RaLP, a new member of the Src homology and collagen family, regulates cell migration and tumor growth of metastatic melanomas.
The Src homology and collagen (Src) family of adaptor proteins comprises six Shc-like proteins encoded by three loci in mammals (Shc, Rai, and Sli). Shc-like proteins are tyrosine kinase substrates, which regulate diverse signaling pathways and cellular functions, including Ras and proliferation (p52/p46Shc), phosphatidylinositol 3-kinase and survival (p54Rai), and mitochondrial permeability transition and apoptosis (p66Shc). Here, we report the identification, cloning, and sequence characterization of a new member of the Shc family that we termed RaLP. RaLP encodes a 69-kDa protein characterized by the CH2-PTB-CH1-SH2 modularity, typical of the Shc protein family, and expressed, among adult tissues, only in melanomas. Analysis of RaLP expression during the melanoma progression revealed low expression in normal melanocytes and benign nevi, whereas high levels of RaLP protein were found at the transition from radial growth phase to vertical growth phase and metastatic melanomas, when tumor cells acquire migratory competence and invasive potential. Notably, silencing of RaLP expression in metastatic melanomas by RNA interference reduced tumorigenesis in vivo. Analysis of RaLP in melanoma signal transduction pathways revealed that (a) when ectopically expressed in RaLP-negative melanocytes and nonmetastatic melanoma cells, it functions as a substrate of activated insulin-like growth factor-1 and epidermal growth factor receptors and increases Ras/mitogen-activated protein kinase (MAPK) signaling and cell migration, whereas (b) its silencing in RaLP-positive melanoma cells abrogates cell migration in vitro, without affecting MAPK signaling, suggesting that RaLP activates both Ras-dependent and Ras-independent migratory pathways in melanomas. These findings indicate that RaLP is a specific marker of metastatic melanomas, a critical determinant in the acquisition of the migratory phenotype by melanoma cells, and a potential target for novel anti-melanoma therapeutic strategies.
Fagiani
Ernesta
E
Department of Experimental Oncology, European Institute of Oncology, Universita' degli Studi di Milano, Milan, Italy.
Giardina
Giuseppina
G
Luzi
Lucilla
L
Cesaroni
Matteo
M
Quarto
Micaela
M
Capra
Maria
M
Germano
Giovanni
G
Bono
Maria
M
Capillo
Manuela
M
Pelicci
PierGiuseppe
P
Lanfrancone
Luisa
L
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology*; D003001:Cloning, Molecular; D015536:Down-Regulation; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008545:Melanoma / Q000201:enzymology* / Q000235:genetics / Q000473:pathology* / Q000556:secondary; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D055765:Shc Signaling Adaptor Proteins; D014162:Transfection; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
D048868:Adaptor Proteins, Signal Transducing; D012333:RNA, Messenger; C519335:SHC4 protein, human; D055765:Shc Signaling Adaptor Proteins; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D066246:ErbB Receptors; D017526:Receptor, IGF Type 1; D019061:src-Family Kinases; D020928:Mitogen-Activated Protein Kinases