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M Birrer

Publications and source records attributed to M Birrer.

28 records · Page 2Linked to original sources
PubMed1995

Bombesin stimulates c-fos and c-jun mRNAs in small cell lung cancer cells.

The effects of bombesin/gastrin-releasing peptide (BN/GRP) on c-fos and c-jun gene expression were investigated using small cell lung cancer (SCLC) cells. BN (10 nM) increased c-fos mRNA fivefold using NCI-H345 or NCI-H510 cells. The increase was concentration dependent with 1 nM BN half-maximally increasing c-fos mRNA. Also, the increase in c-fos mRNA caused by BN was time dependent, being maximal after 1 h and returning to basal values after 4 h. GRP and GRP(14-27) but not GRP(1-16) increased c-fos mRNA. BW2258U89 (1 microM), a GRP receptor antagonist, had no effect on basal c-fos but inhibited the increase in c-fos mRNA caused by 10 nM BN. Also, BN transiently increased c-jun mRNA twofold and the increase caused by BN was blocked by BW2258U89. These data suggest that GRP receptors may regulate nuclear oncogene gene expression in SCLC cells.

Bombesin↗
PubMed1993

Cooperation between retinoic acid and phorbol esters enhances human teratocarcinoma differentiation.

This study explored cooperation between the retinoic acid (RA) and protein kinase C (PKC) pathways during differentiation of the multipotential human teratocarcinoma (TC) cell line NTERA-2 clone D1 (abbreviated NT2/D1). We report here that, compared to RA treatment alone, RA combined with the PKC stimulator 12-O-tetradecanoylphorbol-13-acetate (TPA) enhanced the regulated expression of the immunophenotypic differentiation markers SSEA-3, a globo-series carbohydrate, and the ganglio-series carbohydrate antigens GD2 and GD3. Northern analysis and transient transfection assays revealed that TPA co-treatment augmented the RA-induced expression and activation of the RA nuclear receptor-beta (RAR-beta), one early marker of RA response in NT2/D1 cells. This finding was extended with transient co-transfection experiments using a PKC-alpha expression vector which revealed that the PKC pathway can augment the activation of RAR-beta by RA. These experiments establish PKC as a modulator of RAR-beta expression in NT2/D1 cells. Similarly, experiments showed that RA can modulate activation of the PKC-responsive AP-1 complex, a transcription factor rapidly activated by TPA. Northern analysis and transient transfection assays revealed that, compared to TPA treatment alone, RA and TPA augmented the expression and transcriptional activity of AP-1 in NT2/D1 cells. In contrast, transient transfection assays revealed no cooperative effect between RA and TPA in HeLa cells, indicating that this effect in NT2/D1 cells is cell type-specific. In summary, these studies show that stimulation of the PKC second messenger pathway can modulate tumor differentiation and transcriptional activation of a retinoid receptor associated with RA response.

Biomarkers↗
PubMed1991

Oncogenic and transcriptional cooperation with Ha-Ras requires phosphorylation of c-Jun on serines 63 and 73.

Recent advances indicate a link between tumour promoters, transformation, and AP-1 activity. Protein kinase C activation increases AP-1 DNA-binding activity independently of new protein synthesis. AP-1 is also stimulated by transforming oncoproteins and growth factors. These proteins are thought to participate in a signalling cascade affecting the nuclear AP-1 complex composed of the Jun and Fos proteins. Because c-Jun is the most potent transactivator in the AP-1 complex and is elevated in Ha-ras-transformed cells, in which c-Fos is downregulated, we focused on it as a potential target. c-Jun could convert input from an oncogenic signalling cascade into changes in gene expression. Indeed, transformation of rat embryo fibroblasts by c-Jun requires an intact transcriptional activation domain and cooperation with oncogenic Ha-ras. Expression of oncogenic Ha-ras augments transactivation by c-Jun and stimulates its phosphorylation. Here we describe the mapping of the Ha-ras-responsive phosphorylation sites to serines 63 and 73 of c-Jun. Site-directed mutagenesis indicates that phosphorylation of these serines is essential for stimulation of c-Jun activity and for cooperation with Ha-ras in ocogenic transformation.

3T3 Cells↗
PubMed1988

Structure and expression of the human L-myc gene reveal a complex pattern of alternative mRNA processing.

We analyzed in detail the structure of the L-myc gene isolated from human placental DNA and characterized its expression in several small-cell lung cancer cell lines. The gene is composed of three exons and two introns spanning 6.6 kilobases in human DNA. Several distinct mRNA species are produced in all small-cell lung cancer cell lines that express L-myc. These transcripts are generated from a single gene by alternative splicing of introns 1 and 2 and by use of alternative polyadenylation signals. In some mRNAs there is a long open reading frame with a predicted translated protein of 364 residues. Amino acid sequence comparison with c-myc and N-myc demonstrated multiple discrete regions with extensive homology. In contrast, other mRNA transcripts, generated by alternative processing, could encode a truncated protein with a novel carboxy-terminal end.

Amino Acid Sequence↗
PubMed1988

The human L-myc gene encodes multiple nuclear phosphoproteins from alternatively processed mRNAs.

The human proto-oncogene L-myc generates at least four different mRNAs by alternative RNA processing. We have identified two phosphorylated L-myc proteins with molecular masses of 60,000 and 66,000 daltons [p60L-myc(human) and p66L-myc(human)] in a small-cell carcinoma line expressing high levels of L-myc mRNA. These proteins have a short half-life and are localized to the nuclear matrix fraction, as previously reported for the c-myc and N-myc proteins. In vitro translation experiments demonstrated that both the p60 and p66 species are encoded by a 3.9-kilobase (kb) mRNA which retains intron 1, while only the p60 protein is translated from a 3.6-kb L-myc mRNA which has had intron 1 removed. While L-myc proteins [p32L-myc(human) and p37L-myc(human)] could be synthesized in vitro from 2.2-kb mRNA templates, no such proteins were detected by immunoprecipitation in vivo. These observations suggest that alternative RNA processing of the L-myc transcript could play a role in determining the steady-state levels of the p60L-myc and p66L-myc proteins.

Humans↗
PubMed1988

Multiple mechanisms for transcriptional regulation of the myc gene family in small-cell lung cancer.

The molecular mechanisms reported to regulate the expression of myc family genes are multiple and complex and include gene amplification, transcriptional activation, transcriptional attenuation, and mRNA stability. We have investigated which of these mechanisms are responsible for the extreme variation in myc gene family mRNA levels observed in human small-cell lung cancer cell lines. In addition to gene amplification, a block to nascent mRNA chain elongation, causing attenuation of transcription, is an important regulatory mechanism controlling the steady-state levels of c-myc and L-myc mRNA. The loss of transcriptional attenuation is correlated with overexpression of these two genes in cell lines which do not show gene amplification. Expression of c-myc mRNA appears to be dependent on promoter activity and attenuator function. In contrast, regulation of expression of the N-myc gene does not involve transcriptional attenuation; steady-state mRNA levels are correlated with promoter activity as well as gene amplification. We conclude that transcriptional regulation of each member of the myc gene family is accomplished by a different assortment of complex mechanisms, including gene copy number, promoter activation, and transcriptional attenuation. Interference at multiple points in this complex regulatory process appears to be an important mechanism by which small-cell lung cancer and other human tumors evade growth control.

Carcinoma, Small Cell↗
PubMed1986

Chromosomal deletion, gene amplification, alternative processing, and autocrine growth factor production in the pathogenesis of human lung cancer.

Molecular and cell biologic studies of a large number of lung cancer cell lines of all histologic types have revealed several mechanisms active in the pathogenesis of these cells. Small cell lung cancer (also called "oat cell" lung cancer) has a deletion involving chromosome region 3p(14-23) that is confirmed by DNA restriction fragment length polymorphisms analysis (studies done in collaboration with Dr. Susan Naylor). Several lung cancers of both small cell and non-small cell type (including adeno- and squamous cell lung cancer) express the proto-oncogenes c-, N-, or L-myc, and in some cases more than one of these family members. N-myc appears restricted in its expression to the small cell lung cancer type while c-myc and L-myc can be expressed in both small cell and non-small cell lung cancers. Many lung cancers of all histologic types also express large amounts of p53, which are not correlated with the amount or type of myc gene product expressed. In small cell lung cancer, high levels of myc gene expression are usually associated with gene amplification, and not uncommonly there is rearrangement of some of the amplified copies. In non-small cell lung cancer, expression without amplification or rearrangement of myc genes is seen. In contrast, high level expression of p53 is not associated with gene amplification in any lung cancer type. In addition, to these proto-oncogenes acting at a presumed nuclear locus, there is increased expression of various ras family members and the c-raf-1 proto-oncogene (in collaboration with Dr. Ulf Rapp). Lung cancer cells in tissue culture can grow in medium without serum and few or no other growth factors added. Thus, it appears that lung cancer cells can produce their own growth factors which can act in an "autocrine" fashion. The best characterized example of this is gastrin releasing peptide (GRP, also called bombesin) produced by small cell lung cancer. In at least some small cell lung cancers, interference with GRP action by specific monoclonal antibodies results in inhibition of tumor cell growth in culture and in nude mouse xenografts. Thus, constitutively expressed GRP gene may function as a cellular oncogene under certain circumstances in small cell lung cancer. Based on these observations we are proposing to test monoclonal anti-GRP antibodies in patients.

Chromosome Deletion↗
PubMed1980

Complementation analysis of measles virus mutants isolated from persistently infected lymphoblastoid cell lines.

Human lymphoblastoid cell lines persistently infected with measles virus release a heterogeneous population of virions. At least 80% of the infectious particles were temperature sensitive for plaque formation at 39 degrees C. Plaque-purified temperature-sensitive mutants from four persistently infected human lymphoblastoid cell lines were shown to be heterogeneous with respect to efficiency of plating at 31 and 39 degrees C, as well as to antigen and RNA production at 39 degrees C. The heterogeneity was confirmed by complementation analysis in which 21 temperature-sensitive isolates were found to represent at least four of the five previously described complementation groups of measles virus. Two isolates complemented four reference temperature-sensitive mutants. These isolates either represent new complementation groups or are members of the fifth complementation group, group E. The majority of isolates were found to have multiple mutations, and group B mutants (RNA-) predominated. Two temperature-sensitive isolates were able to interfere with production of parental measles virus at both permissive and nonpermissive temperatures.

Antigens, Viral↗