Targeting of SMAD5 links microRNA-155 to the TGF-beta pathway and lymphomagenesis.
The mechanisms by which microRNA dysfunction contributes to the pathogenesis of diffuse large B cell lymphoma (DLBCL) are not well established. The identification of the genes and pathways directly targeted by these small regulatory RNAs is a critical step to advance this field. Using unbiased genome-wide approaches in DLBCL, we discovered that the oncogenic microRNA-155 (miR-155) directly targets the bone morphogenetic protein (BMP)-responsive transcriptional factor SMAD5. Surprisingly, we found that in DLBCL a noncanonical signaling module linking TGF-beta1 signals to SMAD5 is also active. In agreement with these data, miR-155 overexpression rendered DLBCLs resistant to the growth-inhibitory effects of both TGF-beta1 and BMPs, via defective induction of p21 and impaired cell cycle arrest. In confirmatory experiments, RNAi-based SMAD5 knockdown recapitulated in vitro and in vivo the effects miR-155 overexpression. Furthermore, in primary DLBCLs, miR-155 overexpression inhibited SMAD5 expression and disrupted its activity, as defined by individual and global analyses of its transcriptional targets. Together, our data helped explain miR-155 function, highlighted a hitherto unappreciated role of SMAD5 in lymphoma biology, and defined a unique mechanism used by cancer cells to escape TGF-beta's growth-inhibitory effects.
Division of Hematology and Medical Oncology, Department of Medicine, University of Texas Health Science Center, San Antonio, TX 78229, USA.
Deepak
D
Rai
Sang-Woo
SW
Kim
Morgan R
MR
McKeller
Patricia L M
PL
Dahia
Ricardo C T
RC
Aguiar
D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D006801:Humans; D016403:Lymphoma, Large B-Cell, Diffuse / Q000235:genetics / Q000378:metabolism*; D035683:MicroRNAs / Q000378:metabolism*; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051902:Smad5 Protein / Q000378:metabolism*; D018709:Statistics, Nonparametric; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D019485:Bone Morphogenetic Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; C524942:MIRN155 microRNA, human; D035683:MicroRNAs; D051902:Smad5 Protein; D016212:Transforming Growth Factor beta