A quarter or more of all human cancers have an oncogenic mutation in one of the RAS genes, rendering the encoded protein constitutively active, which promotes tumorigenesis. While oncogenic Ras has so far defied clinical inhibition, studies of signaling through two of its most notorious effectors, RAF and PI3K, have led to new antineoplastic drugs. There is, however, a third major effector of oncogenic Ras involved in cancer that is far less studied, namely RalGEFs that activate the two Ras like GTPases RalA and RalB. Broadly speaking, RalA is important in transformation, tumor initiation, and maintenance whereas RalB plays a more prominent role in cell migration, invasion, and metastasis. This difference in function can be ascribed, at least in part, to an Aurora A phosphorylation site in RalA that is absent in RalB. Moreover, phosphorylation of this site on RalA by Aurora A is critical for oncogenic Ras tumorigenesis, and both high Aurora A expression and RAS mutations occur together in a number of human cancers. Taken together, these results suggest that the combined activation by oncogenic Ras and phosphorylation by up-regulated Aurora A of RalA promotes tumorigenesis. In terms of the underlying mechanism of how these two events drive tumor development, we discovered that activation and phosphorylation of RalA re-localizes the protein with its effector RalBP1 to mitochondria to induce fission. This novel discovery provides the first direct molecular link between Ras oncogenesis through RalA and mitochondrial function during tumorigenesis. To better understand this relationship we propose to determine in aim 1, the mechanism by which RalA is activated to promote fission, in aim 2, what other kinases phosphorylate RalA and the consequences thereof, in aim 3, the mechanism by which RalBP1 induces fission to promote tumorigenesis, and finally in aim 4, the consequence of blocking phosphorylation of endogenous RalA on cancer development in vivo. Completion of these aims will elucidate the molecular mechanism by which RalA signaling promotes mitochondrial fission, and the effect of this signaling on cancer development in vivo.

Public Health Relevance

Ras is mutated in one quarter or more of all human cancers. So far however, the protein has eluded inhibition in a clinical setting. Thus, our studies on determining how mutant Ras transduces its malignant signals have direct significance to cancer, particularly as new targets could be identified to treat Ras-driven cancers.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Cancer Molecular Pathobiology Study Section (CAMP)
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Watson, Joanna M
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Duke University
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Kashatus, Jennifer A; Nascimento, Aldo; Myers, Lindsey J et al. (2015) Erk2 phosphorylation of Drp1 promotes mitochondrial fission and MAPK-driven tumor growth. Mol Cell 57:537-51
Brady, Donita C; Crowe, Matthew S; Turski, Michelle L et al. (2014) Copper is required for oncogenic BRAF signalling and tumorigenesis. Nature 509:492-6
Yang, Shuqun; Counter, Christopher M (2013) Cell cycle regulated phosphorylation of the telomere-associated protein TIN2. PLoS One 8:e71697
Kashatus, David F; Lim, Kian-Huat; Brady, Donita C et al. (2011) RALA and RALBP1 regulate mitochondrial fission at mitosis. Nat Cell Biol 13:1108-15
Issaq, Sameer H; Lim, Kian-Huat; Counter, Christopher M (2010) Sec5 and Exo84 foster oncogenic ras-mediated tumorigenesis. Mol Cancer Res 8:223-31
Lim, Kian-Huat; Brady, Donita C; Kashatus, David F et al. (2010) Aurora-A phosphorylates, activates, and relocalizes the small GTPase RalA. Mol Cell Biol 30:508-23
Zipfel, P A; Brady, D C; Kashatus, D F et al. (2010) Ral activation promotes melanomagenesis. Oncogene 29:4859-64
Naini, Sarasija; Etheridge, Katherine T; Adam, Stacey J et al. (2008) Defining the cooperative genetic changes that temporally drive alveolar rhabdomyosarcoma. Cancer Res 68:9583-8
Adam, Stacey J; Counter, Christopher M (2008) A method to generate genetically defined tumors in pigs. Methods Enzymol 439:39-51
Lim, Kian-Huat; Ancrile, Brooke B; Kashatus, David F et al. (2008) Tumour maintenance is mediated by eNOS. Nature 452:646-9

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