Increased Electrophoretic Mobility of Long-Type GATA-6 Transcription Factor upon Substitution of Its PEST Sequence

The transcriptional factor GATA-6 gene produces two translational isoforms from a single mRNA through ribosomal leaky scanning. L-type GATA-6 has an extension of 146 amino acid residues at its amino terminus. In the extension, there is a unique PEST sequence (Glu31-Cys46), which is composed of an amino terminal Pro-rich segment and a carboxyl terminal Ser-cluster. Substitution of either half of the PEST sequence with Ala residues by cassette mutagenesis reduced the apparent molecular size of L-type GATA-6 on SDS-polyacrylamide gel-electrophoresis. However, the effect of substitution of the Pro-rich segment was much more significant;the mobility increase of the Pro-rich segment on the gel was 13% while that of the Ser-cluster was 8%. Substitution of each amino acid residue demonstrated that the effect of Pro substitution is greater than that of the Ser and Thr residues. Such increased mobility of L-type GATA-6 in the presence of a detergent may apparently correlate with the decrease in transcription activity in vivo as determined by means of luciferase reporter gene assay. The activity of ΔAla (with Ala residues instead of the PEST sequence) was reduced to one fifth of that of ΔA (with the PEST sequence). These results suggest that the PEST sequence of L-type GATA-6 does not function as a constitutive protein degradation signal, but rather plays structural and functional roles in the activation of gene expression on the GATA responsive promoter.

The Cytomegalovirus Enhancer Induces an Immediate Response to the Myosin Light Chain 2v Promoter during P19CL6 Cell Differentiation

The P19CL6 mouse embryonic carcinoma cells efficiently differentiate into cardiac muscle cells in the presence of DMSO. A reporter plasmid for cardiac muscle differentiation was constructed by connecting the CMV enhancer and a 250 bp MLC-2v promoter in front of the GFP gene to further evaluate the role of the CMV enhancer. This plasmid (pCBVenh/MLC-2vpro/EGFP) was stably introduced into P19CL6 cells, and the transfectant differentiated into cardiomyocytes with DMSO. Upon DMSO addition, GFP was immediately transcribed (within 2 days) and the amount of the transcript increased with cultivation. Concomitantly, GFP fluorescence was detected in the cells under a microscope. However, native MLC-2v was transcribed later on day 4. This expression time course is different from that of GFP. Clearly the CMV enhancer responded immediately to DMSO. Since GATA DNA-binding proteins play crucial roles in the initiation of cardiomyocyte differentiation, such a response could be ascribed to the presence of multiple GATA motifs in the enhancer sequence but not in the native MLC-2v promoter. Thus the CMV enhancer may be not only useful for gene therapy and monitoring cell differentiation but also the study of the role of GATA transcription factors expressed in P19CL6 cells.

Role of the PEST sequence in the long-type GATA-6 DNA-binding protein expressed in human cancer cell lines

GATA-6 mRNA utilizes two Met-codons in frame as translational initiation codons in cultured mammalian cells. Deletion of the nucleotide sequence encoding the PEST sequence between the two initiation codons unusually reduced the protein molecular size on SDS-polyacrylamide gel-electrophoresis. The reduced molecular size is ascribed to the molecular property of GATA-6, since both amino-and carboxy-lterminal tags introduced into GATA-6 were detected on the gel. This PEST sequence seems to contribute to expansion of the long-type GATA-6 molecule. The long-type GATA-6 containing the PEST sequence exhibits more activation potential than that without this sequence, the latter’s activity being similar to that of the short-type GATA-6. We further demonstrated that human colon and lung cancer cell lines express both the long-type GATA-6 and the short-type GATA-6 in their nuclei.

Recombinant Human REG I<i>α</i>Aggregates <i>Staphylococcus aureus</i>—Exhibits a Lectin-Like Function

Staphylococcus aureus is pathogenic to humans with worldwide health care concern due to its ability to evade the immune system and develop resistance to multiple drugs. Reg family proteins are C-type lectins with antimicrobial properties. Bacterial aggregation through binding to microbial cell surface sugar and/or lipid moieties is key mechanism employed in the process. In the present study we have analysed the antimicrobial effect of human REG Iα on S. aureus. Aggregation of mid-log phase culture of S. aureus was observed in presence of purified recombinant REG Iα. Therefore REG Iα can be applied in eliminating S. aureus infections in humans.