Intravital imaging reveals transient changes in pigment production and Brn2 expression during metastatic melanoma dissemination.
How melanoma acquire a metastatic phenotype is a key issue. One possible mechanism is that metastasis is driven by microenvironment-induced switching between noninvasive and invasive states. However, whether switching is a reversible or hierarchical process is not known and is difficult to assess by comparison of primary and metastatic tumors. We address this issue in a model of melanoma metastasis using a novel intravital imaging method for melanosomes combined with a reporter construct in which the Brn-2 promoter drives green fluorescent protein (GFP) expression. A subpopulation of cells containing little or no pigment and high levels of Brn2::GFP expression are motile in the primary tumor and enter the vasculature. Significantly, the less differentiated state of motile and intravasated cells is not maintained at secondary sites, implying switching between states as melanoma cells metastasize. We show that melanoma cells can switch in both directions between high- and low-pigment states. However, switching from Brn2::GFP high to low was greatly favored over the reverse direction. Microarray analysis of high- and low-pigment populations revealed that transforming growth factor (TGF)beta2 was up-regulated in the poorly pigmented cells. Furthermore, TGFbeta signaling induced hypopigmentation and increased cell motility. Thus, a subset of less differentiated cells exits the primary tumor but subsequently give rise to metastases that include a range of more differentiated and pigment-producing cells. These data show reversible phenotype switching during melanoma metastasis.
Pinner
Sophie
S
Tumour Cell Biology Laboratory, Institute of Cancer Research, London, United Kingdom.
Jordan
Peter
P
Sharrock
Kirsty
K
Bazley
Laura
L
Collinson
Lucy
L
Marais
Richard
R
Bonvin
Elise
E
Goding
Colin
C
Sahai
Erik
E
D000818:Animals; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002465:Cell Movement; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D020869:Gene Expression Profiling; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D008544:Melanocytes / Q000378:metabolism; D008546:Melanoma, Experimental / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D009361:Neoplasm Invasiveness; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D050809:POU Domain Factors / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012878:Skin Neoplasms / Q000378:metabolism* / Q000556:secondary; D012880:Skin Pigmentation; D053781:Transforming Growth Factor beta2 / Q000235:genetics / Q000378:metabolism
D014408:Biomarkers, Tumor; D009419:Nerve Tissue Proteins; D050809:POU Domain Factors; D053781:Transforming Growth Factor beta2; C485184:enhanced green fluorescent protein; C074066:Pou3f2 protein, mouse; D049452:Green Fluorescent Proteins; D008156:Luciferases