Expression of the ErbB family of receptors in ovarian cancer

OBJECTIVE

To characterize the relative levels of the ErbB family of receptors and their relationship to one another in ovarian cancer.

METHODS

A total of 17 serous cystadenocarcinomas were analyzed for epidermal growth factor receptor (EGF-R or ErbB-1) and ErbB-2, ErbB-3, and ErbB-4 receptor expression by Western blot analysis. Receptor levels were quantified by densitometry and expressed as relative densitometry units normalized to the level of alpha-tubulin. Linear regression analysis was used to analyze receptor group differences. A value of P < or = .05 was considered statistically significant.

RESULTS

All 17 tumors expressed detectable levels of EGF-R, ErbB-2, and ErbB-3, but ErbB-4 expression was not detected. EGF-R levels correlated with ErbB-2 (r = .70, P < .01) and ErbB-3 (r = .52, P < .05) levels. The highest correlation was obtained between the levels of ErbB-2 and ErbB-3 (r = 0.81, P < .001).

CONCLUSION

This study indicates an association between the levels of ErbB receptor family members in ovarian cancer. This association suggests that one or more coordinated regulatory mechanisms may be involved in determining their relative expression levels to one another.

Expression of epidermal growth factor and androgen receptors in ovarian cancer

Ovarian cancer is the second most common malignancy of the female reproductive tract. Approximately 50% of ovarian cancers have elevated levels of epidermal growth factor receptor (EGFR). This overexpression is correlated with a poor prognosis for patient survival. Ovarian cancers also express a number of sex steroid receptors. The androgen receptor (AR) is the predominant sex steroid receptor and is expressed in over 80% of ovarian cancers. We investigated whether a relationship exists between EGFR and AR in ovarian cancer. Sixty serous cystadenocarcinomas were analyzed for their relative levels of EGFR and AR by Western blot analysis. Data were analyzed by Student's t test and linear regression analysis for statistical significance. More than 98% of the tumors expressed detectable levels of EGFR, while 65% of the tumors expressed detectable levels of AR. The levels of EGFR (mean +/- SEM) were found to be significantly (P < 0.01) higher in AR+ (516 +/- 15) than in AR- (304 +/- 57) tumors. EGFR levels significantly correlated to AR levels (r = 0.49, P < 0.001). These results demonstrate an association between EGFR and AR levels in ovarian cancer. Whether this association represents a causal or a casual relationship remains to be determined.

Expression of a truncated epidermal growth factor receptor-like protein (TEGFR) in ovarian cancer

The epidermal growth factor receptor (EGFR) system has been implicated in the etiology of numerous cancers, including that of ovarian cancer. Elevated levels of EGFR are associated with poor patient prognosis. Moreover, a significant number of ovarian cancers express both the receptor and one of its ligands, suggesting an autocrine mechanism for autonomous tumor growth. Because of the implicated role of the EGFR system in neoplasia, a greater understanding of the factors involved in this system is necessary. We have recently characterized a truncated EGFR-like protein (TEGFR) in human placenta, and we now extend this investigation to ovarian cancer. We report that TEGFR is expressed in ovarian cancer and its level correlates to that of EGFR. Moreover, the level of TEGFR is reduced in metastatic compared to primary tumors. These results suggest that TEGFR may play a role in the EGFR system.

Possible role of variant RNA transcripts in the regulation of epidermal growth factor receptor expression in human placenta

Epidermal growth factor receptor (EGFR) plays an important role in growth and differentiation. The human placenta expresses high levels of the receptor. In the placenta, as in many other human tissues, EGFR is encoded by two RNA transcripts of 5.8 kb and 10.5 kb. The placenta also expresses a putative truncated EGFR transcript of 1.8 kb, which encodes only the ligand binding domain of the receptor. The etiology and role of these variant EGFR transcripts is unknown. Using the human placenta as a model to study this area, we report 1) the relationships among these transcripts suggest that the induction of alternate pathways of EGFR RNA processing is involved in their etiologies; 2) the 10.5 kb transcript may be the principal transcript involved in determining the level of the protein receptor; and 3) the isolation of a soluble protein with characteristics consistent with a translational product corresponding to the 1.8 kb transcript, which may act in regulating the activity of EGFR. Together these results suggest that alternate processing of EGFR RNA into variant transcripts may represent a novel mechanism involved in the regulation of the receptor protein.