epidermal melanin unit

Epidermal melanocytes were observed in the black but not in the white skin of black-and-white spotted guinea pigs. In experiments designed to determine whether melanocyte-stimulating hormone (MSH) affects the incorporation of thymidine by kerationcyte nuclei of the epidermal melanin unit, the labeling index was the same in all skin before MSH administration. After MSH injections, the level of (3H)thymidine incorporation in keratinocytes increased significantly in black skin but not in white. We suggest that through the mediation of melanocytes MSH indirectly afffects keratinocytes in the epidermal melanin unit.

In vivo hybridisation of cultured melanoma cells and isogenic normal mouse cells

Somatic cell hybrids were derived by fusing tumourigenic and melanogenic melanoma (PAZG) cells with normal diploid male mouse cells in vivo. Their chromosomal composition was equivalent to the sum of both parental genomes and included a Y chromosome lacking in the melanoma parent. Our study showed that in PAZG X C57BL hybrids (MP), tumourigenicity was suppressed but pigmentation was expressed.

Mouse satellite DMA in noncentromeric heterochromatin of cultured cells

Specific chromosomes in several mouse lines have interstitial C-bands. In situ hybridization studies indicate that these interstitial bands contain typical mouse satellite DNA.

Chromosomal evolution in a rhesus cell line

Chromosomal evolution was examined in a long-term cell culture derived from Macaca mulatta eye tissue. In addition to the ‘marked’ chromosome that characterizes the rhesus karyotype, other chromosomes that may have originated from it by inversions and translocations were identified at each subculture sampled. Our observations do not warrant the conclusion that all the achromatically distinguished chromosomes observed were ‘marked’ rather than ‘marked’ chromosomes; some, however, resembled the ‘marked’ chromosomes found in Aotus and Cercopithecus.

5-Bromodeoxyuridine-tolerant melanoma cells in vitro and in vivo

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