SMAD4 protein expression and cell proliferation in colorectal adenocarcinomas

Adriana Handra-Luca, Sylviane Olschwang, Jean-François Fléjou

The TGFβ signalling pathway is a growth inhibitor system that operates in both normal and tumour cells. Alterations to components of this pathway, including SMAD4, result in resistance to growth inhibition and uncontrolled proliferation. The aim of this study was to analyse the relationships between SMAD4, a key protein in the growth-inhibiting TGFβ pathway; cell proliferation proteins Ki67, p27 and S-phase kinase-associated protein 2 (SKP2); and mismatch repair (MMR) proteins as well as prognostic indicators in colorectal adenocarcinomas. A series of 230 sporadic colorectal adenocarcinomas were studied using tissue microarrays by immunohistochemistry for SMAD4, Ki67, p27, SKP2 and MMR protein (hMLH1, hMSH2 and hMSH6) expression. Protein expression was analysed with respect to pathological prognostic criteria. Loss of SMAD4 nuclear expression (27/230, 12%) correlated with the presence of lymph node metastases, MMR protein expression and the absence of p27 in tumour cells (p = 0.04, p = 0.08 and p = 0.03, respectively). A high Ki67 index did not correlate with SMAD4 expression; however, it did correlate with moderate or poor histological differentiation, SKP2 expression and aberrant or absent MMR protein expression (p = 0.02, p < 0.01 and p < 0.01, respectively). In conclusion, the results of our study suggest that the loss of SMAD4, occurring in 12% of colorectal adenocarcinomas, correlated with the presence of lymph node metastases and absence of p27 expression but not with high cellular proliferation. However, high proliferation correlated with SKP2 and aberrant MMR protein expression. Although the advantage of immunohistochemistry is high throughput, our results allow only an initial evaluation, and subsequent studies, including genetic analyses, are required.