Human cancer cells express Slug-based epithelial-mesenchymal transition gene expression signature obtained in vivo

Abstract

Background: The biological mechanisms underlying cancer cell motility and invasiveness remain unclear, although it has been hypothesized that they involve some type of epithelial-mesenchymal transition (EMT).

Methods: We used xenograft models of human cancer cells in immunocompromised mice, profiling the harvested tumors separately with species-specific probes and computationally analyzing the results.

Results: Here we show that human cancer cells express in vivo a precise multi-cancer invasion-associated gene expression signature that prominently includes many EMT markers, among them the transcription factor Slug, fibronectin, and α-SMA. We found that human, but not mouse, cells express the signature and Slug is the only upregulated EMT-inducing transcription factor. The signature is also present in samples from many publicly available cancer gene expression datasets, suggesting that it is produced by the cancer cells themselves in multiple cancer types, including nonepithelial cancers such as neuroblastoma. Furthermore, we found that the presence of the signature in human xenografted cells was associated with a downregulation of adipocyte markers in the mouse tissue adjacent to the invasive tumor, suggesting that the signature is triggered by contextual microenvironmental interactions when the cancer cells encounter adipocytes, as previously reported.

Conclusions: The known, precise and consistent gene composition of this cancer mesenchymal transition signature, particularly when combined with simultaneous analysis of the adjacent microenvironment, provides unique opportunities for shedding light on the underlying mechanisms of cancer invasiveness as well as identifying potential diagnostic markers and targets for metastasis-inhibiting therapeutics.

Figure 1

Color-coded scatter plots for the coexpression of the EMT inducing transcription factor Slug (SNAI2) The scatter plots indicate the strong co-expression with the main signature genes COL11A1 and THBS2, as well as the continuity of the passing of cancer cells through a Slug-based EMT in solid tumors, and the total absence of the co-expression of these genes otherwise. A, B and C, plots from three solid tumor datasets. D, plot from a leukemia dataset.

Figure 2

Color-coded scatter plots in human and mouse of the 18 samples for Slug expression The expression of the EMT inducing transcription factor Slug (SNAI2) is shown in terms of the expression of the main signature genes COL11A1 and THBS2. A, demonstration that this co-expression is present in the xenografted human cells. B, demonstration that this co-expression is absent in the peritumoral mouse cells. C, Bar diagram indicating that other EMT inducing transcription factors are not co-expressed.

Figure 3

Quantitative PCR Shown is the expression of human COL11A1 (A) or mouse COL11A1 (B) in RNA samples isolated from tumor NGP xenografts (number indicated). Expression of human COL11A1 increased in samples from left to right consistent with microarray results. Data were normalized to the expression of human HPRT. Mouse COL11A1 was not expressed in samples. Data was normalized to the expression of mouse Actb. Graphs depicted as relative levels of human (A) or mouse (B) control reference RNA.

Figure 4

Heat map combining human and mouse genes. The 29 human genes include many EMT factors and were found to be significantly co-expressed in the cancer cells.