We have used human specimens and
antibodies to pERK1/2 to detect early development of
colon cancer using indirect immunocytochemistry. Two distinct sites were stained; one at the tip of the colon crypts and the other in the stromal tissue associated with the colonic tissue. These foci represent early stages of
colon cancer initiation sites as established by enhanced Kirsten Rat
Sarcoma Virus (KRAS) and the lack of p53 staining. The enhanced KRAS coincides with the initiation of
tumor growth revealed by pERK1/2, both in the tip of the colon crypts, as well as in the stromal initiation site of the colon
tumors. Foci of pERK1/2 staining were also detected in 50% of stromal tissue and
tips of colon crypts, which were classified as normal tissues, adjacent to the malignant tissue according to general morphology. However, in colon specimens, where no
malignancy was observed, no accumulation of pERK1/2 was observed. The staining of pERK1/2 at the stromal foci of the apparently non-malignant tissue appeared as aggregates in the perinuclear region, while in the colon epithelium it appeared in the cell nuclei. In low-grade
colon cancer that was still free of induced mutated p53, staining of pERK1/2 was prominent in the cell nuclei, both in the stroma tissue and the tip of the colon crypts. In the intermediate stage, that exhibited significant p53 staining, only a fraction of p53-free
tumor cells was labeled with pERK1/2 antibody, while in high-grade
tumors, all cells of
tumors were labeled with
antibodies to p53, but not with
antibodies to pERK1/2. We suggest that the down regulation in pERK1/2 labeling is due to the mitogenic capacity of the
tumor cells, which are shifted from being driven by nuclear pERK1/2 to mutated p53 expression. We also found that the cytoplasm of low grade
tumors was positive for
epiregulin, while this labeling decreased in high-grade
tumors. We found that the
tumors arising from the stroma demonstrated poor structural differentiation, while the
tumors initiating from the epithelial cells of the colon demonstrated high structural differentiation. We conclude that pERK1/2 is a sensitive marker of early
colon cancer, which disappears at later stages of
cancer development. Moreover, pERK1/2 staining can distinguish between
tumor cells originating from the tip of the colon crypts and those developing in the stroma, which is present in the close vicinity to colon epithelial tissue, and thus can assist in selecting the appropriate
therapy.