Increased mRNA expression of the receptor-like protein tyrosine phosphatase α in late stage colon carcinomas

The protein tyrosine phosphatase α (PTPα) mRNA level in paired samples of late stage (Dukesʹ D) colorectal tumors and adjacent normal colon mucosa was quantified by RNase protection assays. After normalization against 18S RNA or β-actin mRNA level, a 2–10-fold increase in PTPα mRNA was detected in 10 of 14 tumors (~ 70%) compared to mucosa. In situ hybridization of digoxigenin-labelled antisense PTPα RNA to tumor and mucosa sections produced a signal only in neoplastic cells of the tumor sample, consistent with the high increase in PTPα mRNA detected by RNase protection assays of some of the tumors. This is the first report suggesting an association of a protein tyrosine phosphatase with colorectal carcinoma. PTPα is a receptor-like PTP thought to be involved in regulating cell proliferation. Its oncogenic properties when overexpressed in cultured fibroblasts suggest that PTPα overexpression could contribute to the tumorigenic process in colon carcinoma.