Retinoic acid alters the intracellular trafficking of the mannose-6-phosphate/insulin-like growth factor II receptor and lysosomal enzymes

Abstract

Previously, we showed that retinoic acid (RA) binds to the mannose-6-phosphate͞insulin-like growth factor II receptor (M6P͞IGF2R) with high affinity, suggesting that M6P͞IGF2R may be a receptor for RA. Here, we show that RA, after 2-3 h of incubation with cultured neonatal-rat cardiac fibroblasts, dramatically alters the intracellular distribution of M6P͞IGF2R as well as that of cathepsin B (a lysosomal protease bearing M6P). Immunof luorescence techniques indicate that this change in intracellular distribution is characterized by a shift of the proteins from the perinuclear area to cytoplasmic vesicles. The effect of RA was neither blocked by an RA nuclear receptor antagonist (AGN193109) nor mimicked by a selective RA nuclear-receptor agonist (TT-NPB). Furthermore, the RA-induced translocation of cathepsin B was not observed in M6P͞IGF2R-deficient P388D1 cells but occurred in stably transfected P388D1 cells expressing the receptor, suggesting that the effect of RA might be the result of direct interaction with M6P͞IGF2R, rather than the result of binding to the nuclear receptors. These observations not only support the idea that M6P͞IGF2R mediates an RAresponse pathway but also indicate a role for RA in control of intracellular trafficking of lysosomal enzymes. Therefore, our observations may have important implications for the understanding of the diverse biological effects of retinoids.The mannose-6-phosphate͞insulin-like growth factor II receptor (M6P͞IGF2R) is a 300-kDa multifunctional transmembrane glycoprotein. Recently, this receptor has been shown to play a fundamental role in the control of cell growth in fetal development (1-3) and carcinogenesis (4-10).M6P͞IGF2R is primarily (90-95%) localized in the intracellular compartments, particularly in the trans-Golgi network (TGN) and endosomes, with 5-10% of the receptor present on the cell surface (11). The primary function of M6P͞IGF2R is to sort and transport M6P-bearing glycoproteins from TGN to endosomes͞lysosomes (11). Normally, the newly synthesized soluble lysosomal enzymes are posttranslationally modified to contain M6P residues on their N-linked oligosaccharides. The acquired M6P residues enable the enzymes to bind to M6P receptors in the TGN. The receptors and their ligands cluster into clathrin-coated transport vesicles and travel to an acidic prelysosomal compartment where the low pH causes dissociation of the receptor-ligand complex. The free M6P receptors can travel to the plasma membrane or back to the TGN to reinitiate another cycle of biosynthetic enzyme transport. In

M6P/IGF2R is mutated in squamous cell carcinoma of the lung

“…In contrast, receptor down-regulation in choriocarcinoma cells by antisense M6P/IGF2R RNA increases both tumor cell growth rate and tumorigenicity (O'Gorman et al, 1999). The M6P/IGF2R also contains a retinoic acid (RA) bind site (Kang et al, 1997), and receptor overexpression in RA-resistant cancer cells lacking functional RA nuclear receptors confers susceptibility to RA-induced apoptosis (Kang et al, 1999). The results of these functional studies, coupled with frequent M6P/IGF2R mutation in a number of human cancers, demonstrate the importance of this genetic target in human carcinogenesis.…”

“…Evidence to date suggests, however, that the M6P/ IGF2R is not involved in cell signaling (Korner et al, 1995); this function is mediated primarily by the insulin-like growth factor I receptor (IGFIR) and the insulin receptor isoform A (Czech et al, 1989;Frasca et al, 1999). The M6P/IGF2R has also been shown to be mutated in a number of human cancers, including those that develop in the liver, breast and colon (Jirtle et al, 1999b), and to suppress cancer cell growth (Kang et al, 1999;O'Gorman et al, 1999;Souza et al, 1999). These ®ndings are consistent with the M6P/ IGF2R functioning normally as a tumor suppressor.…”

The secreted glycoprotein CREG inhibits cell growth dependent on the mannose-6-phosphate/insulin-like growth factor II receptor

“…Since the M6P/IGF2R is well characterized as a trafficking receptor whose activities include intracellular transport to lysosomes, localization of proteins at the cell surface, and internalization of extracellular ligands (Kang et al, 1998;Blanchard et al, 1999;Godar et al, 1999;Jadot et al, 1999), we investigated the possibility that the M6P/IGF2R might be important for CREG localization. Previous immunofluorescence studies of transiently transfected CREG showed predominant staining of overexpressed CREG in the ER and Golgi (Veal et al, 2000).…”

Retinoic acid inhibits the infectivity and growth of Chlamydia pneumoniae in epithelial and endothelial cells through different receptors

“…TTNPB is an agonist of ATRA, which binds to the RAR nuclear receptor, but not the M6P/IGF-2 receptor at the host cell surface, and thus, can be used to differentiate effects of ATRA that result from binding to the M6P/IGF2 receptor or RAR receptor (12). Therefore, these results indicated that ATRA inhibited binding of C. pneumoniae to the M6P/IGF2 receptor [8].…”

“…Binding of ATRA to the cellular M6P/IGF2 receptor affects binding of the phosphomannosylated residues and alters intracellular trafficking of the M6P/IGF2 receptor and its ligands [12]. In addition, ATRA has anti-oxidant properties and can elicit a variety of cellular responses affecting cell growth, differentiation, and metabolism [13,14] and interfere with glycosylation of viral proteins [15].…”