CKAP2-DT

We used DNA microarray screening to identify Ckap2 (cytoskeleton associated protein 2) as a novel p53 target gene in a mouse erythroleukemia cell line. DNA damage induces human and mouse CKAP2 expression in a p53-dependent manner and p53 activates the Ckap2 promoter. Overexpressed Ckap2 colocalizes with and stabilizes microtubules. In p53-null cells, overexpression of Ckap2 induces tetraploidy with aberrant centrosome numbers, suggesting disturbed mitosis and cytokinesis. In p53-competent cells, Ckap2 does not induce tetraploidy but activates p53-mediated cell cycle arrest and apoptosis. Our data suggest the existence of a functional positive feedback loop in which Ckap2 activates the G1 tetraploidy checkpoint and prevents aneuploidy.

We performed differential-display polymerase chain reaction to find up-regulated sequences in primary human gastric cancers, and cloned one up-regulated sequence, which was expressed in all the gastric cancer cells that we examined. The cloned sequence was identified as cytoskeletal-associated protein 2 (CKAP2). We also cloned a shorter splice variant, CKAP2-s. The CKAP2 or CKAP2-s protein in HeLa cells was localized to microtubule organizing centers (MTOC) and microtubules. This co-localization pattern was disrupted by nocodazole, a microtubule-destabilizing agent.

These observations suggested that CKAP2 might be associated with microtubule networks. CKAP2 protein was detected in neither normal GI tract nor normal gastric mucosa. However, both CKAP2 and CKAP2-s mRNAs were up-regulated in 55% (23 out of 42 samples) of primary human gastric cancers by reverse transcriptase-polymerase chain reaction (RT-PCR). Moreover, CKAP2 proteins were detected in immunohistochemical staining in all the gastric cancer samples that we examined. CKAP2 protein-expressing cells were also found in gastric adenomas. The average number of CKAP2 protein-positive cells in adenocarcinomas was 48.8%, which was significantly higher than the number in tubular adenomas, 9.1%.

When these points were taken together, we concluded that CKAP2 is up-regulated in primary human gastric adenocarcinomas at high frequency and might be useful for diagnosing and discriminating adenocarcinomas from tubular adenomas of the stomach.