The Repressor Element 1-Silencing Transcription factor (REST) is a negative regulator of genes implicated in variety of diseases including human neointimal hyperplasia (Ooi and Wood, 2007). We have previously reported its role in controlling pro-proliferative genes in vascular smooth muscle and downregulation of REST expression is important for smooth muscle proliferation (Cheong et al, 2005). However the mechanisms regulating REST levels remain unknown. Human saphenous vein smooth muscle cells (VSMC) were grown from discarded human saphenous veins obtained at coronary artery bypass graft surgery with ethical consent. Data are presented as means ± sem and were statistically analysed by 1-way ANOVA. Statistical significance was defined as a value of P<0.05. We observe that PDGF, a growth factor associated with atherosclerosis and restenosis, significantly inhibited the REST promoter-driven luciferase activity in VSMC by 43.2±11.1% (n=6). Using quantitative RT-PCR, we show that PDGF treatment resulted in a reduction of REST mRNA expression 34.1±7% (n=20-26). Activation of the PDGF receptor initiates MAPK/MEK, PKC, PI3K and calcium-calmodulin signalling (Hughes et al, 1996). Pretreatment with W-7 (a calmodulin antagonist) significantly prevented REST mRNA downregulation by PDGF, suggesting a role for the calcium-calmodulin pathway. Preincubation with KN-62 (a calcium-calmodulin dependent kinase II (CAMKII) inhibitor) attenuated the effect of PDGF on REST mRNA expression. Likewise, KN-93 (another CAMKII inhibitor) but not its control analog KN-92 was effective in preventing REST mRNA downregulation. Pretreatment of VSMC with siRNA against the δ-isoform of CAMKII also significantly prevented PDGF-induced REST mRNA downregulation. Neither PD98059 (a MEK-1 specific inhibitor), calphostin (a PKC specific inhibitor) nor wortmannin (a PI3K specific inhibitor) had an effect on PDGF-induced REST downregulation. We here identify a PDGF-calmodulin dependent kinase pathway that regulates REST mRNA levels in vascular smooth muscle cells. This is the first pathway to be identified that impacts upon REST expression and marks an important step in understanding the molecular mechanisms controlling vascular smooth muscle proliferation.