The expression of transcription factors TWIST and Snail in breast cancer

Abstract

Breast cancer comprises of 22.9% of all cancers worldwide in females. In the year

2008, it has caused 458,503 deaths worldwide. De-regulation of transcription factors

has been shown to play an important role in the progression of breast cancers.

Snail and TWIST genes have been found to promote epithelial-mesenchymal

transition (EMT). It has been suggested that the level of expression of each of these

genes correlates with poor prognosis in different types of solid tumors. For breast

cancer, the up-regulation of Snail was associated with recurrence and higher tumor

grade, while the up-regulation and up-regulation of TWIST was associated with

shorter survival and metastatic development. However, in recent studies conflicting

results have been observed.

Our collaborator had analyzed mRNA expression data obtained from the Gene

Expression Omnibus (GEO) database together with patient survival data from the

breast cancer cohort datasets, and found that expression of Snail when stratified

against TWIST expression levels or vice versa, gave more significant association with

survival than when expression levels of Snail or TWIST was considered on their own.

To investigate whether these findings could be demonstrated at a protein level, we

performed imrnuno-histochemisty analysis on breast cancer samples in tissue

microarray blocks. Nuclear and cytoplasmic scores of TWIST were successfully

assessed separately in 114 invasive breast cancer patients. The Snail scores were

obtained from previous studies.

As Snail and TWIST are both transcription factors, nuclear expression of each was

examined for correlation of Snail and TWIST with pathological features and patient

survival.

Our results showed that nuclear Snail expression did not correlate with survival

(p=0.498) but when stratified with nuclear TWIST, high levels of nuclear Snail

expression associated with poorer survival in patients with low nuclear TWIST

expression (p=O.2l2), though not statistically significant which agreed with the

mRNA results of our collaborator.

For nuclear TWIST expression, association with survival was in reverse from that of

the mRNA findings. Low expression levels of TWIST mRNA was associated with

shorter survival, however immuno-histochemistry showed that high levels of nuclear

TWIST expression marginally correlated with poorer survival (p=O.079). Low levels

of cytoplasmic TWIST expression on the other hand, correlated with poorer survival

in patients (p=O.024), and when stratified against high nuclear Snail, expression was

associated with shorter survival (p=O.022), which is in keeping with mRNA findings.

The results show that Snail and TWIST expression gave more prognostic value when

considered together than when considered individually, which suggests that Snail and

TWIST might be functionally similar in the promoting of EMT mediated breast. It

also highlights the importance of nuclear and cytoplasmic localization by

immuno-histochemistry in evaluating results and in assessing its role in promoting

breast cancer progression. In conclusion Snail and TWIST should be considered

together for prognostication of breast cancer as they may complement each other in

predicting the progression of the disease.