Asunto(s)
Células Híbridas/fisiología , Neoplasias Experimentales/fisiopatología , Pigmentación , Animales , Núcleo Celular/fisiología , Células Cultivadas , Citoplasma/fisiología , Regulación de la Expresión Génica , Cuerpos de Inclusión Viral/ultraestructura , Melanoma/fisiopatología , Ratones , FenotipoRESUMEN
Binding of beta-melanotropin (betal-melanocyte stimulating hormone) to mouse melanoma cells occurs in a region on the cell surface overlying the Golgi complex. This association was demonstrated by labeling cells with fluorescein isothiocyanate hormone and by locating the Golgi complex with a histochemical test for thiamine pyrophosphatase activity. The biologically active fluorescent hormone appears on the surface and later in vesicles in the malanized cells, as judged by fluorescence microscopy. It is conceivable that internalization of the hormone is instrumental in the process of hormonally induced melanization. Because initial and late events of hormonally induced pigmentation are related to the Golgi complex, it is likely that instructions that follow the attachment of melanotropin to receptors are carried out in a compartmentalized manner.
Asunto(s)
Aparato de Golgi/metabolismo , Hormonas Estimuladoras de los Melanocitos/metabolismo , Melanoma/metabolismo , Receptores de Superficie Celular , Línea Celular , Aparato de Golgi/enzimología , Histocitoquímica , Microscopía Electrónica , Microscopía Fluorescente , Modelos Biológicos , Tiamina Pirofosfatasa/metabolismoRESUMEN
MELANOMA CELLS EXPRESS A PHENOTYPE THAT IS EASY TO RECOGNIZE: the synthesis of melanin. We used this marker to isolate clones of amelanotic variants from large populations of wild-type melanotic clones. Cloudman mouse melanoma (S91, clone M-3, CCL 53.1) was chosen as the parental line because the cells are highly pigmented, grow well as clones in soft agar, and fuse readily with Sendai virus. Subclones (10(7)) of this line were screened without prior mutagenesis, and nine amelanotic variants were isolated. The mutagen ethylmethanesulfonate increased the frequency of variants by three to four orders of magnitude. Wild-type cells had both basal and melanocyte stimulating hormone-inducible tyrosinase activities. The four amelanotic variants that we have examined to date all behaved similarly: they lost basal tyrosinase (EC 1.14.18.1; monophenol monooxygenase) activity but retained melanocyte stimulating hormone-inducible activity; they contained Stage-II melanosomes but no melanized melanosomes; they exhibited growth characteristics similar to those of wild-type cells in culture but produced fewer tumors in mice.