Summary
Mitogen-activated protein kinase (MAPK) cascades are core pathways mediating cellular responses to
a wide variety of extracellular and intrinsic cues. In the past several years, we have made progress in
understanding how connections are made in MAPK signaling networks, and we have exploited this
knowledge to identify new MAPK substrates and regulators. We plan to extend these studies along two
major lines of research. In the first, we will continue to investigate a role for non-catalytic “docking”
interactions in mediating specificity and signaling output by MAPKs. We have developed yeast-based
screening platforms to define sequence motifs selectively interacting with a conserved docking groove
in the MAPK catalytic domain. We have so far applied these methods to a set of MAPKs including
representatives of three major subfamilies (ERK, p38 and JNK). We plan to investigate novel MAPK
substrates uncovered through these screens, with a focus on crosstalk between JNK and small GTPase
signaling pathways. We further propose to expand our studies to include the remaining understudied
MAPK groups, for which few substrates are known. To understand how selectivity is enforced in MAPK
signaling systems, we will perform structural studies of MAPKs in complex with key regulators
interacting with the docking groove and other ill-defined interfaces. Our second line of inquiry follows
upon our recent discovery of the protein phosphatase 6 (PP6) complex as a MEK phosphatase that
negatively regulates oncogenic ERK signaling. Despite being conserved throughout eukaryotes and
essential to life in mammals, we know very little about the basic architecture and regulation of the
complex. We will investigate the basis for PP6 complex assembly, and we will define how interactions
with the catalytic and associated regulatory subunits confer substrate specificity. Finally, we will explore
a role for PP6 in mediating a negative feedback loop in the ERK signaling pathway. Collectively, our
proposed studies over the next five years will provide important new insight into the function of core
signaling pathways relevant to normal physiology and human disease.