Effects of insulin-like growth factor (IGF) binding protein-3 (IGFBP-3) on endometrial cancer (HHUA) cell apoptosis and EGF stimulated cell proliferation in vitro.
OBJECTIVE
IGFBP-3 has been demonstrated to stimulate or inhibit cell proliferation independently of its ability to bind IGF and a specific IGFBP-3 receptor has been proposed. EGF has been implicated in the cancer development and carcinogenesis. Only limited data are available on the crosstalk between IGFBP-3 signaling and EGF induced cell survival and signal transduction. The current studies were undertaken to characterize IGFBP-3 binding to endometrial cancer cells (HHUA) and determine its biological effects, as well as whether IGFBP-3 exposure alters the cell proliferation stimulated by EGF.


METHODS
Cell proliferation and apoptosis were analyzed by ELISA using specific antibodies. The interaction between HHUA cell and IGFBP-3 was analyzed using a biosensor. The phosphorylation abundance of specific proteins and their phosphorylation in response to EGF and IGFBP-3 was analyzed by immunoprecipitation followed by immunoblotting.


RESULTS
Biosensor analysis showed that IGFBP-3 could bind to HHUA cell surface. IGFBP-3 inhibited BrdU uptake, potentiated ssDNA production and induced p53 in HHUA cells. Although EGF stimulated HHUA cell proliferation and Akt phosphorylation, IGFBP-3 inhibited cell proliferation and Akt phosphorylation that had been stimulated by EGF. However, EGF receptor phosphorylation and expression were not reduced by IGFBP-3. Since HHUA cells lack IGF receptors and do not show biological response to IGF these results suggest that IGFBP-3 can bind to HHUA cells, inhibit cell proliferation and induce apoptosis independently of its ability to bind to IGFs possibly by binding to an IGFBP-3 receptor.


CONCLUSIONS
Taken together these findings demonstrate that IGFBP-3 binds to HHUA cell surface, and inhibits cell division induced by EGF, possibly by modulating the EGF-mediated signal transduction system.
Mochizuki
Tomoko
T
Department of Obstetrics and Gynecology, School of Medicine, Kyorin University, Mitaka, Tokyo, Japan. sakaik@aol.com
Sakai
Keiji
K
Iwashita
Mitsutoshi
M
D000964:Antimetabolites, Antineoplastic / Q000378:metabolism; D017209:Apoptosis; D015374:Biosensing Techniques; D001973:Bromodeoxyuridine / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D004277:DNA, Single-Stranded / Q000032:analysis / Q000378:metabolism; D016889:Endometrial Neoplasms / Q000737:chemistry / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*
D000964:Antimetabolites, Antineoplastic; D004277:DNA, Single-Stranded; D018972:Insulin-Like Growth Factor Binding Protein 3; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D001973:Bromodeoxyuridine