A protein called NUAK2, which is produced by cancer cells to boost their proliferation, and whose presence in tumours is associated with poor disease prognosis, has been identified as a reason some cancers grow faster than others by University of Toronto researchers.
The team, led by Liliana Attisano, Professor in U of T’s Donnelly Centre for Cellular and Biomolecular Research, showed that blocking NUAK2 slows down cancer cell growth raising hopes that a drug could be developed to treat patients.
“We looked at bladder cancer and found that a subset of patients have high levels of NUAK2 protein in their tumours which also happened to be high-grade tumours,"
said Attisano, who is also a professor in U of T’s Department of Biochemistry.
NUAK2 And YAP/TAZ
Mandeep Gill, a graduate student in Attisano’s lab, first found NUAK2 while looking for a way to block the known cancer-promoting proteins called YAP and TAZ (YAP/TAZ). Highly active in many cancers, YAP/TAZ work by latching onto the DNA to switch on genes that promote cell proliferation.
NUAK2 turned out to be one of the genes that was switched on by YAP/TAZ; and unexpectedly it was found to encode a protein that helps shuttle even more YAP/TAZ into the cell’s nucleus, where the DNA is stored, to further bolster abnormal cell growth.
Because YAP/TAZ are active in many cancers, including the aggressive forms of breast and bladder cancer, the researchers wondered if NUAK2 too was elevated in tumour biopsies taken from patients with bladder cancer. They found that NUAK2 was present at high levels in some of the tumours and that those came from patients whose cancer progressed to a more aggressive type.
Fortunately, the flip side is that when NUAK2 is blocked, YAP/TAZ can no longer enter the nucleus. This keeps YAP/TAZ away from the DNA and breaks the vicious cycle by which cancer reinforces itself.
Targeting The Hippo Pathway
YAP/TAZ belong to the so-called Hippo pathway, a network of proteins that are important for normal cell and tissue growth but which often goes haywire in cancer. The pathway was named after its role in controlling organ size so that organs grow abnormally large, or “hippo-like”, when the pathway breaks down.
Although the Hippo pathway, which normally keeps cell proliferation in check, is inactivated in many cancers, so far there was no good way to target it with drugs. The discovery of NUAK2 changes this.
[caption id=“attachment_97168” align=“aligncenter” width=“680”] NUAK2 phosphorylates and inhibits LATS activity.
a) Purified NUAK2 blocks LATS-mediated phosphorylation of YAP in an in vitro kinase assay. WT wild type, pMOB1A* the modified active variant (T12 to T353) of MOB1A (see Methods). Levels of immunoprecipitated LATS used for a and d are shown (right).
b) A schematic depicting in vitro kinase assay. The method used to produce and activate each component is indicated.
c) NUAK2 phosphorylates the wild-type (WT) but not the T246/S613 double mutant (DM) LATS in an in vitro kinase assay. Levels of immunoprecipitated WT and DM LATS are comparable. Relative phosphorylation levels from blots is quantitated and plotted as the mean ± SD (n = 5) (right). WT* MST-activated WT LATS. Note that the DM mutant migrates as a doublet, similar to MST-activated WT LATS, consistent with the notion that endogenous NUAKs have a reduced ability to block LATS1 activation.
d) NUAK2 does not inhibit the activity of the LATS T246/S613 double mutant (DM) in an in vitro kinase assay.
e) Expression of LATS T246/S613 (DM) induces cytoplasmic localization of YAP in MDA-MB231 cells. Quantitated results are plotted as the mean ± SD (n = 3). Scale bar, 25 μm. N: nuclear, C: cytoplasmic
Credit: Mandeep K. Gill et al, CC-BY[/caption]
By blocking NUAK2 protein, either by drugs or by muting the gene that encodes it, the researchers were able to slow down expansion of breast cancer cells in the dish and to shrink breast tumours in mice, respectively. A similar approach could target high-grade tumours in patients.
“If you check the patient’s tumour and if they have high levels of NUAK2 protein, we could maybe treat them with NUAK2 inhibitors. The ultimate goal is to find a drug that would work on people”
Attisano said. He and his team are currently working to develop the anti-NUAK2 compound into a form in which it can be used on animals to further validate the target.
The work was supported by funds from the Terry Fox Research Institute and by Foundation grants from the Canadian Institute for Health Research and from the Cancer Research Society of Canada.
Mandeep K. Gill, Tania Christova, Ying Y. Zhang, Alex Gregorieff, Liang Zhang, Masahiro Narimatsu, Siyuan Song, Shawn Xiong, Amber L. Couzens, Jiefei Tong, Jonathan R. Krieger, Michael F. Moran, Alexandre R. Zlotta, Theodorus H. van der Kwast, Anne-Claude Gingras, Frank Sicheri, Jeffrey L. Wrana & Liliana Attisano A feed forward loop enforces YAP/TAZ signaling during tumorigenesis Nature Communications volume 9, Article number: 3510 (2018)
Top Image: Mandeep K. Gill et al, CC-BY