Vascular endothelial growth factor-A and Poly(A) binding protein-interacting protein 2 expression in human head and neck carcinomas: correlation and prognostic significance

Abstract

Vascular endothelial growth factor-A (VEGF-A) has been demonstrated to play an important role in tumour angiogenesis and to influence prognosis in many cancers. However its prognostic value in head and neck squamous cell carcinomas (HNSCCs) remains controversial. Therefore, we investigated the clinical relevance of VEGF-A expression in HNSCCs and analysed whether its expression was associated with PAIP2 protein levels, a VEGF-A mRNA-binding partner that strongly regulates VEGF-A expression in tissue culture. We determined the correlation of VEGF-A and PAIP2 protein levels, quantitatively evaluated in tumour tissue homogenates from 54 patients with HNSCC, to clinicopathological parameters. We showed that VEGF-A expression in HNSCC is correlated to the stage of tumour differentiation (P=0.050) and is an independent prognostic factor for progression-free survival (P=0.001) and overall survival (P=0.0004). In a pharynx carcinoma cell line, we demonstrated by RNA interference that VEGF-A expression is closely controlled by PAIP2. Moreover, in human HNSCCs, VEGF-A expression is significantly correlated to PAIP2 protein levels (P=0.0018). Nevertheless, PAIP2 expression is associated with neither clinicopathological factors nor patient's survival. Our data suggest that, in contrast to PAIP2 protein levels, which are unrelated to tumour prognosis, VEGF-A expression could serve as a prognostic marker in head and neck cancer and may be helpful for targeted therapies.

Figure 1

Univariate survival analysis investigating the impact of clinical stage (A), nodal status (B) or VEGF-A expression (C) on overall survival of patients with head and neck carcinomas. Graph D illustrates the impact of VEGF-A expression on progression-free survival.

Figure 2

Silencing of PAIP2 by RNA interference inhibits VEGF-A expression in a human pharynx carcinoma cell line. (A) Total protein extracts from Detroit 562 cells transiently transfected twice with siRNAs against PAIP2 or GFP, were analysed by Western blotting using a polyclonal anti-PAIP2 antibody. The amounts of ERK2 are shown as a loading control. (B) Total RNA extracted from the same cells was subjected to Northern blotting analysis for VEGF-A mRNA expression (upper panel). The arrows point to the different VEGF-A isoforms. 36B4 RNA is shown as a loading control. The levels of VEGF-A mRNA were quantified by phosphorImaging analysis (lower panel). The values are normalised to 36B4 RNA. Values obtained with the control siRNA are taken as 100%. The data shown represent the means and standard errors of two independent experiments. (C) Tissue culture supernatants from the same cells were analysed using a human VEGF-A specific ELISA. The values are normalised to the cell number. Values obtained with the control siRNA are taken as 100%. The data shown represent the means and standard errors of two independent experiments each performed in triplicate.