Date of Award
1996
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
The human placenta is comprised of extravillous trophoblast (EVT) cells which invade the uterus and its vasculature establishing maternal-fetal exchange of key molecules. The mechanisms of in vitro EVT cell invasiveness are similar to those of malignant tumor cells but are regulated in situ by locally derived factors. This invasiveness is insufficient for malignancy. The goal of this laboratory is to transform normal EVT cells and induce premalignant, malignant and/or metastatic phenotypes to identify genetic changes relevant to tumor progression.;Two SV40 T antigen (Tag) transformed cell lines (long lived RSVT-2; immortal RSVT2/C) derived from the invasive first trimester EVT cell line, HTR8 were characterized. Both lines exhibited EVT cell markers cytokeratin and cytoplasmic hPL, and were more proliferative and invasive than the parental cells. Increased invasiveness can be explained by (i) reduced expression of tissue inhibitor of metalloprotease (TIMP)-1 mRNA in both lines and (ii) reduced expression of TIMP-2, and plasminogen activator inhibitor (PAI)-1 in RSVT2/C cells. RSVT-2 cells retained sensitivity to the anti-proliferative action of TGF{dollar}\beta{dollar}. RSVT2/C cells were also resistant to its anti-invasive action. Resistance to the anti-invasive action of TGF{dollar}\beta{dollar} may be explained by a lack of TGF{dollar}\beta{dollar}-mediated upregulation of TIMP-1 and PAI-1 mRNA noted with normal HTR8 cells. These results, and the finding that neither cell line was tumorigenic in nude mice, suggest that the SV40 Tag transformants acquired a "premalignant" phenotype, and RSVT2/C cells were possibly more advanced along the tumor progression pathway.;GJIC (dye coupling) and the expression of various connexin proteins and mRNA were also compared in HTR8 and SV40 Tag transformed cells. Only Cx43 was expressed by HTR8 cells. This expression was reduced in RSVT-2, and detectable in RSVT2/C cells. GJIC was also reduced in RSVT-2 cells, and drastically reduced in RSVT2/C cells. TGF{dollar}\beta{dollar} reduced Cx43 mRNA expression and GJIC in HTR8 cells, but not in the SV40 Tag transformants. These findings suggest that a down regulation of connexins and resultant impairment in GJIC are early events in tumor progression.;Gene(s) gained or lost during normal EVT cell transition to premalignancy achieved by SV40 Tag immortalization were also examined. Using differential display, a putatively novel gene was isolated. This gene was identified in RSVT2/C and JAR choriocarcinoma cells but not in the RSVT-2 or HTR8 cells. Sequencing revealed partial homology with Homo sapiens clone 135069 and EST 29905 cDNA. A complete sequence and the function of this gene remain undetermined.
Recommended Citation
Khoo, Nelson K., "Human Placental Trophoblast As A Model For Tumor Progression" (1996). Digitized Theses. 2615.
https://ir.lib.uwo.ca/digitizedtheses/2615