SPARC promotes cell invasion in vivo by decreasing type IV collagen levels in the basement membrane

Abstract

Overexpression of SPARC, a collagen-binding glycoprotein, is strongly associated with tumor invasion through extracellular matrix in many aggressive cancers. SPARC regulates numerous cellular processes including integrin-mediated cell adhesion, cell signaling pathways, and extracellular matrix assembly; however, the mechanism by which SPARC promotes cell invasion in vivo remains unclear. A main obstacle in understanding SPARC function has been the difficulty of visualizing and experimentally examining the dynamic interactions between invasive cells, extracellular matrix and SPARC in native tissue environments. Using the model of anchor cell invasion through the basement membrane (BM) extracellular matrix in Caenorhabditis elegans, we find that SPARC overexpression is highly pro-invasive and rescues BM transmigration in mutants with defects in diverse aspects of invasion, including cell polarity, invadopodia formation, and matrix metalloproteinase expression. By examining BM assembly, we find that overexpression of SPARC specifically decreases levels of BM type IV collagen, a crucial structural BM component. Reduction of type IV collagen mimicked SPARC overexpression and was sufficient to promote invasion. Tissue-specific overexpression and photobleaching experiments revealed that SPARC acts extracellularly to inhibit collagen incorporation into BM. By reducing endogenous SPARC, we also found that SPARC functions normally to traffic collagen from its site of synthesis to tissues that do not express collagen. We propose that a surplus of SPARC disrupts extracellular collagen trafficking and reduces BM collagen incorporation, thus weakening the BM barrier and dramatically enhancing its ability to be breached by invasive cells. Author SummarySPARC is an extracellular matrix protein that is present at high levels in many metastatic cancers where it promotes tumor invasion into neighboring tissues. The mechanism linking a surplus of SPARC to cell invasion, however, is not clear due to the challenge of examining SPARCs function in complex tumor environments. We have used anchor cell Data Availability Statement: All relevant data are within the paper and its Supporting Information files.Funding: This study was funded by the Pew Scholars Program in the Biomedical Sciences (DRS), a National Science Foundation Graduate Research Fellowship (MAM), and the National Institute of General Medicine grant GM079320 (DRS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.invasion in C. elegans development to understand how an excess of SPARC promotes invasion in a native tissue setting. Anchor cell invasion allows experimental examination and visualization of the interactions between an invasive cell, neighboring tissues, and the basement membrane, a sheet-like extracellular matrix that surrounds tissues. We find that increased SPARC expression potently enhances the ability of weakly invasive anchor cells to breach the basement membrane. Our data ind...

SPARC acts as a mediator of TGF‐β1 in promoting epithelial‐to‐mesenchymal transition in A549 and H1299 lung cancer cells

“…SPARC contributed to the migration and invasion of human hepatocellular carcinoma . By decreasing type IV collagen levels, SPARC promoted cell invasion in vivo . Therefore, these results suggested that SPARC plays an important role in A549 and H1299 lung cancer cells migration.…”

Collagen-binding byDrosophilaSPARC is essential for survival and for collagen IV distribution and assembly into basement membranes

“…Previous studies have demonstrated a Col(IV) chaperone-like activity of SPARC in invertebrate model organisms (Isabella and Horne-Badovinac, 2015b; Morrissey et al, 2016; Shahab et al, 2015). In this study, we used a hemocyte cell line to determine that SPARC and Col(IV) first colocalize in the trans-Golgi with little or no colocalization within the ER or cis-Golgi.…”

“…Studies in D. melanogaster and C. elegans report that the proper assembly of Col(IV) into BMs is dependent on the presence of SPARC (Secreted Protein Acidic Rich in Cysteine). Moreover, the diffusion of Col(IV) to secondary sites is inhibited by the absence of SPARC (Isabella and Horne-Badovinac, 2015b; Morrissey et al, 2016; Pastor-Pareja and Xu, 2011; Shahab et al, 2015). It is hypothesized that SPARC functions to delay nucleation of Col(IV) polymers upon their secretion to enable proper BM assembly at both the site of production and at distal sites that do not express BM components.…”

α-integrins dictate distinct modes of type IV collagen recruitment to basement membranes

“…In C. elegans, collagen IV is a heterotrimer formed from two α1-like and one α2-like chains, encoded by the emb-9 and let-2 genes respectively 26 . Collagen is predominantly synthesized in body wall muscles, secreted into the extracellular space, and then recruited to the BM of other tissues 14,27 . To understand how type IV collagen is targeted to the BM of growing organs, we examined the BMs of the pharynx and the gonad ( Figure 1A).…”