Prolactin induces c-Myc expression and cell survival through activation of Src/Akt pathway in lymphoid cells.
Stimulation of resting W53 cells (lymphoid murine cells expressing prolactin (PRL) receptor) by PRL induced expression of growth-related immediate-early genes (IEG), and proliferation through activation of the Src kinases. Since IEG are essential for cell cycle progression, we have studied how PRL controls expression of c-Myc mRNA and c-Fos. Stimulation of W53 cell proliferation by PRL required activation of MAPK, as the Mek1/2 inhibitor PD184352 eliminated Erk1/2 stimulation, cell proliferation, and expression of c-Fos mRNA. In contrast, PD184352 did not alter PRL activation of c-Myc mRNA expression or stimulation of p70S6K, Akt, and the Jak2/Stat5 pathway. Activation of the PI3K by PRL was necessary for the expression of c-MycmRNA and W53 cell proliferation, as the PI3K inhibitor LY294002 abolished them. However, it did not modify PRL stimulation of c-Fos mRNA expression or activation of Erk1/2 and Stat5. Furthermore, rapamycin, an inhibitor of mTOR and consequently of p70S6K, did not alter PRL stimulation of c-Myc and c-Fos mRNA expression and it had a very minor inhibitory effect on PRL stimulation of W53 cell proliferation. In addition, rapamycin did not affect PRL stimulation of Akt or Stat5. However, it reinforced PRL activation of Erk1/2. Overexpression of a constitutively activated Akt (myristoylated Akt) in W53 cells overcame the inhibitory effect of LY294002 on c-Myc expression, as well as cell death upon PRL deprivation. Consistently, inducible expression of Akt-CAAX Box in W53 cells caused inhibition of c-Myc expression. PRL stimulation of W53 cells resulted in Akt translocation to the nucleus, phosphorylation of FKHRL1 transcription factor, and its nuclear exclusion. In contrast, induced expression of Akt-CAAX Box caused inhibition of FKHRL1 phosphorylation. Furthermore, transient expression of nonphosphorylatable FKHRL1-A3 mutant impaired PRL-induced activation of the c-Myc promoter. Akt activation also resulted in phosphorylation and inhibition of glycogen synthetase kinase 3 (GSK3), which in turn promoted c-Myc stability. Consistently, treatment of W53 with selective inhibitors of GSK3 such as SB415286 and lithium salts resulted in increased levels of c-Myc. Also, overexpression of c-Myc in W53 cells overcame the decrease in cell proliferation induced by LY294002. These findings defined a PRL-signalling cascade in W53 cells, involving Src kinases/PI3K/Akt/FKHRL1-GSK3, that mediates stimulation of c-Myc expression.
Domínguez-Cáceres
María Aurora
MA
Instituto de Investigaciones Biomédicas, CSIC, Calle Arturo Duperier, 4, Madrid 28029, Spain.
García-Martínez
José Manuel
JM
Calcabrini
Annarica
A
González
Lorena
L
Porque
Pedro González
PG
León
Javier
J
Martín-Pérez
Jorge
J
D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017781:Genes, Immediate-Early / Q000235:genetics; D016259:Genes, myc / Q000187:drug effects* / Q000235:genetics; D016391:Genes, src / Q000502:physiology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011388:Prolactin / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics
D004791:Enzyme Inhibitors; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D011388:Prolactin; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; C494918:AKT1 protein, human