title: Functional genomic screen identifies novel mediators of collagen uptake.
abstract: Tissue fibrosis occurs when matrix production outpaces matrix degradation. Degradation of collagen, the main component of fibrotic tissue, is mediated through an extracellular proteolytic pathway and intracellular pathway of cellular uptake and lysosomal digestion. Recent studies demonstrate that disruption of the intracellular pathways can exacerbate fibrosis. These pathways are poorly characterized. Here we identify novel mediators of the intracellular pathway of collagen turnover through a genome-wide RNA interference screen in Drosophila S2 cells. Screening of 7505 Drosophila genes conserved among metazoans identified 22 genes that were required for efficient internalization of type I collagen. These included proteins involved in vesicle transport, the actin cytoskeleton, and signal transduction. We show further that the flotillin genes have a conserved and central role in collagen uptake in Drosophila and human cells. Short hairpin RNA-mediated silencing of flotillins in human monocyte and fibroblasts impaired collagen uptake by promoting lysosomal degradation of the endocytic collagen receptors uPARAP/Endo180 and mannose receptor. These data provide an initial characterization of intracellular pathways of collagen turnover and identify the flotillin genes as critical regulators of this process. A better understanding of these pathways may lead to novel therapies that reduce fibrosis by increasing collagen turnover.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA 94158 Department of Medicine, University of California, San Francisco, San Francisco, CA 94158 Lung Biology Center, University of California, San Francisco, San Francisco, CA 94158 Department of Pathology, University of California, San Francisco, San Francisco, CA 94158 MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom.
authors.forename: Ting-Hein
authors.initials: TH
authors.lastname: Lee
authors.forename: William
authors.initials: W
authors.lastname: McKleroy
authors.forename: Amin
authors.initials: A
authors.lastname: Khalifeh-Soltani
authors.forename: Stephen
authors.initials: S
authors.lastname: Sakuma
authors.forename: Stanislav
authors.initials: S
authors.lastname: Lazarev
authors.forename: Kirsi
authors.initials: K
authors.lastname: Riento
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Nishimura
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Nichols
authors.forename: Kamran
authors.initials: K
authors.lastname: Atabai
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D055785:Gene Knockdown Techniques; D049750:Genome, Insect; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; C106354:flotillins; D003094:Collagen