Thrombopoietin stimulates migration and activates multiple signaling pathways in hepatoblastoma cells.
Thrombopoietin (TPO), a cytokine that participates in the differentiation and maturation of megakaryocytes, is produced in the liver, but only limited information is available on the biological response of liver-derived cells to TPO. In this study, we investigated whether HepG2 cells express c-Mpl, the receptor for TPO, and whether TPO elicits biological responses and intracellular signaling in this cell type. Specific transcripts for c-Mpl were detected in HepG2 cells by RT-PCR, and expression of the protein was demonstrated by Western blot analysis and immunofluorescence. Exposure of HepG2 cells to TPO was associated with a dose-dependent increase in cell migration and chemoinvasion through Matrigel-coated filters. A checkerboard analysis showed that the effects of TPO on cell migration were dependent on both chemotaxis and chemokinesis. Exposure of HepG2 cells to TPO resulted in the activation of different members of the MAPK family, including ERK and JNK, as assessed using phosphorylation-specific antibodies and immune complex kinase assays. TPO also activated phosphatidylinositol 3-kinase (PI3K) and the downstream kinase Akt in a time-dependent manner. Finally, activation of c-Mpl was associated with increased activation of nuclear factor-kappaB. With the use of specific inhibitors, tyrosine phosphorylation and activation of PI3K were found to be required for the induction of migration in response to TPO. We conclude that TPO exerts biological actions on cultured hepatoblastoma cells via activation of c-Mpl and its downstream signaling.
Romanelli
Roberto G
RG
Dipartimento di Medicina Interna, University of Florence, Viale Morgagni, 85, I-50134 Florence, Italy.
Petrai
Ilaria
I
Robino
Gaia
G
Efsen
Eva
E
Novo
Erica
E
Bonacchi
Andrea
A
Pagliai
Gabriella
G
Grossi
Alberto
A
Parola
Maurizio
M
Navari
Nadia
N
Delogu
Wanda
W
Vizzutti
Francesco
F
Rombouts
Krista
K
Gentilini
Paolo
P
Laffi
Giacomo
G
Marra
Fabio
F
D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D015972:Gene Expression Regulation, Neoplastic; D018197:Hepatoblastoma / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D018121:Receptors, Cytokine / Q000235:genetics / Q000378:metabolism; D053628:Receptors, Thrombopoietin; D015398:Signal Transduction / Q000187:drug effects*; D013926:Thrombopoietin / Q000378:metabolism / Q000494:pharmacology*
D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; C082218:MPL protein, human; D013926:Thrombopoietin; D020929:Mitogen-Activated Protein Kinase Kinases