Inhibition of Caco-2 cell proliferation by all-trans retinoic acid: role of insulin-like growth factor binding protein-6.
The present study examined the effects of all-trans retinoic acid (tRA) on proliferation and expression of the IGF system in Caco-2 human colon adenocarcinoma cells. tRA inhibited Caco-2 cell proliferation in a dose-dependent manner, with a 40 +/- 2% decrease in cell number observed 48 h after the addition of 1 microM tRA. Ligand blot analysis of IGFBPs in conditioned media revealed that Caco-2 cells produced three IGFBPs of M(r): 34,000 (IGFBP-2), 24,000 (IGFBP-4), and 32,000 (IGFBP-6). The concentrations of IGFBP-2 and IGFBP-4 decreased by 48 +/- 6 and 70 +/- 13%, respectively, whereas that of IGFBP-6 increased by 698 +/- 20% with 1 microM tRA. tRA decreased mRNA levels of IGFBP-2 and IGFBP-4 by 20 +/- 3 and 50 +/- 8%, respectively, whereas tRA increased IGFBP-6 mRNA by 660 +/- 20%. tRA did not alter levels of IGF-II mRNA or peptide. To examine if endogenous IGFBP-6 inhibits cell proliferation, Caco-2 cells were transfected with an IGFBP-6 cDNA expression construct or pcDNA3 vector only and stable clones were selected. Clones overexpressing IGFBP-6 grew more slowly than vector controls and achieved final densities 30-55% lower than those of vector controls. Accumulation of IGFBP-6 mRNA and concentrations of IGFBP-6 peptide in conditioned media were increased by 200-250 and 220-250%, respectively, in the IGFBP-6 clones compared with controls. Increased expression of IGFBP-6, which has a high binding affinity for IGF-II, following tRA treatment suggests that the decreased proliferation caused by tRA may result, at least in part, from IGFBP-6-mediated disruption of the IGF-II autocrine loop in these colon cancer cells.
Kim
Eun J
EJ
Division of Life Sciences, Institute of Environment & Life Science, Hallym University, Chunchon, 200-702, Korea.
Kang
Young-Hee
YH
Schaffer
Beverly S
BS
Bach
Leon A
LA
MacDonald
Richard G
RG
Park
Jung H Y
JH
D018938:Caco-2 Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D017077:Culture Media, Conditioned / Q000737:chemistry / Q000378:metabolism; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015151:Immunoblotting; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics / Q000378:metabolism; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000235:genetics / Q000378:metabolism; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000235:genetics / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II; D008970:Molecular Weight; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology*
D017077:Culture Media, Conditioned; D016895:Culture Media, Serum-Free; D018971:Insulin-Like Growth Factor Binding Protein 2; D018974:Insulin-Like Growth Factor Binding Protein 4; D018976:Insulin-Like Growth Factor Binding Protein 6; D012333:RNA, Messenger; D014212:Tretinoin; D007335:Insulin-Like Growth Factor II