The effect of TGFbeta1 on the expression and phosphorylation of key cell-cycle regulators in malignant B cells.
BACKGROUND
Transforming growth factor beta1 (TGFbeta1) induces growth arrest in many cell types, including B lymphocytes. The inhibitory action of TGFbeta1 is mediated by the deactivation of kinase complexes. The cell-cycle engine is tightly controlled by cyclin-dependent kinase (cdk) inhibitors, which mediate extracellular negative signals, resulting in cell-cycle arrest at different G1 points.


METHODS
Our experimental DoHH2 cell line model was derived from a patient with malignant non-Hodgkin's lymphoma (NHL) of follicular origin. We examined the effect of TGFbeta1 on the expression and phosphorylation of key cell-cycle regulators by immunoprecipitation and immunoblotting.


RESULTS
After 48 hours of TGFbeta1 (10 ng/ml) treatment, a significantly increased number of DoHH2 cells was retained in G0/G1 phase. Our results showed the inhibitory action was associated with hypophosphorylation of pRb on serine 795 (S795) and threonine 373 (T373). We examined the composition of the cdk complexes and the level of cdk inhibitors to explain the inhibitory action of TGFbeta1 on cdk activity. Western blotting showed that the total level of the kinase inhibitor p21 (WAF1) increased after TGFbetal treatment. Our results indicate that a notably high level of p21(WAF1) was bound to cdk4/6 due to the treatment and that the binding of p21(WAF1) was associated with cyclin D-cdk4/6 complex decomposition.


CONCLUSIONS
Our investigation of the effect of TGFbetal on cell-cycle progression of a non-Hodgkin's lymphoma cell line of follicular lymphoma subtype showed that the TGFbeta1-induced growth arrest of malignant B cells was associated with the activation of CIP/KIP family members of cdk inhibitors.
Tvrdík
Daniel
D
Institute of Pathology, General Faculty Hospital, Prague, Czech Republic. daniel.tvrdikd@vfn.cz
D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D016393:Lymphoma, B-Cell / Q000378:metabolism*; D008224:Lymphoma, Follicular / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1
D018797:Cell Cycle Proteins; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1