KRAS mutation in colorectal cancer and its association with a stromal-derived gene signature.

Abstract

628 Background: KRAS mutation in colorectal cancer (CRC) is characterized by an altered transcriptional profile when compared to wild-type KRAS tumors. The list of differentially expressed genes overlaps significantly with a stromal fibroblast activation (SFA) signature present across multiple carcinomas. We have reported low expression of SFA genes in KRAS mutant CRC compared to KRAS wild type tumors. Here we sought to confirm the variation of the SFA signature with KRAS mutation and infer its origin in the stromal component of the tumor using experimental models. Methods: The SFA signature was assessed in an inducible-KRAS murine CRC model using RNA-sequencing, and in a CRC cell line with and without a transduced KRAS mutant vector by microarray analysis. Finally, RNA-sequencing of CRC patient-derived xenografts (PDXs) was used to determine whether the SFA signature was being expressed in the tumor epithelium or the surrounding stroma by leveraging the ability to align sequenced reads to the mouse and human genomes separately. Results: The SFA signature was identified in the inducible-KRAS mouse model, matching human cohort observations of decreased SFA gene expression in KRAS mutant CRC. On the other hand, KRAS transduction did not recapitulate the SFA signature in a CRC cell line, suggesting that the presence of stroma may be required for the expression of the SFA signature. Finally, RNA-seq reads for SFA signature genes in CRC PDXs immediately after implantation aligned primarily to the human genome but in later passages of the same PDXs aligned only to the mouse genome. These data suggest that the SFA transcriptional program is associated with the stroma rather than the epithelial tumor cells. Conclusions: KRAS mutation in CRC is associated with a gene expression signature derived from the tumor stroma. These findings suggest that KRAS mutation in the epithelial tumor cells may impact the tumor microenvironment in CRC.