Desensitization of melanoma cells to autocrine TGF-beta isoforms.
Previous studies have suggested that transforming growth factor-beta 1 (TGF-beta1) acts as an autocrine growth inhibitor on normal human melanocytes, while melanoma cells may not respond to this stimulus. The role of other TGF-beta isoforms such as TGF-beta2 and TGF-beta3 remained less well characterized. In the present study, the mRNA and protein levels of all three isoforms of TGF-beta were analyzed in a panel of human melanoma cell lines and in cultures of normal human melanocytes in vitro. Northern analysis showed that the degree of TGF-beta1, -beta2, -beta3 mRNA expression varied considerably in melanoma cells, whereas TGF-beta expression was very low in melanocytes. In melanoma cells, secreted amounts of TGF-beta1 and TGF-beta3 were found increased in comparison to normal melanocytes: 615 pg/ml vs. 118 pg/ml and 193 pg/ml vs. 30 pg/ml (mean values). In addition, low levels of TGF-beta2 were detected (mean value: 28 pg/ml). Although TGF-beta secretion increased, the proliferation of melanoma cells was found to be only moderately inhibited by TGF-beta isoforms, in contrast to its strong antiproliferative effect on normal human melanocytes: - 15%, -11%, and -18% vs. -52%, -46%, and -50% average inhibition at 0.5 ng/ml TGF-beta1, -beta2, and -beta3, respectively. The different efficacy of TGF-beta on melanocyte and melanoma cells was highly significant (P<0.0001); in addition, TGF-beta-dependent growth inhibition of melanoma cells from primary tumors vs. cells from metastases showed a trend for further decreased response for the metastatic populations (P< or = 0.075). Measurements of DNA synthesis revealed even more pronounced differences between melanocytes (-86%, -78%, and -80% inhibition, respectively, for TGF-beta1, -beta2, and -beta3) and melanoma cells (no inhibition). Our data show loss of responsiveness of melanoma cells to the growth-inhibitory function of TGF-beta isoforms but not of melanocytes. Although melanoma cells are not growth-inhibited by all three TGF-beta isoforms, they secrete significantly higher levels of TGF-beta, as compared to melanocytes. The reduced response indicates their escape from TGF-beta surveillance with ongoing tumor progression.
Krasagakis
K
K
Department of Dermatology, University Medical Center Benjamin Franklin, The Free University of Berlin, Germany.
Krüger-Krasagakes
S
S
Fimmel
S
S
Eberle
J
J
Thölke
D
D
von der Ohe
M
M
Mansmann
U
U
Orfanos
C E
CE
D002455:Cell Division / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004273:DNA, Neoplasm / Q000096:biosynthesis; D015870:Gene Expression; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D008544:Melanocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D009362:Neoplasm Metastasis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D006131:Growth Inhibitors; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D004247:DNA