an intestinal lesion, classified as either an intraepithelial neoplasia, an adenocarcinoma or an adenoma. Lung cancer PTPRK mRNA was shown to be significantly reduced by RT-PCR in human lung cancer-derived cell lines. Prostate cancer PTPRK has also been shown to be downregulated in response to androgen stimulation in human LNCaP prostate cancer cells. The mechanism whereby PTPRK is downregulated is via the expression of a microRNA, miR-133b, which is upregulated in response to androgen stimulation. Breast cancer Patients with reduced PTPRK transcript expression have shorter breast cancer survival times and are more likely to have breast cancer metastases or to die from breast cancer. In an experimental model of breast cancer, PTPRK was reduced in breast cancer cell lines with PTPRK ribozymes. In these cells, adhesion to matrigel, transwell migration, and cell growth were all increased following the reduction of PTPRK expression, again supporting a function for PTPRK as a tumor suppressor. Glioma Assem and colleagues identified loss of heterozygosity (LOH) events in malignant glioma specimens, and identified PTPRK as a significant gene candidate in one LOH region. A significant correlation between the presence of PTPRK mutations and short patient survival time was observed. PTPRK was amplified from tumor cDNA to confirm the LOH observed. In these specimens, 6 different mutations were observed, two of which (one in each phosphatase domain) disrupted the enzymatic activity of PTPRK. Expression of wild-type PTPkappa in U87-MG and U251-MG cells resulted in a reduction in cell proliferation, migration and invasion. Expression of the variants of PTPkappa with mutations in the phosphatase domains, however, increased cell proliferation, migration and invasion, supporting a role for the involvement of the mutated variants of PTPkappa in tumorigenicity. In development In situ hybridization localized PTPkappa mRNA to the brain, lung, skeletal muscle, heart, placenta, liver, kidney and intestines during development. PTPkappa was also found to be expressed in the developing retina, in nestin-positive radial progenitor cells and later in development, in the ganglion cell layer, inner plexiform layer and outer segments of photoreceptors. PTPkappa protein is observed in neural progenitor cells and radial glial cells of the developing mouse superior colliculus, as well. In the adult rat brain, PTPkappa mRNA is highly expressed in regions of the brain with cellular plasticity and growth, such as the olfactory bulb, the hippocampus and the cerebral cortex. PTPkappa mRNA is also observed in the adult mouse cerebellum. Using a β-galactosidase (β-gal) reporter