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W Scheper

Publications and source records attributed to W Scheper.

9 recordsLinked to original sources
PubMed1996

Growth-condition-dependent regulation of insulin-like growth factor II mRNA stability.

Insulin-like growth factor II (IGF-II) is synthesized in many tissues, but the main site of production is the liver. In this paper we show that IGF-II mRNA levels are dependent on the growth conditions of the cells. In Hep3B cells, serum deprivation leads to a marked increase in IGF-II mRNA levels. Serum stimulation of starved Hep3B cells induces a decrease in the amount of IGF-II mRNA, which is not caused by a change in promoter activity. IGF-II mRNAs are subject to endonucleolytic cleavage, a process that requires two widely separated elements in the 3' untranslated region of the mRNA. Specific regions of these elements can form a stable stem structure which is involved in the formation of RNA-protein complexes. By employing electrophoretic mobility shift assays, two complexes have been identified in cytoplasmic extracts of Hep3B cells. The formation of these complexes is related to the growth conditions of the cells and is correlated with the regulation of IGF-II mRNA levels. Our data suggest that, depending on whether serum is present or absent, a transition from one complex to the other occurs. A decrease in the IGF-II mRNA level is also observed when IGF-I or IGF-II is added to serum-deprived Hep3B cells, possibly providing a feedback mechanism for IGF-II production. The serum-induced degradation of IGF-II mRNAs does not require de novo protein synthesis, and is abolished by rapamycin, an inhibitor of p70 S6 kinase.

Base Sequence↗
PubMed1996

The cis-acting elements involved in endonucleolytic cleavage of the 3' UTR of human IGF-II mRNAs bind a 50 kDa protein.

Site-specific cleavage of human insulin-like growth factor II mRNAs requires two cis-acting elements, I and II, that are both located in the 3' untranslated region and separated by almost 2 kb. These elements can interact and form a stable RNA-RNA stem structure. In this study we have initiated the investigation of transacting factors involved in the cleavage of IGF-II mRNAs. The products of the cleavage reaction accumulate in the cytoplasm, suggesting that cleavage occurs in this cellular compartment. By electrophoretic mobility shift assays, we have identified a cytoplasmic protein with an apparent molecular weight of 48-50 kDa, IGF-II cleavage unit binding protein (ICU-BP), that binds to the stem structure formed by interaction of parts of the cis-acting elements I and II. The binding is resistant to high K+ concentrations and is dependent on Mg2+. In addition, ICU-BP binding is dependent on the cell density and correlates inversely with the IGM-II mRNA levels. In vivo cross-linking data show that this protein is associated with IGF-II mRNAs in vivo.

Base Sequence↗
PubMed1995

Long-range RNA interaction of two sequence elements required for endonucleolytic cleavage of human insulin-like growth factor II mRNAs.

Human insulin-like growth factor II (IGF-II) mRNAs are subject to site-specific endonucleolytic cleavage in the 3' untranslated region, leading to an unstable 5' cleavage product containing the IGF-II coding region and a very stable 3' cleavage product of 1.8 kb. This endonucleolytic cleavage is most probably the first and rate-limiting step in degradation of IGF-II mRNAs. Two sequence elements within the 3' untranslated region are required for cleavage: element I, located approximately 2 kb upstream of the cleavage site, and element II, encompassing the cleavage site itself. We have identified a stable double-stranded RNA stem structure (delta G = -100 kcal/mol [418.4 kJ/mol]) that can be formed between element I and a region downstream of the cleavage site in element II. This structure is conserved among human, rat, and mouse mRNAs. Detailed analysis of the requirements for cleavage shows that the relative position of the elements is not essential for cleavage. Furthermore, the distance between the coding region and the cleavage site does not affect the cleavage reaction. Mutational analysis of the long-range RNA-RNA interaction shows that not only the double-stranded character but also the sequence of the stable RNA stem is important for cleavage.

Animals↗
PubMed1993

Transcriptional and post-transcriptional regulation of the human IGF-II gene expression.

The human insulin-like growth factor II (IGF-II) gene consists of nine exons and has four promoters (P1-4). The promoters exhibit a tissue-specific and developmental stage-dependent expression pattern. In fetal liver promoters P2-4 are expressed, but after birth these promoters are shut off and another promoter, P1, is activated. We have investigated some properties of the human promoters P1 and P3 and identified a number of sequence elements, that are recognized by transcription factors. Promoter P1 is stimulated by the liver-enriched transcription factors C/EBP and LAP, whereas in the proximal region of P3 we have identified several elements that are recognized by transcription factors, including krox20/egr2 and krox24/erg1. Besides transcriptional regulation of expression also regulation at the post-transcriptional level occurs. We have found that the IGF-II mRNAs are subjected to site-specific endonucleolytic cleavage yielding a labile 5' specific fragment and a stable polyadenylated 3' specific cleavage product of 1.8 kb. Two widely separated sequence elements within the last exon were identified that are able to interact and yield a double-stranded stem structure. It is likely that this structure is essential for post-transcriptional cleavage of IGF-II mRNAs.

Animals↗
PubMed1992

Site-specific cleavage of IGF-II mRNAs requires sequence elements from two distinct regions of the IGF-II gene.

The human insulin-like growth factor II (IGF-II) gene constitutes a complex transcriptional unit that contains nine exons and four promoters. Expression of the IGF-II gene yields a family of mRNAs that all encode prepro-IGF-II. In addition, a stable 1.8 kb RNA is formed that is derived from the 3' untranslated region of exon 9. Recently, we have shown that this RNA species arises by site-specific endonucleolytic cleavage of IGF-II mRNAs and not by transcription from a separate promoter. In the present study we establish that two widely separated sequence elements of approximately 300 nucleotides, both located within exon 9, are required for this cleavage reaction. The first element encompasses about 200 nucleotides upstream and 100 nucleotides downstream of the cleavage site, while the second element is located within a region of 330 nucleotides about 2 kb upstream of the cleavage site. Interestingly, site-specific cleavage also occurred when a fragment from exon 9 of the IGF-II gene containing these two elements was inserted into the 3' untranslated part of the beta-globin gene. Apparently, the expressed hybrid beta-globin-IGF-II mRNA contains all the regulatory elements to confer site-specific endonucleolytic cleavage.

Alternative Splicing↗
PubMed1978

[Fixing the time and date of photograph (author's transl)].

A system is described to obtain on photographs and slides an automatic printout of patient number, eye and time. The time is recorded in minutes, seconds and tenth of seconds or in minutes and seconds. The time-recording can be switched off if only patient and eye identification is needed.

Documentation↗
PubMed1977

Vertical motor fusion.

An analysis is given of the eye movements which take place in vertical fusion. These movements are compared with the movements that occur in horizontal fusion. The differences and similarities that can lead to a model are stressed.

Eye Movements↗