12-O-tetradecanoylphorbol-13-acetate inhibits melanoma growth by inactivation of STAT3 through protein kinase C-activated tyrosine phosphatase(s).
The growth of most melanoma cells in vitro is inhibited by the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). In this study, the involvement of the signal transducer and activator of transcription 3 (STAT3) in the TPA-induced growth inhibition of melanoma cells was examined. The in vitro growth and DNA synthesis of five melanoma cell lines, whose STAT3 was activated (phosphorylated), was inhibited by TPA, whereas that of WM35 and WM39 cells, whose STAT3 activity was at negligible levels, was considerably slow and not affected by TPA. Blockade of STAT3 activity by small interfering RNAs suppressed the growth of WM1205Lu cells containing constitutively activated STAT3. Treatment of WM1205Lu cells with TPA decreased both the phosphorylated STAT3 and the DNA-binding activity of STAT3. Pretreatment of WM1205Lu cells with either a protein-tyrosine phosphatase inhibitor or a protein kinase C (PKC) inhibitor prevented the inhibitory effects of TPA on the level of phosphorylated STAT3. The five melanoma cell lines containing phosphorylated STAT3 commonly expressed PKCalpha, PKCdelta, and PKCepsilon. Introduction of the dominant negative mutant of one of these PKC isoforms into WM1205Lu cells inhibited the TPA-induced dephosphorylation of STAT3. A Src inhibitor attenuated the STAT3 phosphorylation in WM1205Lu cells. These results indicate that constitutively activated STAT3 is positively regulated by c-Src and negatively regulated by a PKC-activated tyrosine phosphatase(s) in melanoma cells. Because TPA did not affect c-Src activity, we conclude that the growth inhibitory effect of TPA on melanoma cells is mediated through inactivation of STAT3 by a PKC-activated tyrosine phosphatase(s).
Oka
Masahiro
M
Division of Dermatology, Department of Internal Related, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan. oka@med.kobe-u.ac.jp
Sumita
Naoko
N
Sakaguchi
Masanobu
M
Iwasaki
Tetsushi
T
Bito
Toshinori
T
Kageshita
Toshiro
T
Sato
Ken-ichi
K
Fukami
Yasuo
Y
Nishigori
Chikako
C
D000970:Antineoplastic Agents / Q000494:pharmacology; D000081247:CSK Tyrosine-Protein Kinase; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D004247:DNA / Q000378:metabolism; D006801:Humans; D008545:Melanoma / Q000188:drug therapy* / Q000473:pathology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D019061:src-Family Kinases
D000970:Antineoplastic Agents; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor; D004247:DNA; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D011493:Protein Kinase C; D017027:Protein Tyrosine Phosphatases; D013755:Tetradecanoylphorbol Acetate