STAT3-independent inhibition of lysophosphatidic acid-mediated upregulation of connective tissue growth factor (CTGF) by cucurbitacin I.
Cucurbitacins are recognised as anti-tumour agents because of their interference with STAT3 signalling, but may also affect the integrity of the actin cytoskeleton. In the present study the effect of cucurbitacin I was investigated in fibroblasts. In these cells, cucurbitacin I interfered with lysophosphatidic acid (LPA) signalling. It inhibited tyrosine phosphorylation of focal adhesion proteins and induction of connective tissue growth factor (CTGF), a potent profibrotic protein. Inhibition of Src family kinases with PP2, but not the inactive analogue PP3, also interfered with LPA-mediated tyrosine phosphorylation and induction of CTGF. Jak2-STAT3 signalling seemed to be the connecting link, because CTGF induction was sensitive to AG490, an inhibitor of Jak2, and cucurbitacin I, an inhibitor of Jak2 and STAT3. However, LPA did not activate tyrosine phosphorylation of STAT3. Furthermore, cucurbitacin I was as effective in STAT3 knock out cells as in control cells. Therefore, the inhibitory effect of cucurbitacin I was not related to inhibition of STAT3. Immunocytochemical analysis of cucurbitacin I-treated cells revealed disassembly of F-actin fibres, reorganisation into F-actin patches and resolution of focal adhesions. The phenotypic changes resembled changes observed after treatment of the cells with cytochalasin D, which has been shown to interfere with CTGF induction. Concentrations of cucurbitacin I, which have been shown to target Jak2-STAT3 signalling, thus, profoundly affect the actin cytoskeleton and may therefore modulate cell morphology, migration, adherence and gene expression also in non-tumour cells.
Graness
Angela
A
Department of Nephrology and Hypertension, University of Erlangen-Nuremberg, Loschgestrasse 8, D-91054 Erlangen, Germany.
Poli
Valeria
V
Goppelt-Struebe
Margarete
M
D000199:Actins / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002461:Cell Line, Transformed; D055513:Connective Tissue Growth Factor; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D008246:Lysophospholipids / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D008297:Male; D051379:Mice; D050796:STAT3 Transcription Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014315:Triterpenes / Q000494:pharmacology*; D020032:Tyrphostins / Q000494:pharmacology; D015854:Up-Regulation; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
D000199:Actins; D000970:Antineoplastic Agents; C526318:CCN2 protein, mouse; D004338:Drug Combinations; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D008246:Lysophospholipids; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D014315:Triterpenes; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; D055513:Connective Tissue Growth Factor; D019061:src-Family Kinases; C032881:lysophosphatidic acid; C038106:cucurbitacin I