The metalloproteinases degrade extracellular matrix (ECM) components and activate growth factors, thereby contributing to physiological events (tissue remodeling in pregnancy, wound healing, angiogenesis) and pathological conditions (cancer, arthritis, periodontitis). The intent of this review is to bring together various studies on transcriptional and post-transcriptional control of metalloproteinase expression. Certainly, much information is known as to the cis-elements and corresponding trans-activators regulating expression of these genes. We discuss the fact that a number of the metalloproteinase promoters share common structural features and, therefore, not surprisingly are co-regulated in their expression to some extent. More recently, much effort has been devoted to understanding the role of chromatin in regulating gene expression. While this area has been understudied with respect to matrix metalloproteinase (MMP) regulation, the literature indicates a convincing role for both histone modifications and chromatin-remodeling motors in controlling expression of multiple metalloproteinases. In addition to transcriptional control, mRNA stability and protein translation also contribute to the metalloproteinase product amount. We discuss such studies and how various biological cues, including TGF-b, regulate the levels of certain collagenases either solely through mRNA stabilization or by jointly targeting transcriptional and post-transcriptional mechanisms. We also discuss the current deficits in our knowledge, concerning tissue-specific expression and why despite elevated amounts/activity of trans-activators targeting MMP promoters in tumor cells, nevertheless, MMP expression is largely restricted to the stromal compartment. Finally, we argue for potential technologies to regulate MMP expression of utility in pathological conditions where these enzymes are aberrantly expressed.J cis-Elements and trans-Activators Regulating MMP Gene ExpressionAmple evidence indicates that MMP gene expression is, to a large extent, regulated at the transcriptional level. Indeed, the MMP promoters harbor several cis-elements allowing for the regulation of MMP gene expression by a diverse set of trans-activators including AP-1, PEA3, Sp-1, b-catenin/Tcf-4, and NF-kB (Fig. 1). Several of the MMP promoters are strikingly similar ( Fig. 1) and, in fact, share several cis-elements (Fig. 1), consistent with observations that some MMPs are co-regulated in their expression. In contrast, and somewhat surprisingly, the composition of the promoters of functionally related MMPs such as MMP-2/MMP-9 (gelatinase) or MMP-1/MMP-8 (collagenase) are distinct. Based on the composition of cis-elements, the MMP promoters can be roughly grouped into three categories (Fig. 1). The first group, including the majority of the MMP promoters, contains a TATA box at approximately À30 bp (relative to the transcription start site) and an AP-1-binding site at approximately À70 bp. Most of these promoters also contain an upstream PEA3-binding site that is ofte...
Activating transcription factor 3 (ATF3) is rapidly induced by diverse environmental insults including genotoxic stress. We report herein that its interaction with p53, enhanced by genotoxic stress, stabilizes the tumor suppressor thereby augmenting functions of the latter. Overexpression of ATF3 (but not a mutated ATF3 protein (D102-139) devoid of its p53-binding region) prevents p53 from MDM2-mediated degradation and leads to increased transcription from p53-regulated promoters. ATF3, but not the D102-139 protein, binds the p53 carboxy-terminus and diminishes its ubiquitination and nuclear export. Genotoxic-stressed ATF3-null mouse embryonic fibroblasts, or cells in which ATF3 was reduced by small interference RNA, show inefficient p53 induction and impaired apoptosis compared with wild-type cells. ATF3-null cells (but not wild-type cells), which poorly accumulate p53, are transformed by oncogenic Ras. Thus, ATF3 is a novel stress-activated regulator of p53 protein stability/ function providing the cell with a means of responding to a wide range of environmental insult, thus maintaining DNA integrity and protecting against cell transformation.
The 92-kDa type IV collagenase (92-kDa gelatinase B also referred to as MMP-9), which plays a critical role in extracellular matrix degradation, is regulated by growth factors that mediate their effects through the ras proto-oncogene. The current study was undertaken to determine the transcriptional requirements for the induction of 92-kDa gelatinase B expression by an activated ras oncogene. Transfection of OVCAR-3 cells with an expression vector encoding an activated Ha-ras increased 92-kDa gelatinolytic activity and stimulated (over 10-fold) the activity of a CAT reporter driven by 670 nucleotides of 5 flanking sequence of the 92-kDa gelatinase B gene. Transient assays using a CAT reporter driven by 5 deleted fragments of the 92-kDa gelatinase B promoter indicated that a region spanning ؊634 to ؊531 was required for optimal induction of the promoter. The individual deletion, or mutation, of a PEA3/ets (؊540) motif, AP-1 sites (؊533, ؊79), a NF-B (؊600) consensus sequence, and a GT box (؊52) substantially reduced the activation of the promoter by ras. An expression vector encoding the PEA3 transcription factor caused a 3-fold stimulation of the wild type but not the PEA3/ets-deleted 92-kDa gelatinase B promoter. Coexpression of a dominant negative c-jun antagonized the ras-dependent stimulation of the 92-kDa gelatinase B promoter-driven CAT reporter. The signaling pathway mediating the induction of 92-kDa gelatinase B promoter activity by ras was examined. The expression of a phosphatase (CL100) which inactivates multiple mitogen-activated protein kinase members abrogated the stimulation of 92-kDa gelatinase B promoter activity by ras. However, the expression of a kinase-deficient mitogen-activated protein kinase kinase 1 (MEK1) did not prevent the activation of the 92-kDa gelatinase B promoter by ras and a constitutively activated c-raf expression vector was insufficient for 92-kDa gelatinase B promoter activation. Thus, the stimulation of the 92-kDa gelatinase B promoter by ras requires multiple elements including closely spaced PEA3/ets and AP-1 sites and is MEK1-independent.The 92-kDa type IV matrix metalloproteinase (92-kDa gelatinase B also known as MMP-9) plays a major role in cell migration in both physiological and pathological processes (1-3) by facilitating the destruction of the type IV collagencontaining basement membrane which separates the epithelial and stromal compartments (4). The 92-kDa type IV collagenase is secreted as a proenzyme (5) and subsequently activated by multiple enzymes, including cathepsin G, trypsin, stromelysin 1 (6), and 72-kDa gelatinase A (7) by the removal of 73 amino acids from the amino terminus of the protease. The active enzyme, which is capable of digesting native type I, III, IV, and V collagens at nondenaturing temperatures (4, 6), consists of five domains: the aminoterminal and zinc-binding domains shared by all members of the metalloproteinase family, a collagen-binding fibronectinlike domain, a carboxyl-terminal hemopexin-like domain, and a unique 54-amino acid ...
Summary Autophagy constitutes a major cell protective mechanism eliminating damaged components and maintaining energy homoeostasis via recycling nutrients under normal/stressed conditions. Although the core components of autophagy have been well studied, regulation of autophagy at the transcriptional level is poorly understood. Herein, we establish ZKSCAN3, a zinc-finger family DNA-binding protein, as a transcriptional repressor of autophagy. Silencing of ZKSCAN3 induced autophagy and increased lysosome biogenesis. Importantly, we show that ZKSCAN3 represses transcription of a large gene set (>60) integral to, or regulatory for, autophagy and lysosome biogenesis/function and a subset of these genes, including Map1lC3b and Wipi2 represent direct targets. Interestingly, ZKSCAN3 and TFEB are oppositely regulated by starvation and in turn oppositely regulate lysosomal biogenesis and autophagy, suggesting that they act in conjunction. Altogether, our study uncovers an autophagy master-switch regulating the expression of a transcriptional network of genes integral to autophagy and lysosome biogenesis/function.
The function of the pro-apoptotic molecule BAD is regulated by phosphorylation of two sites, serine-112 (Ser-112) and . Phosphorylation at either site results in loss of the ability of BAD to heterodimerize with the survival proteins BCL-X L or BCL-2. Phosphorylated BAD binds to 14-3-3 and is sequestered in the cytoplasm. It has been shown that phosphorylation of BAD at Ser-136 is mediated by the serine/threonine protein kinase Akt-1/PKB which is downstream of phosphatidylinositol 3-kinase (PI3K). The signaling process leading to phosphorylation of BAD at Ser-112 has not been identi®ed. In this study, we show that phosphorylation of the two serine residues of BAD is di erentially regulated. While Ser-136 phosphorylation is concordant with activation of Akt, Ser-112 phosphorylation does not correlate with Akt activation. Instead, we demonstrate that activated Ras and Raf, which are upstream of mitogen-activated protein kinases (MAPK), stimulate selective phosphorylation of BAD at Ser-112. Furthermore, phosphorylation of Ser-112, but not Ser-136 requires activation of the MAPK pathway as the MEK inhibitor, PD 98059, blocks EGF-, as well as activated Ras-or Raf-mediated phosphorylation of BAD at Ser-112. Therefore, the PI3K-Akt and Ras-MAPK pathways converge at BAD by mediating phosphorylation of distinct serine residues.
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