The COOH-Terminal Domain of Wild-Type Cot Regulates Its Stability and Kinase Specific Activity

Abstract

Cot, initially identified as an oncogene in a truncated form, is a mitogen-activated protein kinase kinase kinase implicated in cellular activation and proliferation. Here, we show that this truncation of Cot results in a 10-fold increase in its overall kinase activity through two different mechanisms. Truncated Cot protein exhibits a lower turnover rate (half-life, 95 min) than wild-type Cot (half-life, 35 min). The degradation of wild-type and truncated Cot can be specifically inhibited by proteasome inhibitors in situ. The 20S proteasome also degrades wild-type Cot more efficiently than the truncated protein. Furthermore, the amino acid 435 to 457 region within the wild-type Cot COOH-terminal domain confers instability when transferred to the yellow fluorescent protein and targets this fusion protein to degradation via the proteasome. On the other hand, the kinase specific activity of wild-type Cot is 3.8-fold lower than that of truncated Cot, and it appears that the last 43 amino acids of the wild-type Cot COOH-terminal domain are those responsible for this inhibition of kinase activity. In conclusion, these data demonstrate that the oncogenic activity of truncated Cot is the result of its prolonged half-life and its higher kinase specific activity with respect to wild-type Cot.

ACKNOWLEDGMENTS

We thank Dirk Bohmann for providing the pCMV-His-ubiquitin construct, M. F. Balduino Burgering for the HA-PKB-DD and PKB-CaaX constructs, and Blanca Duarte and Nora Perez for their technical help.

This work was supported by CICYT grant SAF 2002-00566 to J.G.C. and BMC2002-00437, AICR, and Fundación La Caixa grants to S.A. M.L.G. was the recipient of a fellowship from the Fundación Marcelino Botin, and P.L. was the recipient of a fellowship from Fundación La Caixa.