title: CDK2 phosphorylation of Smad2 disrupts TGF-beta transcriptional regulation in resistant primary bone marrow myeloma cells.
abstract: Resistance to growth suppression by TGF-beta1 is common in cancer; however, mutations in this pathway are rare in hematopoietic malignancies. In multiple myeloma, a fatal cancer of plasma cells, malignant cells accumulate in the TGF-beta-rich bone marrow due to loss of both cell cycle and apoptotic controls. Herein we show that TGF-beta activates Smad2 but fails to induce cell cycle arrest or apoptosis in primary bone marrow myeloma and human myeloma cell lines due to its inability to activate G(1) cyclin-dependent kinase (CDK) inhibitors (p15(INK4b), p21(CIP1/WAF1), p27(KIP1), p57(KIP2)) or to repress c-myc and Bcl-2 transcription. Correlating with aberrant activation of CDKs, CDK-dependent phosphorylation of Smad2 on Thr(8) (pT8), a modification linked to impaired Smad activity, is elevated in primary bone marrow myeloma cells, even in asymptomatic monoclonal gammopathy of undetermined significance. Moreover, CDK2 is the predominant CDK that phosphorylates Smad2 on T8 in myeloma cells, leading to inhibition of Smad2-Smad4 association that precludes transcriptional regulation by Smad2. Our findings provide the first direct evidence that pT8 Smad2 couples dysregulation of CDK2 to TGF-beta resistance in primary cancer cells, and they suggest that disruption of Smad2 function by CDK2 phosphorylation acts as a mechanism for TGF-beta resistance in multiple myeloma.
authors.affiliation: Department of Pathology, Weill Medical College of Cornell University, New York, NY 10065, USA.
authors.forename: Linda B
authors.initials: LB
authors.lastname: Baughn
authors.forename: Maurizio
authors.initials: M
authors.lastname: Di Liberto
authors.forename: Ruben
authors.initials: R
authors.lastname: Niesvizky
authors.forename: Hearn J
authors.initials: HJ
authors.lastname: Cho
authors.forename: David
authors.initials: D
authors.lastname: Jayabalan
authors.forename: Joseph
authors.initials: J
authors.lastname: Lane
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.forename: Selina
authors.initials: S
authors.lastname: Chen-Kiang
mesh_terms: D017209:Apoptosis; D001854:Bone Marrow Cells / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D009101:Multiple Myeloma / Q000378:metabolism*; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D051899:Smad2 Protein / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: C497782:SMAD2 protein, human; D051899:Smad2 Protein; D016212:Transforming Growth Factor beta; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2