The NF2 tumor suppressor gene product, merlin, inhibits cell proliferation and cell cycle progression by repressing cyclin D1 expression.
Inactivation of the NF2 tumor suppressor gene has been observed in certain benign and malignant tumors. Recent studies have demonstrated that merlin, the product of the NF2 gene, is regulated by Rac/PAK signaling. However, the mechanism by which merlin acts as a tumor suppressor has remained obscure. In this report, we show that adenovirus-mediated expression of merlin in NF2-deficient tumor cells inhibits cell proliferation and arrests cells at G1 phase, concomitant with decreased expression of cyclin D1, inhibition of CDK4 activity, and dephosphorylation of pRB. The effect of merlin on cell cycle progression was partially overridden by ectopic expression of cyclin D1. RNA interference experiments showed that silencing of the endogenous NF2 gene results in upregulation of cyclin D1 and S-phase entry. Furthermore, PAK1-stimulated cyclin D1 promoter activity was repressed by cotransfection of NF2, and PAK activity was inhibited by expression of merlin. Interestingly, the S518A mutant form of merlin, which is refractory to phosphorylation by PAK, was more efficient than the wild-type protein in inhibiting cell cycle progression and in repressing cyclin D1 promoter activity. Collectively, our data indicate that merlin exerts its antiproliferative effect, at least in part, via repression of PAK-induced cyclin D1 expression, suggesting a unifying mechanism by which merlin inactivation might contribute to the overgrowth seen in both noninvasive and malignant tumors.
Xiao
Guang-Hui
GH
Human Genetics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Gallagher
Ryan
R
Shetler
Justin
J
Skele
Kristine
K
Altomare
Deborah A
DA
Pestell
Richard G
RG
Jhanwar
Suresh
S
Testa
Joseph R
JR
D000256:Adenoviridae / Q000235:genetics; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019938:Cyclin D1 / Q000235:genetics* / Q000502:physiology; D015536:Down-Regulation; D020868:Gene Silencing; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D008654:Mesothelioma / Q000235:genetics*; D009154:Mutation / Q000235:genetics; D025581:Neurofibromin 2 / Q000235:genetics / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D014162:Transfection; D054462:p21-Activated Kinases
D025581:Neurofibromin 2; D034741:RNA, Small Interfering; D019938:Cyclin D1; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases
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