Survivin gene-expression and splicing isoforms in oral squamous cell carcinoma

Abstract

Purpose: Survivin, an inhibitor of apoptosis protein and a cell cycle regulator, has been detected in the majority of human cancers. Five splice variants (survivin, survivin-2alpha, survivin-2B, survivin-3B, and survivin-DeltaEx3) have been identified; their expressions have been investigated here.

Methods: By means of RT real-time PCR and immunohistochemistry, we have evaluated survivin isoform expressions at both mRNA and protein levels in human normal oral tissue, precancerous lesions, and oral squamous cell carcinoma (OSCC). Their correlations with the pathological findings have also been analyzed.

Results: Expression levels of all survivin transcript variants were markedly elevated in OSCC when compared to normal tissues. One-way analysis of variance (ANOVA) revealed highly significant up-regulation of survivin (P = 0.001), survivin-DeltaEx3 (P = 0.001) and survivin-2B (P = 0.004), whereas survivin-3B showed a minor increase in OSCC compared to normal mucosa.

Conclusions: Our findings suggest that survivin isoforms deregulation may have significant implications in tumor aggressiveness and prognosis.

Fig. 1

Survivin protein expression evaluated by immunohistochemistry; a representative case of OSCC showing overexpression of survivin in almost all tumor cells. Note that non-neoplastic epithelium close to tumor is negative (LSAB–HRP, ×200, nuclear counterstaining with hematoxylin)

Fig. 2

Survivin isoforms in oral cancer; survivin and its splice variants, levels of mRNA expression in 22 cases of OSCC

Fig. 3

Quantitative deregulation of survivin RNA splicing in oral carcinogenesis. Real-time PCR analysis of RNAs isolated from pathological samples representative of different step of oral carcinogenesis compared to matched normal mucosa. Svv survivin, Svv∆Ex3 survivin with exon-3 deletion, Svv2B survivin endowed with an additional 2B exon derived from an intron 2-sequence translocation, Svv3B survivin with an additional 3B exon containing a stop codon, OSCC oral squamous cell carcinoma, Dysplasia cases of oral pre-malignant lesion with histologically ascertained dysplasia, and LN Mets cases of lymph node metastases from OSCC. (P < 0.05)

Fig. 4

Relative quantitative ratios between survivin (Svv) and minor survivin isoforms (∆Ex3, 2B, 3B) in human normal oral mucosa and pathological tissues. Ratio = 2 ^{isoformCt − Svv Ct}. Fold change refers to 2^ΔCt change of Svv expression in relation to isoform expression. Svv survivin, Svv∆Ex3 survivin with exon-3 deletion; Svv2B survivin endowed with an additional 2B exon derived from an intron 2-sequence translocation, Svv3B survivin with an additional 3B exon containing a stop codon, NORMAL normal oral mucosa, OSCC oral squamous cell carcinoma, Dysplasia cases of oral pre-malignant lesion with histologically ascertained dysplasia, and LN Mets cases of OSCC lymph node metastases