Submitted on August 24, 2004
Accepted on March 2, 2005
Autocrine production of prostaglandin F2
enhances phenotypic transformation of NRK fibroblasts
Erik G Harks1, Peter H Peters1, Joost L Van Dongen1, Everardus J Van Zoelen1, and Alexander P Theuvenet1*
1 Cell Biology, Radboud University Nijmegen, Nijmegen, The Netherlands
* To whom correspondence should be addressed. E-mail: ATheuv{at}sci.kun.nl.
We have used normal rat kidney (NRK) fibroblasts as an in vitro model system to study cell transformation. These cells obtain a transformed phenotype upon stimulation with growth modulating factors such as retinoic acid (RA) or transforming growth factor 
(TGF). Patch-clamp experiments showed that transformation is paralleled by a profound membrane depolarization from around -70 to -20 mV. This depolarization is caused by a compound in the medium conditioned by transformed NRK cells, which enhances intracellular Ca2+ levels and thereby activates Ca2+-dependent Cl- channels. This compound was identified by ESI mass-spectrometry as prostaglandin F2
(PGF2). The active concentration in the medium conditioned by transformed NRK cells as determined by an enzyme immunoassay was 19.7 ± 2.5 nM (n=6), compared with 1.5 ± 0.1 nM (n=3) by non-transformed NRK cells. Externally added PGF2 could trigger NRK cells that had grown to density arrest to restart their proliferation. This was inhibited when the FP-receptor (i.e. the natural receptor for PGF2) was blocked by Al-8810. RA-induced phenotypic transformation of NRK cells was partially (~25%) suppressed by AL-8810. Our results demonstrate that PGF2 acts as an autocrine enhancer and paracrine inducer of cell transformation, and suggest that it may play a crucial role in carcinogenesis in general.
