Kinase Domain Mutation Causes Protein Malfunction and Tumor Development

A team of chemical biologists has generated the first molecular map of the protein doublecortin kinase like domain 1 (DCLK1), a factor linked to more than 10% of gastric cancers that has also been found in kidney, rectal, and pancreatic cancers.

Doublecortin (DCX) is a microtubule-associated protein required for neuronal migration to the cerebral cortex. DCLK1 consists of an N-terminus that is 65% similar to DCX throughout the entire length of DCX, but also contains an additional 360 amino acid C-terminal domain encoding a protein kinase. The homology to DCX suggested that DCLK1 may regulate microtubules, as well as mediate a phosphorylation-dependent signal transduction pathway.

Purified DCLK1 associates with microtubules and stimulates polymerization of purified tubulin and the formation of aster-like microtubule structures. Overexpressed DCLK1 leads to striking microtubule bundling in cell lines and cultured primary neural cells. DCLK1 also encodes a functional kinase capable of phosphorylating myelin basic protein and itself. However, elimination of the kinase activity of DCLK1 has no detectable effect on its microtubule polymerization activity. While DCLK1 is among the 15 most common putative driver genes for gastric cancers and is highly mutated across various other human cancers, how DCLK1 dysfunction leads to tumor development is not well understood.

Investigators at the Walter and Eliza Hall Institute (Parkville, Australia) worked with the Australian Synchrotron to generate the crystal structure of the DCLK1 kinase domain at 1.7 angstrom resolution. This structure, which was published in the August 18, 2016, online edition of the journal Structure, provided detailed insight into the ATP-binding site that is expected to serve as a framework for future drug design. This structure also allowed for the mapping of cancer-causing mutations within the kinase domain, suggesting that a loss of kinase function may contribute to tumor development.

Senior author Dr. Isabelle Lucet, chemical biology laboratory head at the Walter and Eliza Hall Institute, said, "We can think of the kinase domain of DCLK1 being an inbuilt controlling unit for the protein. The kinase domain sits separately from the part of the protein that assembles microtubules, and can switch microtubule assembly on or off as needed. The complexity of having these two different components in one protein has, until now, hindered our understanding of how DCLK1 functions normally and what goes wrong in cancer. We decided to focus on just the regulatory kinase domain of DCLK1, because we knew that this is the part of DCLK1 that is often altered in cancers."

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Walter and Eliza Hall Institute