Alpha B-crystallin is a new prognostic marker for laryngeal squamous cell carcinoma

A total of one hundred and nine cases of LSCC were collected from the Department of Pathology, the Affiliated Hospital of Nantong University between 2000 and 2009. Diagnosis of LSCC was determined according to the latest WHO criteria[15] and TNM stage classification (UICC 2002). Among the cases, there were 107 men and 2 women. The mean age of patients at the time of surgery was 60.8 years (ranging from 29 to 87 years). Related clinical data were collected, including gender, age, tobacco and alcohol consumption, tumor differentiation, pTNM stage, lymph node metastasis, and 5-year follow-up survival. Follow-up in all patients started from post-operation of May 2010. None of the 109 patients had performed radiotherapy, chemotherapy or immunotherapy before the surgery. Study protocol was approved by the Ethics Committee of Jiangsu Province Official Hospital.

Six samples of fresh LSCC tissues and their adjacent tissues were collected from the Department of Otolaryngology-Head and Neck Surgery, the Second Affiliated Hospital of Nanjing Medical University and the Department of Otolaryngology-Head and Neck Surgery, Yiji Shan Hospital of Wannan Medical College. Total RNA was extracted from LSCC tissues and tumor-adjacent tissues by using Trizol reagent (Invitrogen, Carlsbad, CA) according to the manufacturer's protocol. RNA (2 μg) was reverse transcribed using High-Capacity cDNA Archive Kit (Promega) in accordance with the manufacturer's protocols. Primers were as follows: αB-crystallin forward 5’-CTTTGACCAGTTCTTCGGAG-3’, reverse 5’-CCTCAATCACATCTCCCAAC-3’; β-actin forward 5’- CTCCATCCTGGCCTCGCTGT-3’, reverse 5’- GCTGCTACCTTCACCGTTCC-3’. The transcription levels of β-actin served as a loading control. Analysis of qPCR was performed using SYBR green dye in an ABI PRISM 7000HT Sequence Detection System (Applied Biosystems, Foster City, CA, USA) following the manufacturer’s instructions. Cycle conditions were as follows: after an initial incubation at 50°C for 2-min and at 95°C for 10 min, the samples were cycled 40 times at 95°C for 15 seconds and 56°C for 1 min.

Formalin-fixed, paraffin-embedded tissues from 109 LSCC and 28 tumor-adjacent normal tissues were prepared and utilized in this present study. TMA was produced by Xinchao Biotech (Shanghai, China). Core tissue biopsies (2 mm in diameter) were taken from individual paraffin-embedded LSCC and arranged in the new recipient paraffin blocks. Tissue microarray was cut into 4-μm sections and placed on super frost charged glass microscope slides.

Paraffin tissue sections (4 μm) were deparaffinized in 100% xylene and re-hydrated in descending ethanol series and water according to standard protocols. Heat-induced antigen retrieval was performed in 10 mM citrate buffer for 2 min at 100°C. Endogenous peroxidase activity was blocked by hydrogen peroxidase (3%) in Tris-buffered saline (TBS) for 30 min. Then the sections were boiled for 10 min in citrate buffer for antigen retrieval. Nonspecific binding was blocked by incubation with 5% goat serum in TBS for 30 min. Tissue sections were incubated with mouse anti-αB-crystallin antibody (Stressgen, Victoria, Canada; 1:300) in TBS containing 1% bovine serum albumin for 1 h. After washing, sections were incubated with EnVision goat anti-mouse/horseradish peroxidase antibody (EB-2305, ZhongShan, Godbridge, China; 1:2000) for 1 h. The replacement of the primary antibody with PBS served as negative controls. Finally, the sections were developed with 3,3-diaminobenzidine (DAB) chromogen solution and counterstained with hematoxylin. Four fields in each slide were randomly selected and counted, and the percentage of positive staining was determined by two clinical pathologists independently using immunohistochemistry score (IHS)[16]. When a conclusion differed, the final decision was made by consensus. The results were analyzed according to the method described previously[17]. Briefly, IHS was determined by the evaluation of both staining density and intensity. The percentage of positive tumor cells was scored as follows: 1 (0-10% positive cells), 2 (11-50% positive cells), 3 (51-80% positive cells), 4 (81-100% positive cells); and the intensity of staining was scored as follows: 0 (negative), 1 (weakly positive), 2 (moderately positive), and 3 (strongly positive). Multiplication of the intensity and the percentage scores gave rise to the ultimate IHS: a sum score below 3 indicated low expression of αB-crystallin, and a sum score above 4 indicated high expression of αB-crystallin.

The relationship between αB-crystallin expression and clinicopathological factors was analyzed by chi-square test. Survival rate was estimated by Kaplan-Meier method. Univariate and multivariate analysis was carried out using Cox’s proportional hazards regression models. For all tests, the significance level for statistical analysis was set at P < 0.05. Statistical analyses were performed using STATA Version 12.0 (Stata Corporation, College Station, TX).

RT-PCR amplicons were detected by 1.5% agarose gel electrophoresis, confirming that αB-crystallin was expressed in LSCC tissues (Figure 1). Moreover, mRNA levels of αB-crystallin in LSCC tissues and tumor-adjacent tissues were determined by qPCR. Normalized to β-actin, αB-crystallin mRNA level in LSCC tissues (n = 6) and tumor-adjacent normal tissues (n = 6) was 6.808 ± 1.781 and 2.475 ± 0.757, respectively (t = 5.484, P = 0.001). mRNA level of αB-crystallin was significantly higher in LSCC than in tumor-adjacent normal tissues (Figure 2).

By immunohistochemistry analysis, we observed more positive staining cells and stronger staining in LSCC tissues than in tumor-adjacent normal tissues (Figure 3). The positive staining was localized mainly in the cytoplasm of the tumor cells and strong staining was not observed in the surrounding tumor-adjacent areas. Positive staining of αB-crystallin was detected in 64 (58.72%) of 109 LSCC samples, while only 5 cases of 28 tumor-adjacent normal tissues (17.86%) displayed high expression of αB-crystallin. There was significant difference in high expression rate of αB-crystallin between LSCC tissues and normal non-cancerous tissues (P = 0.001).

Correlations between various clinicopathological characteristics and αB-crystallin expression in LSCC tissues were evaluated by χ² test (Table 1). The result showed that high expression of αB-crystallin in LSCC was significantly related to alcohol consumption (P = 0.022), tumor differentiation (P = 0.007), pTNM stage (P = 0.041) and 5-year survival (P = 0.030). However, no statistically significant correlation was found between αB-crystallin expression and gender, age, tobacco use, or lymph node metastasis.

Univariate analysis showed that the life span of LSCC patients was correlated with αB-crystallin expression (P = 0.010), pTNM stage (P < 0.001), lymph node metastasis (P < 0.001) and tumor differentiation (P = 0.022). Multivariate analysis with the Cox regression model indicated that αB-crystallin protein level may serve as an independent prognostic factor for overall survival (P = 0.013) (Table 2). Furthermore, pTNM stage (P = 0.027) and lymph node metastasis (P = 0.015) were identified as independent predictive factors for poor outcome of LSCC. Kaplan-Meier survival curves showed that patients with high αB-crystallin expression had a shorter survival time than patients with low αB-crystallin expression (Figure 4). Kaplan-Meier survival curves demonstrated that patients with high αB-crystallin expression, advanced pTNM stage of LSCC and lymph node metastasis had a significantly shorter survival time.