Frequent somatic mutations in MAP3K5 and MAP3K9 in metastatic melanoma identified by exome sequencing

Mitchell S Stark, Susan L Woods, Michael G Gartside, Vanessa F Bonazzi, Ken Dutton-Regester, Lauren G Aoude, Donald Chow, Chris Sereduk, Natalie M Niemi, Nanyun Tang, Jonathan J Ellis, Jeffrey Reid, Victoria Zismann, Sonika Tyagi, Donna Muzny, Irene Newsham, YuanQing Wu, Jane M Palmer, Thomas Pollak, David Youngkin, Bradford R Brooks, Catherine Lanagan, Christopher W Schmidt, Bostjan Kobe, Jeffrey P MacKeigan, Hongwei Yin, Kevin M Brown, Richard Gibbs, Jeffrey Trent, Nicholas K Hayward

We sequenced eight melanoma exomes to identify new somatic mutations in metastatic melanoma. Focusing on the mitogen-activated protein (MAP) kinase kinase kinase (MAP3K) family, we found that 24% of melanoma cell lines have mutations in the protein-coding regions of either MAP3K5 or MAP3K9. Structural modeling predicted that mutations in the kinase domain may affect the activity and regulation of these protein kinases. The position of the mutations and the loss of heterozygosity of MAP3K5 and MAP3K9 in 85% and 67% of melanoma samples, respectively, together suggest that the mutations are likely to be inactivating. In in vitro kinase assays, MAP3K5 I780F and MAP3K9 W333* variants had reduced kinase activity. Overexpression of MAP3K5 or MAP3K9 mutants in HEK293T cells reduced the phosphorylation of downstream MAP kinases. Attenuation of MAP3K9 function in melanoma cells using siRNA led to increased cell viability after temozolomide treatment, suggesting that decreased MAP3K pathway activity can lead to chemoresistance in melanoma.