bioRxiv preprint doi: https://doi.org/10.1101/2021.03.25.436925; this version posted March 25, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. The endosome is a master regulator of plasma membrane collagen fibril assembly 1Joan Chang*, 1Adam Pickard, 1Richa Garva, 1Yinhui Lu, 2Donald Gullberg and 1Karl E. Kadler* 1Wellcome Centre for Cell-Matrix Research, Faculty of Biology, Medical and Health, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT UK, 2Department of Biomedicine and Center for Cancer Biomarkers, Norwegian Center of Excellence, University of Bergen, Norway. * Co-corresponding authors: JC email:
[email protected] (orcid.org/0000-0002-7283- 9759); KEK email:
[email protected] (orcid.org/0000-0003-4977-4683) Keywords: collagen-I, endocytosis, extracellular matrix, fibril, fibrillogenesis, integrin-a11, trafficking, VPS33b, [abstract] [149 word max] Collagen fibrils are the principal supporting elements in vertebrate tissues. They account for 25% of total protein mass, exhibit a broad range of size and organisation depending on tissue and stage of development, and can be under circadian clock control. Here we show that the remarkable dynamic pleomorphism of collagen fibrils is underpinned by a mechanism that distinguishes between collagen secretion and initiation of fibril assembly, at the plasma membrane. Collagen fibrillogenesis occurring at the plasma membrane requires vacuolar protein sorting (VPS) 33b (which is under circadian clock control), collagen-binding integrin-a11 subunit, and is reduced when endocytosis is inhibited. Fibroblasts lacking VPS33b secrete soluble collagen without assembling fibrils, whereas constitutive over-expression of VPS33b increases fibril number with loss of fibril rhythmicity.