M6P/IGF2R modulates the invasiveness of liver cells via its capacity to bind mannose 6-phosphate residues.
Bottom Line: Forced expression of M6P/IGF2R restores intracellular transport of cathepsins to lysosomes and concomitantly reduces the tumorigenicity and invasive potential of these cells.We also demonstrate that functional M6P-binding sites are important for the anti-invasive properties of M6P/IGF2R, whereas the capacity to bind IGF-II is dispensable for the anti-invasive activity of the receptor in liver cells.M6P/IGF2R restricts liver cell invasion by preventing the pericellular action of M6P-modified proteins.
Affiliation: Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.Show MeSH
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Mentions: For permanent receptor knock-down, MIM-1–4 cells were stably transfected with an M6P/IGF2R-specific shRNA construct. Densitometric analysis of immunoblots revealed that the residual receptor content of the two MIM-1–4/IGF2R shRNA clones chosen for further studies was <1% as compared with cells transfected with a control shRNA sequence (Fig. 4A). This goes in hand with enhanced β-N-acetylhexosaminidase secretion, with MIM-1–4/IGF2R shRNA cells (line 1: 55%; line 2: 47%) secreting far more of this lysosomal marker enzyme than parental (7%) and control cells (16%). Similar observations were made for cathepsin D. MIM-1–4/IGF2R shRNA cells secreted substantially more of this lysosomal proteinase (11%) than parental MIM-1–4 cells (1%). The difference in cathepsin L secretion between MIM-1–4/IGF2R shRNA and parental cells was less pronounced (87% and 81%, respectively). NH4Cl treatment resulted in strongly enhanced β-N-acetylhexosaminidase secretion by parental and control MIM-1–4 cells. Conversely, MIM-1–4/IGF2R shRNA cells displayed no further increase in β-N-acetylhexosaminidase secretion upon addition of NH4Cl (Fig. 4B and C).
Affiliation: Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.