The intracellular mechanism of alpha-fetoprotein promoting the proliferation of NIH 3T3 cells.
OBJECTIVE
The existence and properties of alpha-fetoprotein (AFP) receptor on the surface of NIH 3T3 cells and the effects of AFP on cellular signal transduction pathway were investigated.


METHODS
The effect of AFP on the proliferation of NIH 3T3 cells was measured by incorporation of 3H-TdR. Receptor-binding assay of 125I-AFP was performed to detect the properties of AFP receptor in NIH 3T3 cells. The influences of AFP on the [cAMP]i and the activities of protein kinase A (PKA) were determined. Western blot was used to detect the change of K-ras P21 protein expression.


RESULTS
The proliferation of NIH 3T3 cells treated with 0-80 mg/L of AFP was significantly enhanced. The Scatchard analysis indicated that there were two classes of binding sites with KD of 2.722 x 10(-9)M (Bmax=12810 sites per cell) and 8.931 x 10(-8)M (Bmax=119700 sites per cell) respectively. In the presence of AFP (20 mg/L), the content of cAMP and activities of PKA were significantly elevated . The level of K-ras P21 protein was upregulated by AFP at the concentration of 20 mg/L. The monoclonal antibody against AFP could reverse the effects of AFP on the cAMP content, PKA activity and the expression of K-ras p21 gene.


CONCLUSIONS
The effect of AFP on the cell proliferation was achieved by binding its receptor to trigger the signal transduction pathway of cAMP-PKA and alter the expression of K- ras p21 gene.
Department of Biochemistry and Molecular Biology, Health Science Center, Peking University, Beijing, China.
Meng Sen
MS
Li
Ping Feng
PF
Li
Fei Yi
FY
Yang
Shi Peng
SP
He
Guo Guang
GG
Du
Gang
G
Li
D016475:3T3 Cells; D000818:Animals; D002455:Cell Division; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D051379:Mice; D018000:Receptors, Peptide / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D000509:alpha-Fetoproteins / Q000378:metabolism / Q000502:physiology*
D018000:Receptors, Peptide; D000509:alpha-Fetoproteins; C042144:alpha-fetoprotein receptor, human; C489008:alpha-fetoprotein receptor, mouse; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases