Growth hormone induces tyrosyl phosphorylation of the transcription factors Stat5a and Stat5b in CMT-U335 canine mammary tumor cells.
It has now been well documented that the normal and tumorous canine mammary glands can be extra-pituitary sites of substantial growth hormone (GH) synthesis. Until now, attempts to reproduce the GH synthesis in-vitro using canine mammary explants or mammary tumor cells have not been successful. Therefore, the response of CMT-U335 canine mammary tumor cells to administered porcine GH (pGH) was investigated as an in-vitro model to study the possible effects of GH synthesis on this site. CMT-U335 cells spontaneously express the growth hormone receptor (GHR) as well as the prolactin receptor (PRLR). Twenty five minutes after administration, GH induced, in a dose-dependent manner, phosphorylation of the transcription factors Stat5a and Stat5b. Clear phosphorylation was induced by 10(-7) M and 10(-8) M pGH, with virtually no phosphorylation at 10(-9) M pGH. A similar dose-dependent phosphorylation of Stat5a by ovine prolactin was found in these cells. Although at high concentrations binding of pGH to the canine PRLR can occur (albeit with a low pKa), the similar dose-dependent effect of oPRL on Stat5a phosphorylation indicated that pGH signaled through the GHR. Remarkably, pGH induced a moderately decreased proliferation of CMT-U335 tumor cells, which may indicate that GH induces differentiation in these tumor cells. The GH-induced activation of Stat5a and Stat5b in these cells, as part of the JAK/Stat signal transduction pathway, is consistent with mammary GH playing a role in autocrine and/or paracrine stimulation of (tumorous) mammary cells.
van Garderen
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E
Department of Pathology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, The Netherlands. e.vangarderen@vet.uu.nl
Swennenhuis
J F
JF
Hellmén
E
E
Schalken
J A
JA
D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004285:Dogs; D015870:Gene Expression; D013006:Growth Hormone / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D015674:Mammary Neoplasms, Animal / Q000378:metabolism*; D008894:Milk Proteins; D008969:Molecular Sequence Data; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism*; D011388:Prolactin / Q000494:pharmacology; D012313:RNA / Q000032:analysis; D011981:Receptors, Prolactin / Q000737:chemistry / Q000235:genetics; D050799:STAT5 Transcription Factor; D017385:Sequence Homology; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011981:Receptors, Prolactin; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494095:STAT5B protein, human; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; D019000:Phosphotyrosine; D012313:RNA; D011388:Prolactin; D013006:Growth Hormone