Abstract
The insulin-like growth factor-I receptor (IGF-IR), plays a key role in regulating mammalian development and growth, and is frequently deregulated in cancer contributing to tumor initiation and progression. Discoidin domain receptor 1 (DDR1), a collagen receptor tyrosine-kinase, is as well frequently overexpressed in cancer and implicated in cancer progression. Thus, we investigated whether a functional cross-talk between the IGF-IR and DDR1 exists and plays any role in cancer progression.Using human breast cancer cells we found that DDR1 constitutively associated with the IGF-IR. However, this interaction was enhanced by IGF-I stimulation, which promoted rapid DDR1 tyrosine-phosphorylation and co-internalization with the IGF-IR. Significantly, DDR1 was critical for IGF-IR endocytosis and trafficking into early endosomes, IGF-IR protein expression and IGF-I intracellular signaling and biological effects, including cell proliferation, migration and colony formation. These biological responses were inhibited by DDR1 silencing and enhanced by DDR1 overexpression.Experiments in mouse fibroblasts co-transfected with the human IGF-IR and DDR1 gave similar results and indicated that, in the absence of IGF-IR, collagen-dependent phosphorylation of DDR1 is impaired.These results demonstrate a critical role of DDR1 in the regulation of IGF-IR action, and identify DDR1 as a novel important target for breast cancers that overexpress IGF-IR.
Highlights
The type I IGF-I receptor (IGF-insulin receptors (IR)) binds with high affinity both insulin like growth factors I and II (IGF-I and IGF-II), and has a crucial role in the regulation of mammalian development and growth [1,2,3]
In order to determine whether Discoidin domain receptor 1 (DDR1) may functionally interact with the IGF-I receptor (IGF-IR), we first evaluated by immunoblot DDR1 and IGF-IR expression in a panel of IGF-I-responsive human breast cancer cell lines (MCF-7, T47D, ZR-75, MDA-MB-157, MDA-MB-231, BT-474), and in human HepG2 hepatoblastoma cells
MCF-7 and T47D showed the highest IGF-IR levels while the lowest levels were detected in MDAMB-231 and BT-474
Summary
The type I IGF-I receptor (IGF-IR) binds with high affinity both insulin like growth factors I and II (IGF-I and IGF-II), and has a crucial role in the regulation of mammalian development and growth [1,2,3]. We have previously demonstrated that IR-A associates with discoidin domain receptors (DDRs) after IGF-II stimulation [13]. DDRs are membrane receptor tyrosine-kinases (RTKs) that bind to and are activated by various forms of collagen, and include two family members, DDR1 and DDR2, which are encoded by different genes [14, 15]. DDR1 is the better characterized in this respect It interacts at tyrosine 513 with the PTB domain of ShcA [17], and with several other molecules, including the tyrosine phosphatase Shp-2, the adapter protein Nck, and the regulatory subunit of phosphatidyl-inositol-3 kinase, p85 [18]. High affinity binding to collagen requires DDR1 dimerization [19, 20], but a percentage of DDR1 molecules may dimerize in ligandindependent manner [21]
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