Cyclin A down-regulation in TGFβ1-arrested follicular lymphoma cells

Transforming growth factor beta1 (TGF beta1) induces growth arrest in many cell types, including B lymphocytes. We examined the effect of TGF on cell cycle progression of a non-Hodgkin lymphoma cell line of follicular lymphoma subtype (FL). After 48 h of TGF beta1 (10 ng/ml) treatment, a significantly increased number of DoHH2 cells was retained in G(0)/G(1) phase. We examined the level of cell cycle components, cyclins, cyclin-dependent kinases (cdk), and their inhibitors. We found that the expression of cyclin A and p21(WAF1) molecules was primarily modulated by TGF beta1 treatment while the expression of other regulatory components, like cyclins D, cyclin E, cdk2, cdk4, and cdk6 or p15(INK4B), p16(INK4A), and p27(KIP1) was not significantly affected. We further examined expression and activity of CREB/ATF family members to examine their roles in cyclin A inhibition. The binding activity of CREB-1 and ATF-8 to the CRE region of the cyclin A promoter was almost completely abolished due to the treatment. The total level of CREB-1, ATF-2, and ATF-3 was notably reduced. Moreover, CREB-1 was dephosphorylated due to the treatment as revealed by immunoblotting. We assume that down-regulation of cyclin A was mediated by the absence of CREB/ATF activation dimers. The profound effect on the ATF family of transcription factors indicates the complexity of TGF beta1 action on FL B malignant cells. (C) 2000 Academic Press.