Loss of adhesion in the circulation converts amelanotic metastatic melanoma cells to melanotic by inhibition of AKT.
Direct injection of murine K-1735 melanoma cells into the subcutis, lung, or brain of syngeneic mice produces amelanotic tumors, whereas intravenous injection into the lateral tail vein or internal carotid artery produces both amelanotic and melanotic foci in the lung and the brain respectively. We hypothesized that loss of adhesion in the circulation may contribute to the melanogenic phenotypes of cells. To test this, we used enforced suspension culture of K-1735 cells by consistent rotating culture of K-1735 cells. We found that the expression of the microphthalmia transcription factor (MITF) and melanin-stimulating hormone receptor (MSHR) were upregulated in cells growing in suspension and were accompanied by inhibitions of AKT and ERK, which were reversed in cells upon regrowth as an adherent monolayer. Inhibition of the AKT pathway was responsible for MITF induction by suspension culture. Stable expression of constitutively active AKT significantly repressed the melanogenesis of K-1735 cells injected via circulation. An amelanotic clone of K-1735 cells was resistant to suspension culture-induced MITF, although the inhibition of AKT pathway was intact. Collectively, these data suggest that the inhibition of AKT pathway due to loss of adhesion within the circulation renders a subpopulation of K-1735 cells to produce melanin.
Zhang
Weihua
W
Department of Cancer Biology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Tsan
Rachel
R
Nam
Do-Hyun
DH
Lu
Weixin
W
Fidler
Isaiah J
IJ
D000818:Animals; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007150:Immunohistochemistry; D008545:Melanoma / Q000378:metabolism / Q000473:pathology*; D018328:Melanoma, Amelanotic / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D008809:Mice, Inbred C3H; D051739:Microphthalmia-Associated Transcription Factor / Q000378:metabolism; D009362:Neoplasm Metastasis; D010641:Phenotype; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000096:biosynthesis; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors*; D011979:Receptors, Pituitary Hormone / Q000378:metabolism
D004791:Enzyme Inhibitors; D051739:Microphthalmia-Associated Transcription Factor; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D011979:Receptors, Pituitary Hormone; C029446:MSH receptor; D051057:Proto-Oncogene Proteins c-akt