Intranuclear localization of insulin-like growth factor binding protein-3 (IGFBP-3) during cell division in human keratinocytes.
Insulin-like growth factor-I (IGF-I) stimulation of basal keratinocytes is an essential component of normal epidermal homeostasis. In addition to the IGF receptor, basal keratinocytes synthesize insulin-like growth factor binding protein-3 (IGFBP-3). The HaCaT keratinocyte cell line, which has many characteristics of basal keratinocytes, synthesizes IGFBP-3 that in vitro reduces its IGF-I responsiveness. IGFBP-3 has attracted interest as a potential growth arrest protein, both via its ability to modulate IGF-I responsiveness, and more controversially via IGF-I-independent mechanisms. Intracellular modes of action have been proposed, and a nuclear localization consensus sequence has previously been identified within IGFBP-3. Using immunocytochemistry with a biotinylated antibody specific for IGFBP-3, we investigated the intracellular localization of IGFBP-3 in subconfluent monolayer cultures of HaCaT cells. Diffuse cellular staining was visible, potentially corresponding to cell surface and nascent cytoplasmic IGFBP-3. Of particular interest however, was the localization of staining over the nuclei of a large proportion of cells that were undergoing cell division. Antibody staining was specific for IGFBP-3 because addition of recombinant human IGFBP-3 to the antibody prior to incubation with the cells inhibited these staining patterns. Optical sections obtained using a confocal laser scanning microscope showed that in keratinocytes undergoing cell division, IGFBP-3 was localized inside the nucleus. These results show that intracellular IGFBP-3 localization is altered during the cell cycle and suggest a possible nuclear role for IGFBP-3 during cell division.
Center for Hormone Research, Royal Children's Hospital, Parkville, Victoria, Australia.
C J
CJ
Wraight
I J
IJ
Liepe
P J
PJ
White
A R
AR
Hibbs
G A
GA
Werther
D002455:Cell Division; D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000032:analysis*; D015603:Keratinocytes / Q000737:chemistry* / Q000166:cytology
D018972:Insulin-Like Growth Factor Binding Protein 3