Cellular distribution of the IGF-1R in corneal epithelial cells

Abstract

This study characterized the expression and subcellular localization of the IGF-1R in human corneal epithelial cells. Using a human telomerase-immortalized corneal epithelial cell line, IGF-1R expression and localization was assayed by immunofluorescence and subcellular fractionation followed by western blot. IGF-1R expression was confirmed in primary cultured human corneal epithelial cells. Nuclear localization was assessed under basal and IGF-1 stimulated culture conditions; phosphorylation status of the receptor in response to IGF-1 was demonstrated by western blot. IGF-1R:E-cadherin interactions were detected by immunofluorescence and co-immunoprecipitation of whole cell lysates. The results of this study demonstrated that IGF-1R localized predominantly to the nucleus and in a perinuclear cap pattern which co-localized with the Golgi complex in proliferating corneal epithelial cells. There was no difference in nuclear localization between primary or telomerized cell lines. Subcellular fractionation confirmed IGF-1Rα- and β-subunit localization in soluble and chromatin-bound nuclear fractions. Neither growth factor withdrawal nor IGF-1 stimulation altered nuclear IGF-1R. At points of cell-cell contact, IGF-1R co-localized with E-cadherin; co-immunoprecipitation assays confirmed the presence of an IGF-1R:E-cadherin complex. Importantly, this is the first report to identify IGF-1R in the nucleus and complexed with E-cadherin at points of cell-cell contact in corneal epithelial cells. Nuclear trafficking appeared to be independent of ligand-mediated events at the plasma membrane. The identification of IGF-1R in the nucleus and complexed with E-cadherin suggests novel regulatory functions outside the canonical ligand-induced endocytosis signaling pathway.

Sodium arsenite represses the expression of myogenin in C2C12 mouse myoblast cells through histone modifications and altered expression of Ezh2, Glp, and Igf-1

“…Indeed, the translocation of Igf-1 into the nuclei has been reported in regenerating human muscle satellite cells, in which Igf-1 protein was detected in the nuclei at 24 hours after the start of regeneration, and then was diffusely expressed in the myofibers after 72 hours (McKay et al, 2008). Other studies have indicated that the Igf-1 receptor (IGF1R) can localize to the nucleus in corneal epithelial cells (Robertson et al, 2012) and in renal and breast cancer cells (Aleksic et al, 2010). Recently, it been shown that nuclear IFG1R functions as a transcriptional co-activator of LEF1/TCF, leading to increases in protein levels of LEF1 target genes (Warsito et al, 2012).…”

Transporters and receptors in the anterior segment of the eye

“…The binding affi nity for IGF-1 in corneal epithelial cells was 4 n m and the presence of specifi c receptors for IGF-1 was shown. In another study, subcellular expression, distribution and localization of IGF-1 receptor in human corneal epithelial cells was demonstated (Figure 4.5a, b) [115]. Simultaneous expression of 135-kDa α -subunits and 95-kDa β -subunits within the nuclear compartment was identifi ed, indicating the presence of full receptor.…”

“…Negative control (NC, bottom row), primary antibody omitted. Scale: 22.5 μ m. Reproduced with permission of [115]. However, at later stages of lens development, TGFB family members have been shown to induce pathological changes in lens epithelial cells.…”

“…Double labeling immunofl uorescence studies with antibody and nuclear counterstaining were used to identify IGF-1 in corneal epithelial cells. Figure 5a, b shows the localization of IGF-1 in nucleus and juxta-nucleus of epithelial cells and also at the cell-cell junctions [115]. Enhanced expression and homeostasis regulation are involved with corneal epithelium [116,117].…”

“…No staining was noted in the negative control which omitted the primary antibodies (not shown ). Reproduced with permission[115].…”