Evidence that the inhibition of TE85 human bone cell proliferation by agents which stimulate cAMP production may in part be mediated by changes in the IGF-II regulatory system.
Our previous studies have shown that insulin-like growth factor-II (IGF-II) is an important autocrine/paracrine regulator of human bone cell proliferation. In this study, we sought to look at the regulation of IGF-II production by human bone cells since IGF-II synthesis is a key variable that regulates the actions of IGF-II at a local site of bone. For studies of IGF-II regulation, we used TE85 human osteosarcoma cells as a model system since these cells exhibited several characteristics which are similar to that of untransformed normal human bone cells. In this study, we investigated the effects of agents which increase intracellular cAMP (forskolin, isobutylmethyl xanthine and prostaglandin E2) and N6,O2' dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) on the IGF-II regulatory system. It was found that these agents caused an increase in the production of an IGFBP in TE85 cells. Subsequent studies on the purification and characterization of IGFBP from DBcAMP treated TE85 cell conditioned medium revealed that the IGFBP produced by TE85 cells in response to DBcAMP treatment was identical to that of 25 kDa inhibitory IGFBP (now designated as IGFBP-4) purified from TE89 human bone cells based on: 1) N-terminal amino acid sequence, 2) amino acid composition, 3) molecular weight and 4) inhibitory actions on basal and IGF-II induced bone cell proliferation. In addition, forskolin and DBcAMP also caused a dose dependent decrease in the production of IGF-II. Consistent with these results, DBcAMP and agents which increase intracellular cAMP inhibited TE85 cell proliferation in a dose dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
Mohan
S
S
Dept of Biochemistry, Loma Linda University, CA.
Baylink
D J
DJ
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000595:Amino Acid Sequence; D001842:Bone and Bones / Q000166:cytology* / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000502:physiology; D002455:Cell Division / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D015232:Dinoprostone / Q000494:pharmacology; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4; D007335:Insulin-Like Growth Factor II / Q000502:physiology*; D008969:Molecular Sequence Data; D012516:Osteosarcoma; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D018974:Insulin-Like Growth Factor Binding Protein 4; D005576:Colforsin; D003994:Bucladesine; D007335:Insulin-Like Growth Factor II; D000242:Cyclic AMP; D015232:Dinoprostone; D015056:1-Methyl-3-isobutylxanthine