Expression of tSTAT3, pSTAT3727 , and pSTAT3 705 in the epithelial cells of hormone-naïve prostate cancer

Abstract

Background: The signal transducer and activator of transcription 3 (STAT3) pathway is observed to be constitutively activated in several malignancies including prostate cancer (PCa). In the present study, we investigated the expression of total STAT3 (tSTAT3) and two forms of activated phosphorylated STAT3 (pSTAT3⁷²⁷ and pSTAT3⁷⁰⁵ ) in tissue microarrays (TMA) of two cohorts of localized hormone-naïve PCa patients and analyzed associations between the expression and disease outcome.

Methods: The expression of tSTAT3, pSTAT3⁷²⁷ , and pSTAT3⁷⁰⁵ was scored in the nuclei and cytoplasm of prostatic gland epithelial cells in two TMAs of paraffin-embedded prostatic tissue. The TMAs consisted of tissue originated from hormone-naïve radical prostatectomy patients from two different sites: Malmö, Sweden (n = 300) and Dublin, Ireland (n = 99).

Results: The nuclear expression levels of tSTAT3, pSTAT3⁷²⁷ , and pSTAT3⁷⁰⁵ in the epithelial cells of benign glands were significantly higher than in the cancerous glands. Cytoplasmic tSTAT3 levels were also higher in benign glands. Patients with low pSTAT3⁷²⁷ and pSTAT3⁷⁰⁵ levels in the cancerous glands showed reduced times to biochemical recurrence, compared with those with higher levels. No significant trends in nuclear nor in cytoplasmic tSTAT3 were observed in relation to biochemical recurrence in the Malmö cohort. Higher cytoplasmic tSTAT3 was associated with reduced time to biochemical recurrence in the Dublin cohort. Adding the tSTAT3 and pSTAT3 expression data to Gleason score or pathological T stage did not improve their prognostic values.

Conclusions: Low pSTAT3⁷²⁷ and pSTAT3⁷⁰⁵ expression in epithelial cells of cancerous prostatic glands in hormone-naïve PCa was associated with faster disease progression. However, pSTAT3 and tSTAT3 expression did not improve the prognostic value of Gleason score or pathological T stage and may not be a good biomarker in the early hormone naïve stages of PCa.

Keywords: biomarker; immunohistochemistry; prostate cancer; signal transducer and activator of transcription 3; tissue microarray.

Figure 1

Examples of tSTAT3, pSTAT3⁷²⁷, pSTAT3⁷⁰⁵, and p63/AMACR immunostainings in consecutive sections of benign cores and cores with Gleason pattern 3 (GS3) and 5 (GS5). Scale bar = 100 µm. AMACR, α‐methyl acyl‐CoA racemase; pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3 [Color figure can be viewed at wileyonlinelibrary.com]

Figure 2

Nuclear expression of tSTAT3 (A,B), pSTAT3⁷²⁷ (C,D), and pSTAT3⁷⁰⁵ (E,F) in the benign and malignant prostatic epithelium, in the Malmö cohort. A,C, and E, average H score for all benign cores vs all cancer cores. Paired analysis (the Wilcoxon signed‐rank test) showed decreased H score for all markers in the cancer cores. Numbers of patients are shown underneath the graphs. B,D, and F, stratification of individual cores by ISUP 2014 Gleason grade classification. A progressive decrease in mean H score in higher Gleason grades can be observed for all markers (unpaired cores, one‐way ANOVA on Ranks). Number of cores shown below graph. One or two cores were available in each category from each patient. Data are represented as mean ± SEM. All significances indicated are between benign and other group, unless otherwise stated, *P < 0.05, **P < 0.01,***P < 0.001. ANOVA, analysis of variance; pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3 [Color figure can be viewed at wileyonlinelibrary.com]

Figure 3

Cytoplasmic expression of tSTAT3 and pSTAT3⁷²⁷ in the prostatic epithelium, in the Malmö cohort. No cytoplasmic pSTAT3⁷⁰⁵ staining was observed. A,C, Average H score for all benign cores vs all cancer cores. Paired analysis (the Wilcoxon signed‐rank test) showed differences between average tSTAT3 H score in benign and cancer cores. Numbers of patients are shown underneath the graphs. B,D, Stratification of individual cores by ISUP 2014 Gleason grade classification. An elevated expression of pSTAT3 727 was observed in grade 1 (GS < 7) cores (unpaired cores, one‐way ANOVA on ranks). Number of cores shown below graph. One or two cores were available in each category from each patient. Data are represented as mean ± SEM. All significances indicated are between benign and other group, unless otherwise stated, *P < 0.05, **P < 0.01,***P < 0.001. ANOVA, analysis of variance; pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3 [Color figure can be viewed at wileyonlinelibrary.com]

Figure 4

Nuclear expression of tSTAT3 (A,B), pSTAT3⁷²⁷ (C,D), and pSTAT3⁷⁰⁵ (E,F) in the benign and malignant prostatic epithelium, in the Dublin cohort. A,C, and E, Average H score for all benign cores vs all cancer cores. Paired analysis (the Wilcoxon signed‐rank test) showed decreased H score for tSTAT3 in the cancer cores (P < 0.001). Numbers of patients are shown underneath the graphs. B,D, and F, Stratification of individual cores by ISUP 2014 Gleason grade classification. A progressive decrease in mean H score in higher Gleason grades can be observed for all markers (unpaired cores, one‐way ANOVA on ranks). Number of cores shown below graph. One to three cores were available in each category from each patient. Data are represented as mean ± SEM. All significances indicated are between benign and other group, unless otherwise stated, **P < 0.01,***P < 0.001. ANOVA, analysis of variance; pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3 [Color figure can be viewed at wileyonlinelibrary.com]

Figure 5

Cytoplasmic expression of tSTAT3 and pSTAT3⁷²⁷ in the prostatic epithelium, in the Dublin cohort. No cytoplasmic pSTAT3⁷⁰⁵ staining was observed. A,C, Average H score for all benign cores vs all cancer cores. Paired analysis (the Wilcoxon signed‐rank test) showed a significant difference on average tSTAT3 H score between benign and cancer cores (P < 0.05). Numbers of patients are shown underneath the graphs. B,D, Stratification of individual cores by ISUP 2014 Gleason grade classification. No significant differences were observed between the different Gleason grades (unpaired cores, one‐way ANOVA on ranks). Number of cores shown below graph. One to three cores were available in each category from each patient. Data are represented as mean ± SEM. ANOVA, analysis of variance; pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3

Figure 6

Kaplan‐Meier curves of BCR‐free survival in the Malmö cohort for expression of: (A) nuclear tSTAT3, (B) cytoplasmic tSTAT3, (C) nuclear pSTAT3⁷²⁷, (D) cytoplasmic pSTAT3⁷²⁷, and (E) nuclear pSTAT3⁷⁰⁵. All graphs are based on expression in cancer cores. Cutoff between high and low H score was calculated using the Youden index. Log‐rank test statistic was used to determine the P value. BCR, biochemical recurrence; pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3 [Color figure can be viewed at wileyonlinelibrary.com]

Figure 7

Kaplan‐Meier curves of BCR‐free survival in the Dublin cohort for expression of: (A) nuclear tSTAT3, (B) cytoplasmic tSTAT3, (C) nuclear pSTAT3⁷²⁷, (D) cytoplasmic pSTAT3⁷²⁷, and (E) nuclear pSTAT3⁷⁰⁵. All graphs are based on expression in cancer cores. Cutoff between high and low H score was calculated using the Youden index. Log‐rank test statistic was used to determine the P value. pSTAT3, phosphorylated STAT3; STAT3, signal transducer and activator of transcription 3; tSTAT3, total STAT3 [Color figure can be viewed at wileyonlinelibrary.com]