Zhiping Zhang — Page 2

PubMed2002

Methoxychlor stimulates the mouse lactoferrin gene promoter through a GC-rich element.

The lactoferrin gene in the mouse uterus is a target gene for natural estrogens and xenoestrogens. One of the xenoestrogens is methyoxychlor, an insecticide that displays both estrogenic and antiandrogenic activities. Recently, methyoxychlor was found to stimulate lactoferrin gene expression in the uterus of an estrogen receptor null mouse. The present study is designed to uncover the methoxychlor response region in the mouse lactoferrin gene promoter. A series of different lengths of the mouse lactoferrin gene 5' flanking region were linked to a chloramphenicol acetyltransferase (CAT) reporter construct and transfected into human endometrial carcinoma HEC-1B cells, an estrogen receptor null cell line, in order to examine the methoxychlor response. The transfected cells were treated with methoxychlor or the metabolite of methoxychlor, HPTE, and the CAT reporter activities were measured. Constructs that contain a mouse lactoferrin 5' region longer than 100 bp were activated more than twofold by both methoxychlor and HPTE. The activation of the CAT reporter by the chemicals was dose dependent and reached saturation. Additional deletion mutants within the 100-bp region were tested, and a GC-rich sequence (GC-II) that we have previously characterized as an epidermal growth factor (EGF) response element was identified to be the region for the methoxychlor response. GC-II binds Sp1, Sp3, and IKLF transcription factors, collaborates with the AP1/CREB binding element, and confers the EGF response. Whether the effect of methoxychlor requires the AP1/CREB binding element has yet to be established; however, the present finding provides an alternative signaling pathway for the xenoestrogens.

Animals↗

PubMed2002

Cloning and characterization of the heart muscle isoform of sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) from crayfish.

This paper describes the cloning and functional characterization of the heart muscle isoform of Sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) from crayfish Procambarus clarkii. The complete crayfish heart SERCA, identified by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE), consists of 4495 bp with a 3060 bp open reading frame, coding for 1020 amino acids. This isoform differs from the previously identified axial abdominal (tail) muscle SERCA solely in its C-terminal amino acids. The last nine amino acids of the tail muscle isoform are replaced by 27 hydrophobic amino acids in the heart isoform that have the potential to form an additional transmembrane domain. Consistent with other invertebrate studies, Southern blot analysis suggested that the heart and tail muscle isoforms are encoded from the same gene that is equally related to SERCA-1, -2 and -3 of vertebrates. The tissue distributions of these two isoforms have been assessed using isoform-specific probes and northern analysis. A cardiac-specific probe bound only to a 5.8 kb species in heart and had minimal cross-hybridization with 7.6 and 5.8 kb species in eggs and no hybridization with tail muscle. A tail-isoform-specific probe hybridized with a 4.5 kb species in tail muscle and cross-hybridized with a 4.5 kb species in eggs and 8.8 kb in heart muscle. Both isoforms are expressed in eggs suggesting that transcripts are formed early in development and are subsequently broadly expressed in all tissue types. Expression of the cardiac muscle SERCA isoform varied with the stage of moulting. Expression was high in intermoult and decreased in premoult. However, expression was restored rapidly in postmoult (within 2 days) unlike expression of tail muscle SERCA, which remained downregulated for weeks. Differences in contractility between the two muscle types in the postmoult period may explain these expression patterns.

Amino Acid Sequence↗