Hepatocyte growth factor (HGF) stimulates mammalian target of rapamycin (mTOR) in choriocarcinoma cell lines and human trophoblast cells



Introduction:  Hepatocyte growth factor (HGF), interleukin-6 (IL-6) and insulin-like growth factor-II (IGF-II) are involved in the regulation of trophoblast cell migration and invasion. Signal Transducer and Activator of Transcription 3 (STAT3) and Mammalian Target Of Rapamycin (mTOR) signalling regulate cell invasion, growth and proliferation. mTOR plays also a key role during embryogenesis. Knock-out mice embryos die after implantation and blastocysts trophoblast outgrowth is reduced.

Aim:  Stimuli which might trigger such invasive behaviour through mTOR should be defined.

Methods:  The human choriocarcinoma cell lines JEG-3, JAR, the human choriocarcinoma-trophoblast hybrid AC1-M59 and human term trophoblast cells were stimulated with HGF, IL-6 or IGF-II. At several time points, the phosphorylation level of mTOR and STAT3 were tested by Western blot. STAT3 DNA-binding capacity was analyzed by Electrophorectic Mobility Shift Assay (EMSA). To examine the role of mTOR for invasion and proliferation, mTOR expression was silenced by RNA interference (RNAi).

Results:  HGF, IGF-II and IL-6 did neither induce tyrosine (705) phosphorylation of STAT3 nor STAT3 DNA binding capacity as assessed by EMSA. HGF led to an increase of mTOR serine (2448) phosphorylation for all cell types after 15 and 30 min while IL-6 and IGF-II did not induce mTOR phosphorylation. Simultaneously, HGF decreased STAT3 serine (727) phosphorylation. mTOR silencing in AC1-M59 correlates with reduced proliferation and invasion. STAT3 expression was not affected by mTOR knock down.

Conclusion:  HGF triggers mTOR activity in trophoblast and trophoblast-like cells. mTOR is a main regulator of crucial trophoblast functions.