Down-regulation of canonical and up-regulation of non-canonical Wnt signalling in the carcinogenic process of squamous cell lung carcinoma

Abstract

The majority of lung cancers (LC) belong to the non-small cell lung carcinoma (NSCLC) type. The two main NSCLC sub-types, namely adenocarcinoma (AC) and squamous cell carcinoma (SCC), respond differently to therapy. Whereas the link between cigarette smoke and lung cancer risk is well established, the relevance of non-canonical Wnt pathway up-regulation detected in SCC remains poorly understood. The present study was undertaken to investigate further the molecular events in canonical and non-canonical Wnt signalling during SCC development. A total of 20 SCC and AC samples with matched non-cancerous controls were obtained after surgery. TaqMan array analysis confirmed up-regulation of non-canonical Wnt5a and Wnt11 and identified down-regulation of canonical Wnt signalling in SCC samples. The molecular changes were tested in primary small airway epithelial cells (SAEC) and various lung cancer cell lines (e.g. A549, H157, etc). Our studies identified Wnt11 and Wnt5a as regulators of cadherin expression and potentiated relocation of β-catenin to the nucleus as an important step in decreased cellular adhesion. The presented data identifies additional details in the regulation of SCC that can aid identification of therapeutic drug targets in the future.

Figure 1. Level of Wnt signalling molecules in AC and SCC.

Pooled cDNA of 12 AC, 8 SSC samples were targeted to gene expression analysis using a commercially available Taqman array. Four housekeeping genes were used (18S, GAPDH, HPRT1, GUSB). A: Expression profile of AC. Pooled cDNA of autologous normal tissue samples of the same AC patients served as reference. Note the increased level of the canonical Wnt-7b, and the receptor Fzd-3. (For the list of all gene expression changes see Table S1). B: Gene expression levels of SCC. Pooled cDNA of autologous normal tissue samples of the same SCC patients served as reference. Note the upregulation of the non-canonical Wnt5a and the canonical pathway inhibitor Dkk-1, along with increased level of Fzd-10 gene expression. (For the list of all gene expression changes see Table S2). C: Gene expression of SCC compared to AC. Note the increased level of non-canonical Wnts (Wnt5a and Wnt11), several receptors (Fzd-7, -9, -10), a canonical pathway inhibitor (Dkk-1) and an inhibitory receptor (Krm2). (For the list of all gene expression changes see Table S3). D and E: Immunohistochemical staining of primary control (Panel D) and AC (Panel E) tissues for Wnt11. Note the higher Wnt11 expression in the tumours emphasizing the relative nature of the initially identified differences at mRNA level. Images shown are representatives of three independent stainings. F: Wnt11 gene transcription was also measured in an AC (A549) and an SCC (H157) cancer cell line. Note the higher Wnt11 levels in the observed cancer cell lines compared to the normal, non-cancerous pulmonary epithelium (SAEC). The AC cell line showed a more pronounced increase in Wnt11 expression than the SCC cell line. (The results are representative of three independent experiments where the non-cancerous control (SAEC) was derived from three individual donors of different ages).

Figure 2. Effects of Wnt11 and Wnt5a in tumour development.

A: Effects of Wnt11 overexpression and suppression in A549 AC cell line. Gene expression of A549-GFP and A549 treated with control siRNA served as reference, respectively. Note the decreased expression of E-cadherin in Wnt11-A549 (p<0.011), and the increased E-cadherin level following siWnt11 treatment (p<0.006). B: Recombinant Wnt11 treatment of SAEC cultures. Gene expression of untreated control cells was used as reference. Note the concentration dependent “cadherin switch” upon rWnt11 treatment. (Data are representative of five independent experiments where SAEC was used of five individual donors of different ages and sexes). C: Expression of E- and N-cadherin in primary adenocarcinoma lung tissue sample compared to its healthy autologous control pair. Data are representative of the analysis of three independent tissue pairs. D: Recombinant Wnt5a treatment of SAEC cultures. Gene expression of untreated control cells was used as reference. Note the concentration dependent “cadherin switch” upon rWnt5a treatment. (The presented data are representative of five independent experiments where SAEC was used as control of five individual donors of different ages and sexes). E: Invasion assay. The A549 AC cell line that expresses high levels of Wnt11 is more invasive than the H157 SCC cell line with lower expression of Wnt11 (p<0.008). F: Invasion assay. Primary non-cancerous SAEC were treated with 1 µg/ml rWnt11 and rWnt5a for three days prior to the assay. Only the rWnt5a treated SAEC migrated faster than the non-treated control cells. (The results are representative of three independent experiments where SAEC was used from three individual donors of different ages).

Figure 3. Effects of β-catenin inhibition on cadherin gene expression.

Suppression of canonical Wnt signalling in SAEC using 1 µg/ml IWR-1 inhibitor or DMSO as diluent control. Gene expression of non-treated SAEC was used as reference. Note the increased E-cadherin and decreased N-cadherin mRNA expressions. (The results are representative of three independent experiments where SAEC was used from three individual donors of different ages).

Figure 4. Localization of β-catenin. A:

Immunofluorescent staining of SAEC. B: Immunofluorescent staining of normal A549. C: Immunofluorescent staining of Wnt11 overexpressing A549. D: Immunofluorescent staining of H157 monolayer cell cultures. (60x image, red: β-catenin, blue: DAPI). Note the dramatic increase in nuclear localization and the decrease in cellular membrane localization of A549 AC, Wnt11-A549 and H157 SCC cell lines compared to the normal pulmonary epithelium (SAEC). Data presented are representative of three independent experiments. E: Densitometry of immunofluorescent images of SAEC, A549, Wnt-11-A549 and H157 cells. Note the increased nuclear localization of β-catenin particularly in the Wnt11-A549 cell line. (M: cellular membrane, CS: cytosol, N: nucleus).

Figure 5. Predicted molecular pathway interactions during SCC development.