Altered p53 Functionality in Cancer-Associated Fibroblasts Promotes Cancer Growth

Introduction: p53 is a seminal tumor suppressor protein, acting as a major barrier against cancer. So far, p53 research has focused primarily on its cell-autonomous functions. Yet, p53 can also exert non-cell-autonomous effects on tumor development. Within the tumor microenvironment, cancer cells surrounded with non-cancerous adjacent cells. Specifically, Cancer-Associated Fibroblasts (CAFs) contribute in multiple ways to tumor progression. To identify the possible roles of p53 in CAFs, we investigated the contribution of p53 to the gene expression landscape and the biological properties of CAFs, relative to normal fibroblasts (NFs). Cancerous mutations in the TP53 gene, resulting in the production of mutant p53 proteins, can lead not only to loss of its tumor suppressive functions, but often also to gain of tumor-promoting activities, associated with altered p53-dependent transcriptional programs. Of note, alterations in the regulatory networks that impinge on p53 may cause genetically wild type (wt) p53 to acquire features resembling bona fide mutant p53. However, the extent and functional impact of p53 conversion from its canonical tumor suppressive state into such “pseudomutant” states in actual human tumors remains to be determined.

Materials and Methods: For co-culture experiments, mCherry-expressing H460 cells and GFP-expressing fibroblasts were seeded together. These co-cultures were subjected to Fluorescent Activated Cell Sorting (BD biosciences ®). Live cell imaging was performed with a DeltaVision microscope ®. CAFs and NFs from the non-cancerous margins, were isolated. It was approved by the local ethics committee and informed consent was obtained from the patients.

Results and Discussion: Global transcriptome analysis displayed substantial differences in the transcriptional impact of p53 between CAFs and NFs. Functional studies revealed that CAF p53, while remaining genetically wt, contributes to the activated fibroblast phenotype of CAFs and promotes non-cell-autonomously tumor cell migration and invasion. Furthermore, the cancer-promoting role of CAF p53 was confirmed by co-injection of fibroblasts and tumor cells into SCID mice. Remarkably, co-cultivation with cancer cells rendered the transcriptional impact of NF p53 more similar to that of CAF p53.

Conclusions:

1. The transcriptional program driven by p53 is drastically altered in CAFs.
2. CAF p53 contributes cancer cell migration and invasion in vitro and tumor growth in vivo.
3. Cancer cells drive rewiring of fibroblast wtp53 to a cancer-promoting state.