A human keratinocyte cell line produces two autocrine growth inhibitors, transforming growth factor-beta and insulin-like growth factor binding protein-6, in a calcium- and cell density-dependent manner.
Two growth inhibitors were identified in culture medium conditioned by a human keratinocyte cell line, HaCat. TGF-beta was detected in media conditioned by growing or confluent HaCat cells, as well as in media conditioned at physiological (1 mM) or low (0.03 mM) Ca2+ concentrations. However, a considerable part of transforming growth factor beta (TGF-beta) in media conditioned at a physiological Ca2+ concentration was in active form, whereas most TGF-beta in media conditioned at a low Ca2+ concentration was latent. The other growth-inhibitory activity, which was detected only in media conditioned by confluent cells at a physiological Ca2+ concentration, was purified to homogeneity by a four-step procedure. The N-terminal amino acid sequence of the 33-kDa protein was identical with that of insulin-like growth factor binding protein-6 (IGFBP-6). Purified IGFBP-6 inhibited the growth of HaCat and Balb/MK keratinocyte cell lines, as well as Mv1Lu cells. The growth activity was also demonstrated by human recombinant IGFBP-6. In summary, HaCat cells secrete at least two possible autocrine growth inhibitors: TGF-beta which is secreted constitutively, but activated in a Ca(2+)-dependent manner, and IGFBP-6 which is secreted in a cell density- and Ca(2+)-dependent manner.
Kato
M
M
Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
Ishizaki
A
A
Hellman
U
U
Wernstedt
C
C
Kyogoku
M
M
Miyazono
K
K
Heldin
C H
CH
Funa
K
K
D000595:Amino Acid Sequence; D002118:Calcium / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D017077:Culture Media, Conditioned; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D018976:Insulin-Like Growth Factor Binding Protein 6; D015603:Keratinocytes / Q000187:drug effects / Q000502:physiology*; D008969:Molecular Sequence Data; D012867:Skin / Q000166:cytology; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology
D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D007328:Insulin; D018976:Insulin-Like Growth Factor Binding Protein 6; D016212:Transforming Growth Factor beta; D002118:Calcium