BRCA1 and p53 protein expression in cultured ovarian surface epithelial cells derived from women with and without a BRCA1 germline mutation.
OBJECTIVE
Mutations in the BRCA1 and TP53 genes are early genetic events leading to (hereditary) ovarian carcinoma. The human ovarian surface epithelium (OSE) is considered the tissue of origin of at least a subset of these tumours. Therefore, OSE cell cultures derived from women harbouring BRCA1 germline mutations can be a potential model to study hereditary ovarian carcinogenesis. In fact, previous in vitro studies indicate phenotypical differences between OSE from women with and without such germline mutations. Therefore, we have assessed whether differences in the expression of BRCA1 and p53 proteins in cultured OSE cells could contribute to these observations.


METHODS
Thirty-two OSE cultures derived from women harbouring a BRCA1 mutation (Predisposed OSE [POSE]) and ten cultures from women without a cancer predisposition (Non predisposed OSE [NPOSE]) were grown under standard conditions. Immunocytochemistry was performed to assess the expression of the BRCA1- and p53 proteins. Ki67 immunocytochemical expression was assessed to determine possible differences in cell cycle status between the two groups. In addition, to study whether wild type p53 was expressed, induction of p53 by cis-platinum was assessed by Western blot.


RESULTS
On the basis of Ki67 expression, three different groups were analyzed. In the group with all cultures that expressed Ki67 no significant difference was observed in BRCA1 (P = 0.19) and p53 expression (P = 0.09). In the group with moderate to high Ki67 expression no difference in BRCA1 expression (P = 0.50) was observed. However, p53 expression was significantly lower in the case group (P = 0.01). The same observation for p53 was made in the group with only high Ki67 expression (P = 0.02). Furthermore, the expression of both BRCA1 and p53 positively correlates with Ki67 expression. In POSE and NPOSE, p53 was induced by cis-platinum to a similar extent.


CONCLUSIONS
Our study indicates differences in the expression of p53, but not in the expression of BRCA1 between POSE and NPOSE. In addition, our findings do suggest the absence of losses of the wild type BRCA1 and p53 genes in the studied OSE cultures. This indicates that losses in these genes cannot account for observed differences in phenotypical traits between POSE and NPOSE, but that differences in levels of p53 might contribute.
Piek
Jurgen M J
JM
Department of Obstetrics and Gynaecology, VU University Medical Center, De Boelelaan 1117, 1081HV, NH, Amsterdam, The Netherlands. jurgen.piek@vumc.nl
Dorsman
Josephine C
JC
Massuger
Leon F
LF
Ansink
Anca C
AC
Weegenaar
Jitske
J
Shvarts
Avi
A
Kenemans
Peter
P
Verheijen
René H M
RH
D000328:Adult; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D005260:Female; D018095:Germ-Line Mutation; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000378:metabolism*; D008875:Middle Aged; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
D019313:BRCA1 Protein; D019394:Ki-67 Antigen; D016159:Tumor Suppressor Protein p53