Signal transducer and activator of transcription 3 is involved in cell growth and survival of human rhabdomyosarcoma and osteosarcoma cells.
BACKGROUND
Stat3 has been classified as a proto-oncogene and constitutive Stat3 signaling appears to be involved in oncogenesis of human cancers. However, whether constitutive Stat3 signaling plays a role in the survival and growth of osteosarcomas, rhabdomyosarcomas, and soft-tissue sarcomas is still unclear.


METHODS
To examine whether Stat3 is activated in osteosarcomas, rhabdomyosarcomas and other soft-tissue sarcomas we analyzed sarcoma tissue microarray slides and sarcoma cell lines using immunohistochemistry and Western blot analysis, respectively, with a phospho-specific Stat3 antibody. To examine whether the activated Stat3 pathway is important for sarcoma cell growth and survival, adenovirus-mediated expression of a dominant-negative Stat3 (Y705F) and a small molecule inhibitor (termed STA-21) were used to inhibit constitutive Stat3 signaling in human sarcoma cell lines expressing elevated levels of Stat3 phosphorylation. Cell viability was determined by MTT assays and induction of apoptosis was analyzed by western blotting using antibodies that specifically recognize cleaved caspases-3, 8, and 9.


RESULTS
Stat3 phosphorylation is elevated in 19% (21/113) of osteosarcoma, 27% (17/64) of rhabdomyosarcoma, and 15% (22/151) of other soft-tissue sarcoma tissues as well as in sarcoma cell lines. Expression of the dominant-negative Stat3 and treatment of STA-21 inhibited cell viability and growth and induced apoptosis through caspases 3, 8 and 9 pathways in human sarcoma cell lines expressing elevated levels of phosphorylated Stat3.


CONCLUSIONS
This study demonstrates that Stat3 phosphorylation is elevated in human rhabdomyosarcoma, osteosarcomas and soft-tissue sarcomas. Furthermore, the activated Stat3 pathway is important for cell growth and survival of human sarcoma cells.
Chen
Chun-Liang
CL
Center for Childhood Cancer, Columbus Children's Research Institute and Department of Pediatrics, The Ohio State University, Columbus, OH 43205, USA. ChenC@pediatrics.ohio-state.edu.
Loy
Abbey
A
Cen
Ling
L
Chan
Christina
C
Hsieh
Fu-Chuan
FC
Cheng
Gong
G
Wu
Bryant
B
Qualman
Stephen J
SJ
Kunisada
Keita
K
Yamauchi-Takihara
Keiko
K
Lin
Jiayuh
J
D017209:Apoptosis / Q000502:physiology; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007150:Immunohistochemistry; D012516:Osteosarcoma / Q000378:metabolism*; D010766:Phosphorylation; D000090063:Proto-Oncogene Mas; D012208:Rhabdomyosarcoma / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D046888:Tissue Array Analysis
C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D020169:Caspases