The endoplasmic reticulum stress marker, glucose-regulated protein-78 (GRP78) in visceral adipocytes predicts endometrial cancer progression and patient survival

Abstract

Objective: Currently, accurately identifying endometrial cancer patients at high risk for recurrence remains poor. To ascertain if changes in the endoplasmic reticulum (ER) stress marker, glucose-regulated-protein-78 (GRP78) can serve as a prognosticator in endometrial cancer, we examined GRP78 expression in patient samples to determine its association with clinical outcome.

Methods: A retrospective cohort study was conducted in endometrial cancer patients. Archived specimens of visceral adipocytes and paired endometrial tumors were analyzed by immunohistochemistry for GRP78 and another ER stress marker, C/EBP homologous protein (CHOP). Expression of these markers was correlated with clinico-pathological information and outcomes.

Results: GRP78 expression in visceral adipocytes was detected in 95% of the 179 endometrial cancer patients with analyzable visceral adipocytes. Within individual samples, 24% of adipocytes (range, 0-90%, interquartile range 18%-38%) exhibited GRP78 expression. High visceral adipocyte GRP78 expression positively correlated with advanced-stage disease (p=0.007) and deep myometrial invasion (p=0.004). High visceral adipocyte GRP78 expression was significantly associated with decreased disease-free survival (DFS) in multivariate analyses (hazard ratio 2.88, 95% CI 1.37-6.04, p=0.005). CHOP expression paralleled the GRP78 expression in adipocytes (r=0.55, p<0.001) and in the tumor (p=0.018).

Conclusions: Our study demonstrates that the ER stress markers, GRP78 and CHOP, are elevated in endometrial cancer patients. Furthermore, GRP78 expression levels in visceral adipocytes from these patients were significantly correlated to disease stage and patient survival. Our results demonstrate, for the first time, that the GRP78 levels in endometrial cancer patients may be a prognosticator and aid with clinical risk stratification and focused surveillance.

Fig. 1

GRP78 immunohistochemistry in endometrial tumor and visceral adipocytes. Intensity is determined as negative (0), weak (1+), moderate (2+), and strong (3+) in tumor and adipose tissue. Individual cell: adipocyte from 100× image is magnified. Abbreviation: GRP78, glucose-regulated-protein-78.

Fig. 2

GRP78 expression in visceral adipocytes in endometrial cancer. P-values were based on Fisher's exact test, Chi-square test, Wilcoxon two-sample test, or Kruskal-Wallis test whenever appropriate. (A) Proportion of GRP78 overexpression in normal endometrium is shown for patient with EC and for patient without cancer. (B) Proportion of GRP78 (+) expression in visceral adipocytes by histology. (C) Proportion of tumoral GRP78 overexpression by obesity. Proportion of GRP78 (+) expression in visceral adipocytes based on obesity (D), FIGO stage (E), FIGO grade (F), deep myometrium invasion (G), and LVSI (+) (H). Abbreviations: GRP78, glucose-regulated protein 78; BMI, body mass index (kg/m²); FIGO, the International Federation of Gynecology and Obstetrics; and LVSI, lymphovascular space invasion.

Fig. 3

GRP78 expression and endometrial cancer free survival. Log-rank test. Disease-free survival curves were constructed by visceral adipocyte GRP78 expression using Kaplan-Meier method (A) based on quartiles (B) Survival significance was evaluated for tumoral GRP78 overexpression based on the relative expression to normal endometrium as internal control.

Fig. 4

GRP78 and other ER stress markers in endometrial cancer. (A) Spearman's correlation between percent expression of CHOP and GRP78 in visceral adipocytes. (B) Proportion of GRP78 overexpression in tumor based on CHOP overexpression.