IGFBP-3, a marker of cellular senescence, is overexpressed in human papillomavirus-immortalized cervical cells and enhances IGF-1-induced mitogenesis.
Human ectocervical cells, following retroviral transduction with the human papillomavirus type 16 E6/E7 oncogenes, are altered in their array of transcribed cellular genes, including increased mRNA for the insulin-like growth factor binding protein 3 (IGFBP-3). IGFBP-3 expression is associated with cellular senescence, and its addition to many cell types inhibits growth or induces apoptosis. By immunoblotting and enzyme-linked immunosorbent assay methods, we demonstrate that late-passage, immortalized E6/E7-transduced cells secrete high levels of IGFBP-3 (25 ng/ml), which represent a 500-fold increase compared to levels in early-passage, nonimmortalized transduced cells (<0.05 ng/ml). Concomitantly, these late-passage cervical cells exhibit an increase in sensitivity to IGF-1, including enhanced phosphorylation of the IGF receptor (IGF-R) and insulin receptor substrate as well as increased DNA synthesis (5-fold) and cell proliferation (3.7-fold). However, there was no change in the level of IGF-R in these cells (surface or total), and the cells did not synthesize IGF-1, indicating that these arms of the IGF pathway were independently regulated and not responsible for the augmented signaling. Consistent with a causal relationship between IGFBP-3 expression and enhanced IGF-1 responses, we found that early-passage cells could be converted to the late-passage, IGF-1-responsive phenotype by preincubation with IGFBP-3. Thus, in contrast to findings with some cell types, IGFBP-3 expression in cervical cells is associated with augmented IGF-1 signaling and cell proliferation and correlates with the timing of cellular immortalization.
Baege
Astrid C
AC
Department of Pathology, Georgetown University Medical Center, 3900 Reservoir Rd. NW, Washington DC 20057, USA.
Disbrow
Gary L
GL
Schlegel
Richard
R
D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D016922:Cellular Senescence; D002584:Cervix Uteri / Q000821:virology*; D004247:DNA / Q000096:biosynthesis; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009856:Oncogene Proteins, Viral / Q000235:genetics* / Q000502:physiology; D050725:Papillomavirus E7 Proteins; D017526:Receptor, IGF Type 1 / Q000032:analysis; D012097:Repressor Proteins
C068651:E6 protein, Human papillomavirus type 16; D018972:Insulin-Like Growth Factor Binding Protein 3; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; D007334:Insulin-Like Growth Factor I; D004247:DNA; D017526:Receptor, IGF Type 1