title: Conservation of protein abundance patterns reveals the regulatory architecture of the EGFR-MAPK pathway.
abstract: Various genetic mutations associated with cancer are known to alter cell signaling, but it is not clear whether they dysregulate signaling pathways by altering the abundance of pathway proteins. Using a combination of RNA sequencing and ultrasensitive targeted proteomics, we defined the primary components-16 core proteins and 10 feedback regulators-of the epidermal growth factor receptor (EGFR)-mitogen-activated protein kinase (MAPK) pathway in normal human mammary epithelial cells and then quantified their absolute abundance across a panel of normal and breast cancer cell lines as well as fibroblasts. We found that core pathway proteins were present at very similar concentrations across all cell types, with a variance similar to that of proteins previously shown to display conserved abundances across species. In contrast, EGFR and transcriptionally controlled feedback regulators were present at highly variable concentrations. The absolute abundance of most core proteins was between 50,000 and 70,000 copies per cell, but the adaptors SOS1, SOS2, and GAB1 were found at far lower amounts (2000 to 5000 copies per cell). MAPK signaling showed saturation in all cells between 3000 and 10,000 occupied EGFRs, consistent with the idea that adaptors limit signaling. Our results suggest that the relative stoichiometry of core MAPK pathway proteins is very similar across different cell types, with cell-specific differences mostly restricted to variable amounts of feedback regulators and receptors. The low abundance of adaptors relative to EGFR could be responsible for previous observations that only a fraction of total cell surface EGFR is capable of rapid endocytosis, high-affinity binding, and mitogenic signaling.
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Tujin
authors.initials: T
authors.lastname: Shi
authors.affiliation: HMS LINCS Center and Laboratory of Systems Pharmacology, Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Mario
authors.initials: M
authors.lastname: Niepel
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Jason E
authors.initials: JE
authors.lastname: McDermott
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Yuqian
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Carrie D
authors.initials: CD
authors.lastname: Nicora
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: William B
authors.initials: WB
authors.lastname: Chrisler
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352 USA.
authors.forename: Lye M
authors.initials: LM
authors.lastname: Markillie
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Vladislav A
authors.initials: VA
authors.lastname: Petyuk
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352 USA.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Smith
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Karin D
authors.initials: KD
authors.lastname: Rodland
authors.affiliation: HMS LINCS Center and Laboratory of Systems Pharmacology, Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Peter K
authors.initials: PK
authors.lastname: Sorger
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Wei-Jun
authors.initials: WJ
authors.lastname: Qian
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352 USA. steven.wiley@pnnl.gov.
authors.forename: H Steven
authors.initials: HS
authors.lastname: Wiley
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D009363:Neoplasm Proteins; C512478:EGFR protein, human; D066246:ErbB Receptors; D020929:Mitogen-Activated Protein Kinase Kinases