Cancer-associated fibroblasts (CAFs), represent a pivotal compartment of solid
cancers (desmoplasia), and are causatively implicated in
cancer development and progression. CAFs are recruited by
growth factors secreted by
cancer cells and they present a myofibroblastic phenotype, similar to the one obtained by resident fibroblasts during wound healing. Paracrine signaling between
cancer cells and CAFs results in a unique
protein expression profile in areas of desmoplastic reaction, which is speculated to drive
metastasis. In an attempt to decipher large-scale proteomic profiles of the
cancer invasive margins, we developed an in vitro coculture model system, based on
tumor-host cell interactions between
colon cancer cells and CAFs. Proteomic analysis of
conditioned media derived from these cocultures coupled to mass spectrometry and bioinformatic analysis was performed to uncover myofibroblastic signatures of the
cancer invasion front. Our analysis resulted in the identification and generation of a desmoplastic
protein dataset (DPD), consisting of 152 candidate
proteins of desmoplasia. By using monoculture exclusion datasets, a secretome algorithm and gene-expression meta-analysis in DPD, we specified a 22-protein "myofibroblastic signature" with putative importance in the regulation of
colorectal cancer metastasis. Of these
proteins, we investigated
collagen type XII by immunohistochemistry, a
fibril-associated collagen with interrupted triple helices (FACIT), whose expression has not been reported in desmoplastic lesions in any type of
cancer.
Collagen type XII was highly expressed in desmoplastic stroma by and around alpha-smooth muscle actin (α-SMA) positive CAFs, as well as in
cancer cells lining the invasion front, in a small cohort of
colon cancer patients. Other stromal markers, such as
collagen type III, were also expressed in stromal
collagen, but not in
cancer cells. In a complementary fashion, gene expression meta-analysis revealed that COL12A1 is also an upregulated gene in
colorectal cancer. Our proteomic analysis identified previously documented markers of
tumor invasion fronts and our DPD could serve as a pool for future investigation of the tumor microenvironment.
Collagen type XII is a novel candidate marker of myofibroblasts, and/or
cancer cells undergoing dedifferentiation.