Functional and biological properties of the nuclear receptor coregulator PELP1/MNAR

Proline-, glutamic acid-, and leucine-rich protein (PELP)1, also known as modulator of nongenomic actions of the estrogen receptor (MNAR), is a novel nuclear receptor coregulator with a multitude of functions. PELP1/MNAR serves as a scaffolding protein that couples various signaling complexes with nuclear receptors and participates in genomic and nongenomic functions. Recent data suggest that PELP1/MNAR expression is deregulated in several cancers, including breast, endometrial, prostate, and ovarian cancer, and that PELP1/MNAR interacts with several oncogenes. In this review, we summarize the emerging biological properties and functions of PELP1/MNAR

Heregulin induces expression, DNA binding activity and transactivating functions of basic leucine zipper activating transcription factor 4

Heregulin β1 (HRG), a combinatorial ligand for human epidermal growth factor receptor 3 and human epidermal growth factor receptor 4 receptors, is a regulatory secretory polypeptide with distinct biological effects such as growth stimulation, differentiation, invasiveness and migration in breast cancer cells. The mechanism underlying the diverse functions of HRG is not well established, but it is believed to be dependent on the induced changes in expression of specific cellular gene products, their modification, or both. The binding of basic leucine zipper transcription factors to the cAMP response element is known to activate a variety of gene products with a role or roles in growth regulation. In the studies presented here, we identified basic leucine zipper Activating Transcription Factor (ATF) 4 as one of the HRG-inducible gene product. We demonstrated that HRG stimulation of human cancer cells induces expression of ATF4 mRNA and protein, ATF4 DNA binding activity and ATF4 transactivating function. Consistent with its role as a transcriptional activator, HRG-stimulated ATF4 protein stimulated the transcription from an artificial promoter with three tandem ATF sites or from a naturally occurring promoter with ATF4 sites such as E-selectin. We also demonstrated a preferential role of the HRG-stimulated mitogen-activated protein kinase pathway, but not the phosphatidylinositol 3′-kinase pathway, in supporting the observed increase in ATF4 DNA binding activity and transcription from E-selectin promoter in HRG-stimulated cells. Because ATF4 binding sites are present in a variety of growth-regulating cellular genes, these findings suggest that the stimulation of ATF4 expression and its transactivating functions may constitute an important mechanism of HRG-mediated regulation of putative genes with diversified functions. The present study is the first demonstration of regulation of expression and transactivation ability of ATF4 by any polypeptide growth factor

Regulation of microfilament reorganization and invasiveness of breast cancer cells by kinase dead p21-activated kinase-1

Stimulation of growth factor signaling has been implicated in the development of invasive phenotype and p21-activated kinase (PAK1) activation in human breast epithelial cancer cells. To further explore the roles of PAK1 in the invasive behavior of breast cancer cells, in the present study we investigated the influence of inhibition of PAK1 activity on the reorganization of cytoskeleton components that control motility and invasiveness of cells, using a highly invasive breast cancer MDA-MB435 as a model system. Our results demonstrate that overexpression of a kinase dead K299R PAK1 mutant leads to suppression of motile phenotypes as well as invasiveness of cells both in the absence or presence of exogenous heregulin-β1. In addition, these phenotypic changes were accompanied by a blockade of disassembly of focal adhesion points, stabilization of stress fibers, and enhanced cell spreading and were dependent on the presence of the kinase dead domain but independent of the presence of the Rac/cdc42 intact (Cdc42/Rac interactive binding) domain of PAK1. We also demonstrated that in K299R PAK1-expressing cells, F-actin filaments were stabilized by persistent co-localization with the actin-binding proteins tropomyosin and caldesmon. Extension of these studies to invasive breast cancer MDA-MB231 cells illustrated that conditional expression of kinase-defective K299R PAK1 was also accompanied by persistent cell spreading, multiple focal adhesion points, and reduced invasiveness. Furthermore, inhibition of PAK1 activity in breast cancer cells was associated with a reduction in c-Jun N-terminal kinase activity, inhibition of DNA binding activity of transcription factor AP-1, and suppression of in vivo transcription driven by AP-1 promoter (known to be involved in breast cancer invasion). These findings suggest that PAK1 downstream pathways have a role in the development and maintenance of invasive phenotypes in breast cancer cells

Regulation of cyclooxygenase-2 pathway by HER2 receptor

Emerging lines of evidence suggest that in addition to growth factors, the process of colorectal tumorigenesis may also be driven by the upregulation of the inducible form of cyclooxygenase-2 (COX-2), an enzyme responsible for the conversion of arachidonic acid to PGEs. The present study was undertaken to investigate the expression and activation of the HER family members, and to explore the regulation of COX-2 expression by the HER2 pathway in human colorectal cancer cells. Here, we report that human colorectal cancer cell lines express abundant levels of HER2 and HER3 receptors, and are growth-stimulated by recombinant neu-differentiation factor-beta 1 (NDF). NDF-treatment of colorectal cancer cells was accompanied by increased tyrosine phosphorylation and heterodimerization of HER3 with HER2. In addition, we demonstrated that HER2 and HER3 receptors in colorectal cancer cells are constitutively phosphorylated on tyrosine residues and form heterodimeric complexes in the absence of exogenous NDF. Inhibition of HER2/HER3 signaling by an anti-HER3 mAb against the ligand binding site resulted in a decrease in the levels of constitutively activated HER2/HER3 heterodimers, and the unexpected reduction of COX-2 expression. Activation of the HER2/HER3 pathway by NDF induced the activation of COX-2 promoter, expression of COX-2 mRNA, COX-2 protein and accumulation of prostaglandin E2 in the culture medium. Finally, we demonstrated that NDF promotes the ability of colorectal cancer cells to survive in an extracellular matrix milieu, such as Matrigel, and also to invade through a 8 μm porous membrane. These biological activities of NDF and its stimulation of cell proliferation are blocked by a specific inhibitor of COX-2. Taken together, our findings provide the first biochemical evidence of a possible role of the COX-2 pathway in the mitogenic action of NDF in colorectal cancer cells where it may be constitutively upregulated due to the autocrine/paracrine activation of HER2/HER3 heterodimers

Heregulin and HER2 signaling selectively activates c-Src phosphorylation at tyrosine 215

AbstractTo elucidate the molecular mechanisms by which human epidermal growth factor receptor/heregulin (HER2/HRG) influence the migratory potential of breast cancer cells, we have used phospho-specific antibodies against c-Src kinase and focal adhesion kinase (FAK). This study establishes that HER2/HRG signaling selectively upregulates Tyr phosphorylation of c-Src at Tyr-215 located within the SH2 domain, increases c-Src kinase activity and selectively upregulates Tyr phosphorylation of FAK at Tyr-861. HER2-overexpressing tumors showed increased levels of c-Src phosphorylation at Tyr-215. These findings suggest that HER2/HRG influence metastasis of breast cancer cells through a novel signaling pathway involving phosphorylation of FAK tyrosine 861 via activation of c-Src tyrosine 215

The Clinical Aspects of Saroglitazar and its Side Effects

The new substance element has been known as novel antidiabetic drug, eg: saroglitazar. saroglitazar is a medication used to treat type-2 diabetes. saroglitazar was known under the exchange name Lipaglyn, created by Zydus cadila. lipaglyn is the first drug approved to treat type-2diabetes mellitus by the drug controller general of India in june 2013. Lipaglyn is demonstrated for the patients experiencing diabetes dyslipidaemia. It is given once daily for treatment. Saroglitazar manages the lipid parameters just as glycemic control. [1] Keywords: Anti-diabetic, dual PPAR agonist, glitazar, hypertriglyceridemia, insulin sensitizer, Lipaglyn, AE’s (adverse effects)

Regulation of rDNA Transcription by Proto-Oncogene PELP1

Proline-, glutamic acid-, and leucine-rich protein (PELP1) is a novel nuclear receptor coregulator with a multitude of functions. PELP1 serves as a scaffolding protein that couples various signaling complexes with nuclear receptors and participates as a transcriptional coregulator. Recent data suggest that PELP1 expression is deregulated in hormonal cancers, and that PELP1 functions as a proto-oncogene; however, the mechanism by which PELP1 promotes oncogenesis remains elusive.Using pharmacological inhibitors, confocal microscopy and biochemical assays, we demonstrated that PELP1 is localized in the nucleolus and that PELP1 is associated with the active ribosomal RNA transcription. Cell synchronization studies showed that PELP1 nucleolar localization varies and the greatest amount of nucleolar localization was observed during S and G2 phases. Using pharmacological compounds and CDK site mutants of PELP1, we found that CDK's activity plays an important role on PELP1 nucleolar localization. Depletion of PELP1 by siRNA decreased the expression of pre-rRNA. Reporter gene assays using ribosomal DNA (pHrD) luc-reporter revealed that PELP1WT but not PELP1MT enhanced the expression of reporter. Deletion of nucleolar domains abolished PELP1-mediated activation of the pHrD reporter. ChIP analysis revealed that PELP1 is recruited to the promoter regions of rDNA and is needed for optimal transcription of ribosomal RNA.Collectively, our results suggest that proto-oncogene PELP1 plays a vital role in rDNA transcription. PELP1 modulation of rRNA transcription, a key step in ribosomal biogenesis may have implications in PELP1-mediated oncogenic functions

Essential functions of p21-activated kinase 1 in morphogenesis and differentiation of mammary glands

Although growth factors have been shown to influence mammary gland development, the nature of downstream effectors remains elusive. In this study, we show that the expression of p21-activated kinase (Pak)1, a serine/threonine protein kinase, is activated in mammary glands during pregnancy and lactation. By targeting an ectopic expression of a kinase-dead Pak1 mutant under the control of ovine β-lactoglobulin promoter, we found that the mammary glands of female mice expressing kinase-dead Pak1 transgene revealed incomplete lobuloalveolar development and impaired functional differentiation. The expression of whey acidic protein and β-casein and the amount of activated Stat5 in the nuclei of epithelial cells in transgenic mice were drastically reduced. Further analysis of the underlying mechanisms revealed that Pak1 stimulated β-casein promoter activity in normal mouse mammary epithelial cells and also cooperated with Stat5a. Pak1 directly interacted with and phosphorylated Stat5a at Ser 779, and both COOH-terminal deletion containing Ser 779 of Stat5a and the Ser 779 to Ala mutation completely prevented the ability of Pak1 to stimulate β-casein promoter. Mammary glands expressing inactive Pak1 exhibited a reduction of Stat5a Ser 779 phosphorylation. These findings suggest that Pak1 is required for alveolar morphogenesis and lactation function, and thus, identify novel functions of Pak1 in the mammary gland development

Growth factors regulate heterogeneous nuclear ribonucleoprotein K expression and function

Epidermal Growth Factor (EGF) family of growth factors and their receptors regulate normal and cancerous epithelial cell proliferation, a process that can be suppressed by antireceptor blocking antibodies. To identify genes whose expression may be modulated by antireceptor blocking antibodies, we performed a differential display screen with cells grown in the presence or absence of antireceptor blocking antibodies; isolates from one cDNA clone were 100% identical to human heterogeneous nuclear ribonucleoprotein K (hnRNP K), a protein with a conserved KH motif and RGG boxes, has been implicated in such functions as sequence-specific DNA binding, transcription, RNA binding and nucleocytoplasmic shuttling. Both EGF and heregulin-β1 induced expression of hnRNP K mRNA and protein in human breast cancer cells. This growth factor-mediated hnRNP K expression was effectively blocked by pretreatment of cultures with humanized anti-EGF Receptor (EGFR) antibody C225, or anti-human epidermal growth factor receptor-2 (HER2) antibody. Anti-EGFR monoclonal antibody also caused regression of human tumor xenografts and reduction in hnRNP K levels in athymic mice. Samples from grade III human breast cancer contained more hnRNP K protein than samples from grade II cancer. Finally, overexpression of hnRNP K in breast cancer cells significantly increased target c-myc promoter activity and c-Myc protein, hnRNP K protein levels, and enhanced breast cancer cell proliferation and growth in an anchorage-independent manner. These results suggested that the activity of human EGF receptor family members regulates hnRNP K expression by extracellular growth promoting signals and that therapeutic humanized antibodies against EGFR and HER2 can effectively block this function