Differential gene expression in premalignant human trophoblast: Role of IGFBP-5

Tumorigenesis results from genetic alterations that occur in a stepwise man ner giving rise to cells with increasingly cancer-like characteristics. We used in vitro propagated first trimester human extravillous trophoblast (EV T) cells to identify genetic changes responsible for the transition of the EVT from a normal to premalignant stage. The model used consisted of a norm al invasive EVT (HTR8) cell line and its premalignant derivative (RSVT2/C) generated by transfection with the SV40 Tag and selected using a forced cri sis regimen. RSVT2/C display increased proliferative, migratory and invasiv e behavior, unresponsiveness to anti-proliferative and anti-invasive signal s of TGF beta and a deficiency in gap junctional intercellular communicatio n. These cells, however, were unable to form colonies on soft agar or tumor s in nude mice and are thus defined as premalignant. Differential display r evealed 18 gene sequences, 7 with unknown and 11 with known identity, showi ng altered expression between the normal HTR8 and premalignant RSVT2/C cell lines. The known sequences include the potential tumor suppressors insulin -like growth factor binding protein (IGFBP)-5 and fibronectin (FN) and pote ntial protooncogenes such as chromokinesin (KIF4), alternative splicing fac tor (SF2), dynein, DNA polymerase epsilon (DNApol epsilon) and NF-kappaB ac tivating kinase (NAK). The role of the remaining 4 genes upregulated in the premalignant EVT is presently unknown and these are FK506 binding protein (FKBP) 25, histone protein (HPIHs)-gamma, nucleoporin (Nup) 155 and an 82 k Da acidic human protein. The functional role of IGFBP-5 was examined in the control of proliferation, migration and invasiveness of RSVT2/C cells meas ured in vitro. IGFBP-5 alone had no effect on these properties of RSVT2/C c ells. Furthermore, unlike normal EVT cells, RSVT2/C cells exhibited refract oriness to the migration stimulating signals of IGF-II, which was explained by the loss or downregulation of the IGF type 2 receptor (IGF. R2). RSVT2/ C cells, however, expressed the IGF type 1 receptor (IGF-R1) and responded to IGF-1 by increased proliferation. This response was blocked with increas ing concentrations of IGFBP-5. These results suggest that the loss of IGFBP -5 and possibly IGF-R2, both of which can sequester IGF-1 from IGF-R1, perm its unhindered proliferation of the premalignant EVT in an IGF-1 rich envir onment of the fetal-maternal interface. The functions of the other differen tially expressed genes, some of which are essential for cell cycle progress ion or cell survival require further investigation. (C) 2001 Wiley-Liss, In c.