Inhibition of Rho is required for cAMP-induced melanoma cell differentiation.
Up-regulation of the cAMP pathway by forskolin or alpha-melanocyte stimulating hormone induces melanocyte and melanoma cell differentiation characterized by stimulation of melanin synthesis and dendrite development. Here we show that forskolin-induced dendricity is associated to a disassembly of actin stress fibers. Since Rho controls actin organization, we studied the role of this guanosine triphosphate (GTP)-binding protein in cAMP-induced dendrite formation. Clostridium botulinum C3 exotransferase, which inhibits Rho, mimicked the effect of forskolin in promoting dendricity and stress fiber disruption, while the Escherichia coli toxin cytotoxic necrotizing factor-1 (CNF-1), which activates Rho and the expression of a constitutively active Rho mutant, blocked forskolin-induced dendrite outgrowth. In addition, overexpression of a constitutively active form of the Rho target p160 Rho-kinase (P160(ROCK)) prevented the dendritogenic effects of cAMP. Our results suggest that inhibition of Rho and of its target p160(ROCK) are required events for cAMP-induced dendrite outgrowth in B16 cells. Furthermore, we present evidence that Rho is involved in the regulation of melanogenesis. Indeed, Rho inactivation enhanced the cAMP stimulation of tyrosinase gene transcription and protein expression, while Rho constitutive activation impaired these cAMP-induced effects. This reveals that, in addition to controlling dendricity, Rho also participates in the regulation of melanin synthesis by cAMP.
Buscà
R
R
INSERM U385, Faculté de Médecine, 06107 Nice Cedex 2, France.
Bertolotto
C
C
Abbe
P
P
Englaro
W
W
Ishizaki
T
T
Narumiya
S
S
Boquet
P
P
Ortonne
J P
JP
Ballotti
R
R
D036002:ADP Ribose Transferases / Q000494:pharmacology; D000199:Actins / Q000378:metabolism; D000818:Animals; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000494:pharmacology; D001905:Botulinum Toxins; D002454:Cell Differentiation; D002455:Cell Division; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D003599:Cytoskeleton / Q000502:physiology; D003603:Cytotoxins / Q000494:pharmacology; D003712:Dendrites; D029968:Escherichia coli Proteins; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D008546:Melanoma, Experimental; D051379:Mice; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology; D014407:Tumor Cells, Cultured; D020741:rho GTP-Binding Proteins; D054460:rho-Associated Kinases
D000199:Actins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003603:Cytotoxins; D029968:Escherichia coli Proteins; D047908:Intracellular Signaling Peptides and Proteins; C031815:toxB protein, Clostridium difficile; C060296:cytotoxic necrotizing factor type 1; D005576:Colforsin; D000242:Cyclic AMP; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D020741:rho GTP-Binding Proteins