SOCS3 protein expression predicts the responses of advanced non-small cell lung cancer patients to platinum-based chemotherapy

Abstract

Background: This study sought to assess the relationship between suppressor of cytokine signaling 3 (SOCS3) expression, SOCS3 promoter methylation status, and platinum-based chemotherapy responses in advanced non-small cell lung cancer (NSCLC) patients.

Methods: A total of 400 advanced NSCLC patients with inoperable disease were enrolled in this study. All the patients underwent platinum-based chemotherapy treatment, and the clinical and prognostic outcomes of these patients were analyzed. The SOCS3 protein expression and SOCS3 promoter methylation status of the tumor tissues in these patients were also tested by immunohistochemistry and polymerase chain reaction (PCR), respectively. In addition, we knocked down SOCS3 expression via small-interfering RNA (siRNA) in the lung cancer cell lines and conducted in vitro analyses to examine cell viability and apoptosis.

Results: Patients with higher expression levels of SOCS3 were found to have a lower average tumor stage, higher average tumor differentiation, and higher rates of positive chemotherapy responses than those with lower expression levels of SOCS3. SOCS3 promoter methylation was also found to be correlated with chemotherapy responses in these patients. In the prognostic analyses, only SOCS3 expression, but not SOCS3 promoter methylation, was found to be predictive of outcomes in advanced NSCLC patients. We also found that the pro-apoptotic effects of SOCS3 were mediated by the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathways in the lung cancer cells.

Conclusions: Currently, there is a lack of reliable biomarkers for predicting the responses of NSCLC patients to chemotherapy. Our results may aid in clinical evaluations of NSCLC patients.

Keywords: Suppressor of cytokine signaling 3 (SOCS3); non-small cell lung cancer (NSCLC); promoter methylation; treatment response.

Figure 1

Immunohistochemistry was used to assess SOCS3 expression. Representative images of SOCS3 expression in NSCLC samples, demonstrating that this protein is primarily localized to the cytoplasm. Staining method: IHC. Left: low SOCS3 expression; right: high SOCS3 expression. SOCS3, suppressor of cytokine signaling 3; NSCLC, non-small cell lung cancer; IHC, immunohistochemistry.

Figure 2

Representative images of SOCS3 promoter methylation status as analyzed by MSP product electrophoresis. Based on these results, patients 1, 2, 5, and 6 were assigned to the methylated group, while patients 3 and 4 were assigned to the unmethylated group. M, methylated; U, unmethylated; SOCS3, suppressor of cytokine signaling 3; MSP, methylation-specific polymerase chain reaction.

Figure 3

The relationship between SOCS3 expression and promoter methylation status and OS. (A) The relationship between SOCS3 expression and OS; (B) the relationship between SOCS3 promoter methylation and OS. SOCS3, suppressor of cytokine signaling 3; OS, overall survival.

Figure 4

SiRNA-mediated knockdown of SOCS3 (A) enhances JAK2 and STAT3 phosphorylation and the expression of caspase-3 in cultured H1299 and H1437 cells, and is associated with significant increases in the (B) survival rate and (C) drug-induced apoptosis rate of these cells. (D) TUNEL was to assess SOCS3 apoptosis, 200×. *, P<0.05. SOCS3, suppressor of cytokine signaling 3; STAT3, signal transducer and activator of transcription 3; p, phosphorylated; t, total; JAK2, Janus kinase 2; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; si, small-interfering; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling.

Figure 5

JAK2/STAT3 signal pathway mediates SOCS3 to regulate the death of NSCLC cells. (A) The inhibition of JAK2/STAT3 phosphorylation processed with WP1066 (50 mM) dramatically reduced caspase-3 expression in si-SOCS3-transfected lung cancer cells compared to the control cells. WP1066 treatment impaired the pro-survival effects of SOCS3 knockdown in these lung cancer cell lines as evidenced by (B) reductions in the cell survival rate and (C) increases in the cell apoptosis rate. (D) TUNEL was to assess SOCS3 apoptosis, 200×. *, P<0.05. SOCS3, suppressor of cytokine signaling 3; STAT3, signal transducer and activator of transcription 3; p, phosphorylated; t, total; JAK2, Janus kinase 2; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; DMSO, dimethyl sulfoxide; si, small-interfering; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling; NSCLC, non-small cell lung cancer.