ERK (extracellular signal regulated kinase) is the terminal kinase of the RAS-RAF-MEK-ERK pathway that controls numerous biological processes. Inappropriate ERK activation occurs in many cancers that contain oncogenic driver mutations in RAS, RAF or receptor tyrosine kinases such as EGFR and FGFR. ERK regulates biological processes through phosphorylation of substrate proteins. ERK substrates have been identified through individual gene approaches and more recently through discovery based proteomic approaches, although the functional role of many substrates is not known. We have taken a three part functional genomics approach that identified 30 substrates that function in seven different biological processes in C. elegans germline development: (1) bioinformatically identified candidate substrates that contain ERK docking sites conserved in position with the human ortholog; (2) RNAi tested function of the candidate substrates in ERK dependent biological processes using sensitized genetic backgrounds; (3) validated that the RNAi positive hit as a robust in vitro substrate of mammalian ERK2 and for a subset, demonstrated that ERK dependent phosphorylation occurs in vivo. Three conclusions came from our work: (A) Multiple ERK substrates control individual biological processes; (B) Substrates are molecularly diverse, affecting many parts of the cellular machinery, such as translation, RNA metabolism, cytoskeleton; (3) Substrates function cooperatively to promote a given process. Deregulated proliferation is a key aspect of cancer. The prevailing view from individual gene studies in the mammalian cell culture/cancer field is that RAS-ERK signaling promotes proliferation through transcription factor substrates. However the proteomic discovery and our functional genomic approach indicate that only ~12% of ERK substrates are associated with transcriptional control, the remaining affecting a wide range of cellular machinery. We propose that a number of ERK substrates that mediate proliferation remain to be discovered, particularly gene products that act in non- transcriptional cellular machinery, which can be identified in functional screens. Recently, a RAS-driven, ERK- dependent germline tumor model was reported for C. elegans, which provides an opportunity to identify ERK substrates that promote proliferation. We propose to apply our proven three part functional approach to identify C. elegans proteins, with human orthologs, that are ERK substrates that control proliferation in the RAS-drive, ERK-dependent tumor model. Discovery of ERK substrates with human orthologs will further our understanding of how RAS-ERK signaling promotes proliferation, provide a set of genes to be tested in mammalian cell culture models, may identify genes with cancer associated genomic alterations as ERK substrates, and may provide a framework/specific genes that can be used in cancer therapeutic approaches.
The ERK (extracellular signal regulated kinase) is a member of the RAS-ERK cascade that is often oncogenically activated in cancer. ERK functions by phosphorylation of substrate proteins, however many ERK substrates that contribute to cancer remain to be identified. The proposed studies will identify novel ERK substrates that contribute to cancer, which will provide a deeper understanding of the oncogenic process and may generate new avenues for therapeutic approaches, including cases of acquired resistance to RAS-ERK pathway drug treatment.
