S I Hasegawa | PubMed Health

PubMed2001

Proprotein convertase PACE4 is down-regulated by the basic helix-loop-helix transcription factor hASH-1 and MASH-1.

PACE4 is a mammalian subtilisin-like proprotein convertase that activates transforming growth factor (TGF)-beta-related proteins such as bone morphogenetic protein 2 (BMP2), BMP4 and Nodal and exhibits a dynamic expression pattern during embryogenesis. We recently determined that the 1 kb 5'-upstream region of the PACE4 gene contains 12 E-box (E1-E12) elements and that an E-box cluster (E4-E9) acts as a negative regulator [Tsuji, Yoshida, Hasegawa, Bando, Yoshida, Koide, Mori and Matsuda (1999) J. Biochem. (Tokyo) 126, 494-502]. It is known that the mammalian achaete-scute homologue 1 (MASH-1) binds specifically to an E-box (CACCTG) sequence in collaboration with E47, a ubiquitously expressed basic helix-loop-helix (bHLH) factor. To identify the roles of the bHLH factor and E-box elements in regulating PACE4 gene expression in neural development, we analysed the effects of human achaete-scute homologue 1 (hASH-1) on PACE4 gene expression with various neuroblastoma cell lines. The expressions of PACE4 and hASH-1 are correlated inversely in these cell lines. The overexpression of hASH-1 or MASH-1 causes a marked decrease in endogenous PACE4 gene expression but has no effect on the expression of other subtilisin-like proprotein convertases such as furin, PC5/6 and PC7/8. In contrast, other neural bHLH factors (MATH-1, MATH-2, neurogenin 1, neurogenin 2, neurogenin 3 and E47) did not affect PACE4 gene expression. Furthermore, an E-box cluster was a negative regulatory element for the promoter activity in NBL-S cells expressing hASH-1 at high level as determined by a luciferase assay. Binding of hASH-1 to the E-box cluster was confirmed by gel mobility-shift assay. In the present study we identified the PACE4 gene as one of the targets of hASH-1, which is a key factor in the initiation of neural differentiation. These results suggest that the alteration of PACE4 gene expression by hASH-1 causes rapid changes in the biological activities of TGF-beta-related proteins via post-translational modification of these proteins.

Basic Helix-Loop-Helix Proteins↗

PubMed1977

Biochemical characterization of the neuron. ATPase and acetylcholinesterase activities of neuronal cell bodies isolated in bulk from the pig brain stem.

Nerve cell bodies, large and multipolar, were isolated in bulk with the least possible contamination from the pig brain stem. The activities of two neurobiologically important membrane enzymes, Na+, K+-ATPase, and acetylcholinesterase, in the isolated cell bodies were estimated. Na+, K+-ATPase [EC 3.6.1.4], more accurately called ouabain-sensitive ATPase of the nerve cell body, hydrolyzed 94 micronmoles of ATP per h per 100 mg of protein. This activity was one-fourth that in the brain stem. Nerve cell bodies contained a large amount of Ca2+, 275 micronmoles per 100 mg of protein, about half of which was calculated to exist as compounds other than calcium orthophosphate. However, the Na+, K+-ATPase of the nerve cell bodies was not stimulated by EGTA, in contrast to that of the brain stem. Acetylcholinesterase [EC 3.1.1.7] and cholinesterase [EC 3.1.1.8] activities were estimated separately by the use of the specific inhibitors Persidol and BW 284C51 dibromide. Acetylcholinesterase was almost completely responsible for the hydrolysis of acetylcholine in the nerve cell bodies isolated from the brain stem and little cholinesterase activity was detected. 1300-1400 micronmoles of acetylcholine was hydrolyzed per h per 100 mg of protein of the neuronal cell bodies; this activity was about four times higher than that in the brain stem. The differences between the specific activities of Na+, K+-ATPase, and acetylcholinesterase in theneuronal cell bodies and the brain stem are discussed in the light of electron microscopic analysis of the distribution of these enzymes and the preservation of the plasma membrane of the isolated cell bodies.

Acetylcholinesterase↗