No abstract

The Ets1 proto-oncoprotein is a member of the Ets family of transcription factors that share a unique DNA binding domain, the Ets domain. The DNA binding activity of Ets1 is controlled by kinases and transcription factors. Some transcription factors, such as AML-1, regulate Ets1 by targeting its autoinhibitory module. Others, such as Pax-5, alter Ets1 DNA binding properties. Ets1 harbors two phosphorylation sites, threonine-38 and an array of serines within the exon VII domain. Phosphorylation of threonine-38 by ERK1/2 activates Ets1, whereas phosphorylation of the exon VII domain by CaMKII or MLCK inhibits Ets1 DNA binding activity. Ets1 is expressed by numerous cell types. In haemotopoietic cells, it contributes to the regulation of cellular differentiation. In a variety of other cells, including endothelial cells, vascular smooth muscle cells and epithelial cancer cells, Ets1 promotes invasive behavior. Regulation of MMP1, MMP3, MMP9 and uPA as well as of VEGF and VEGF receptor gene expression has been ascribed to Ets1. In tumors, Ets1 expression is indicative of poorer prognosis.

Beta-actin is often used as a loading control in Western blot analysis. We analyzed the ability of beta-actin-specific antibodies to recognize differences in protein loading. We found that, at higher total protein loads as required for the detection of low-abundance proteins, beta-actin-specific antibodies failed to distinguish differences in actin protein levels. Diluting the antibody working solution or changing the incubation time had little effect on this phenomenon. This shows that beta-Actin is not a reliable loading control in Western blot analysis. In general, it appeared that, at longer incubation times, antibodies seem to be less able to pick up differences in the level of its target protein.

No abstract

The majority of breast cancers metastasizing to bone secrete parathyroid hormone-related protein (PTHrP). PTHrP induces local osteolysis that leads to activation of bone matrix-borne transforming growth factor ␤ (TGF␤). In turn, TGF␤ stimulates PTHrP expression and, thereby, accelerates bone destruction. We studied the mechanism by which TGF␤ activates PTHrP in invasive MDA-MB-231 breast cancer cells. We demonstrate that TGF␤1 up-regulates specifically the level of PTHrP P3 promoter-derived RNA in an actinomycin D-sensitive fashion. Transient transfection studies revealed that TGF␤1 and its effector Smad3 are able to activate the P3 promoter. This effect depended upon an AGAC box and a previously described Ets binding site. Addition of Ets1 greatly enhanced the Smad3/TGF␤-mediated activation. Ets2 had also some effect, whereas other Ets proteins, Elf-1, Ese-1, and Erf-1, failed to cooperate with Smad3. In comparison, Ets1 did not increase Smad3/TGF␤-induced stimulation of the TGF␤-responsive plasminogen activator inhibitor 1 (PAI-1) promoter. Smad3 and Smad4 were able to specifically interact with the PTHrP P3-AGAC box and to bind to the P3 promoter together with Ets1. Inhibition of endogenous Ets1 expression by calphostin C abrogated TGF␤-induced up-regulation of the P3 transcript, whereas it did not affect the TGF␤ effect on PAI expression. In TGF␤ receptor II-and Ets1-deficient, noninvasive MCF-7 breast cancer cells, TGF␤1 neither influenced endogenous PTHrP expression nor stimulated the PTHrP P3 promoter. These data suggest that TGF␤ activates PTHrP expression by specifically up-regulating transcription from the PTHrP P3 promoter through a novel Smad3/Ets1 synergism.Parathyroid hormone-related protein (PTHrP)