The adenomatous polyposis coli (APC) tumor suppressor protein binds to beta-catenin, a protein recently shown to interact with Tcf and Lef transcription factors. The gene encoding hTcf-4, a Tcf family member that is expressed in colonic epithelium, was cloned and characterized. hTcf-4 transactivates transcription only when associated with beta-catenin. Nuclei of APC-/- colon carcinoma cells were found to contain a stable beta-catenin-hTcf-4 complex that was constitutively active, as measured by transcription of a Tcf reporter gene. Reintroduction of APC removed beta-catenin from hTcf-4 and abrogated the transcriptional transactivation. Constitutive transcription of Tcf target genes, caused by loss of APC function, may be a crucial event in the early transformation of colonic epithelium.

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There is substantial interest in applying proteomics to obtain better understanding of disease processes and to develop new biomarkers for diagnosis and early detection of cardiovascular diseases. 5,6 The purpose of the present study was to investigate proteomic changes in reverse remodeling during LVAD support. Because the degree of reverse remodeling is more pronounced in patients with nonischemic dilated cardiomyopathy (DCM), 7 we focused on this subset of patients. Recently, we found that levels of α-1-antichymotrypsin (ACT) expression decrease in myocardial tissue during pulsatile-LVAD support, which was detected by proteomics and confirmed by immunosorbent assays. 8 However, the molecular pathways regulating ACT expression in the heart were not explored.Clinically, pulsatile-LVAD support is being replaced by continuous-flow LVAD (cf-LVAD) support. Therefore, we performed proteomics in plasma and heart tissue of DCM Correspondence to Sjoukje Irene Lok, MD, University Medical Center Utrecht, Department of Cardiology, Huispostnummer H04.312, Postbus 85500, 3508 GA Utrecht, The Netherlands. E-mail s.lok@umcutrecht.nl Background-Better understanding of the molecular mechanisms of remodeling has become a major objective of heart failure (HF) research to stop or reverse its progression. Left ventricular assist devices (LVADs) are being used in patients with HF, leading to partial reverse remodeling. In the present study, proteomics identified significant changes in α-1-antichymotrypsin (ACT) levels during LVAD support. Moreover, the potential role of ACT in reverse remodeling was studied in detail. Methods and Results-Expression of ACT mRNA (quantitative-polymerase chain reaction) decreased significantly in post-LVAD myocardial tissue compared with pre-LVAD tissue (n=15; P<0.01). Immunohistochemistry revealed that ACT expression and localization changed during LVAD support. Circulating ACT levels were elevated in HF patients (n=18) as compared with healthy controls (n=6; P=0.001) and normalized by 6 months of LVAD support. Because increasing evidence implicates that microRNAs (miRs) are involved in myocardial disease processes, we also investigated whether ACT is post-transcriptionally regulated by miRs. Bioinformatics analysis pointed miR-137 as a potential regulator of ACT. The miR-137 expression is inversely correlated with ACT mRNA in myocardial tissue. Luciferase activity assays confirmed ACT as a direct target for miR-137, and in situ hybridization indicated that ACT and miR-137 were mainly localized in cardiomyocytes and stromal cells. Conclusions-High ACT plasma levels in HF normalized during LVAD support, which coincides with decreased ACT mRNA in heart tissue, whereas miR-137 levels increased. MiR-137 directly targeted ACT, thereby indicating that ACT and miR-137 play a role in the pathophysiology of HF and reverse remodeling during mechanical support. Delineating the role of miRs in post-transcriptional gene regulation offers new insight into the mechanisms by which the heart adapts to mechanical suppo...