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C-myc-induced apoptosis in polycystic kidney disease is Bcl-2 and p53 independent.

Trudel M, Lanoix J, Barisoni L, Blouin MJ, Desforges M, L'Italien C, D'Agati V - J. Exp. Med. (1997)

Bottom Line: No renal abnormalities were detected in 13 transgenic lines established, indicating that the PKD phenotype is dependent on functions specific to c-myc.All SBM offspring, irrespective of their p53 genotype, developed PKD with increased renal epithelial apoptotic index.We conclude that the pathogenesis of PKD is c-myc specific and involves a critical imbalance between the opposing processes of cell proliferation and apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Institut de Recherches Cliniques de Montréal, Faculté de Médecine de l'Université de Montréal, Montréal, Québec, Canada H2W 1R7.

ABSTRACT
The SBM mouse is a unique transgenic model of polycystic kidney disease (PKD) induced by the dysregulated expression of c-myc in renal tissue. In situ hybridization analysis demonstrated intense signal for the c-myc transgene overlying tubular cystic epithelium in SBM mice. Renal proliferation index in SBM kidneys was 10-fold increased over nontransgenic controls correlating with the presence of epithelial hyperplasia. The specificity of c-myc for the proliferative potential of epithelial cells was demonstrated by substitution of c-myc with the proto-oncogene c-fos or the transforming growth factor (TGF)-alpha within the same construct. No renal abnormalities were detected in 13 transgenic lines established, indicating that the PKD phenotype is dependent on functions specific to c-myc. We also investigated another well characterized function of c-myc, the regulation of apoptosis through pathways involving p53 and members of the bcl-2 family, which induce and inhibit apoptosis, respectively. The SBM kidney tissues, which overexpress c-myc, displayed a markedly elevated (10-100-fold) apoptotic index. However, no significant difference in bcl-2, bax, or p53 expression was observed in SBM kidney compared with controls. Direct proof that the heightened renal cellular apoptosis in PKD is not occurring through p53 was obtained by successive matings between SBM and p53(-/-) mice. All SBM offspring, irrespective of their p53 genotype, developed PKD with increased renal epithelial apoptotic index. In addition, overexpression of both bcl-2 and c-myc in double transgenic mice (SBB+/SBM+) also produced a similar PKD phenotype with a high apoptotic rate, showing that c-myc can bypass bcl-2 in vivo. Thus, the in vivo c-myc apoptotic pathway in SBM mice occurs through a p53- and bcl-2-independent mechanism. We conclude that the pathogenesis of PKD is c-myc specific and involves a critical imbalance between the opposing processes of cell proliferation and apoptosis.

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Schematic representation of SBF, SBT, SBB, and  SBM constructs. The SBM construct consists of the murine  c-myc gene exon 2, 3, and 3′  flanking sequences (35). All share  common regulatory elements,  SV40 enhancer (dark oval) and  β-globin promoter (stippled) cojoined as in SBM. For SBF, these  regulatory elements are linked to  the mouse genomic c-fos sequences (hatched box, exons 1-4;  solid bar, introns 2-3 and flanking  sequences). The CIIIa sea urchin  marker (dark box) was inserted  into the 3′ end, where unstable  sequences have been identified.  For SBT, the same regulatory elements are linked to the human  TGF-α cDNA (hatched box)  bound to the human growth  hormone (hGH) 3′ untranslated  region of the last exon (open box),  the polyadenylation signal and  the 3′ flanking region (hGH)  (solid bar). For the SBB, the same  regulatory elements are linked to  the human bcl-2 cDNA (hatched  box) bound to the hGH last 5 exons (open boxes, exons; solid bar,  introns), polyadenylation signal  and 3′ flanking sequences (hGH)  (solid bar).
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Figure 2: Schematic representation of SBF, SBT, SBB, and SBM constructs. The SBM construct consists of the murine c-myc gene exon 2, 3, and 3′ flanking sequences (35). All share common regulatory elements, SV40 enhancer (dark oval) and β-globin promoter (stippled) cojoined as in SBM. For SBF, these regulatory elements are linked to the mouse genomic c-fos sequences (hatched box, exons 1-4; solid bar, introns 2-3 and flanking sequences). The CIIIa sea urchin marker (dark box) was inserted into the 3′ end, where unstable sequences have been identified. For SBT, the same regulatory elements are linked to the human TGF-α cDNA (hatched box) bound to the human growth hormone (hGH) 3′ untranslated region of the last exon (open box), the polyadenylation signal and the 3′ flanking region (hGH) (solid bar). For the SBB, the same regulatory elements are linked to the human bcl-2 cDNA (hatched box) bound to the hGH last 5 exons (open boxes, exons; solid bar, introns), polyadenylation signal and 3′ flanking sequences (hGH) (solid bar).

Mentions: SBF transgenic mice carrying the SBF construct (Fig. 2) were identified by Southern blot analysis of tail DNA. Pathological examination of brain, lung, liver, spleen, and kidney showed no gross or histological abnormalities. Specifically, no PKD phenotype or epithelial hyperplasia could be identified in any of the 8 SBF transgenic lines. Unlike the SBM mice which die of renal failure by 3–4 mo of age, mice of the different SBF lines analyzed have a normal life span of 2–3 yr.


C-myc-induced apoptosis in polycystic kidney disease is Bcl-2 and p53 independent.

Trudel M, Lanoix J, Barisoni L, Blouin MJ, Desforges M, L'Italien C, D'Agati V - J. Exp. Med. (1997)

Schematic representation of SBF, SBT, SBB, and  SBM constructs. The SBM construct consists of the murine  c-myc gene exon 2, 3, and 3′  flanking sequences (35). All share  common regulatory elements,  SV40 enhancer (dark oval) and  β-globin promoter (stippled) cojoined as in SBM. For SBF, these  regulatory elements are linked to  the mouse genomic c-fos sequences (hatched box, exons 1-4;  solid bar, introns 2-3 and flanking  sequences). The CIIIa sea urchin  marker (dark box) was inserted  into the 3′ end, where unstable  sequences have been identified.  For SBT, the same regulatory elements are linked to the human  TGF-α cDNA (hatched box)  bound to the human growth  hormone (hGH) 3′ untranslated  region of the last exon (open box),  the polyadenylation signal and  the 3′ flanking region (hGH)  (solid bar). For the SBB, the same  regulatory elements are linked to  the human bcl-2 cDNA (hatched  box) bound to the hGH last 5 exons (open boxes, exons; solid bar,  introns), polyadenylation signal  and 3′ flanking sequences (hGH)  (solid bar).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199149&req=5

Figure 2: Schematic representation of SBF, SBT, SBB, and SBM constructs. The SBM construct consists of the murine c-myc gene exon 2, 3, and 3′ flanking sequences (35). All share common regulatory elements, SV40 enhancer (dark oval) and β-globin promoter (stippled) cojoined as in SBM. For SBF, these regulatory elements are linked to the mouse genomic c-fos sequences (hatched box, exons 1-4; solid bar, introns 2-3 and flanking sequences). The CIIIa sea urchin marker (dark box) was inserted into the 3′ end, where unstable sequences have been identified. For SBT, the same regulatory elements are linked to the human TGF-α cDNA (hatched box) bound to the human growth hormone (hGH) 3′ untranslated region of the last exon (open box), the polyadenylation signal and the 3′ flanking region (hGH) (solid bar). For the SBB, the same regulatory elements are linked to the human bcl-2 cDNA (hatched box) bound to the hGH last 5 exons (open boxes, exons; solid bar, introns), polyadenylation signal and 3′ flanking sequences (hGH) (solid bar).
Mentions: SBF transgenic mice carrying the SBF construct (Fig. 2) were identified by Southern blot analysis of tail DNA. Pathological examination of brain, lung, liver, spleen, and kidney showed no gross or histological abnormalities. Specifically, no PKD phenotype or epithelial hyperplasia could be identified in any of the 8 SBF transgenic lines. Unlike the SBM mice which die of renal failure by 3–4 mo of age, mice of the different SBF lines analyzed have a normal life span of 2–3 yr.

Bottom Line: No renal abnormalities were detected in 13 transgenic lines established, indicating that the PKD phenotype is dependent on functions specific to c-myc.All SBM offspring, irrespective of their p53 genotype, developed PKD with increased renal epithelial apoptotic index.We conclude that the pathogenesis of PKD is c-myc specific and involves a critical imbalance between the opposing processes of cell proliferation and apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Institut de Recherches Cliniques de Montréal, Faculté de Médecine de l'Université de Montréal, Montréal, Québec, Canada H2W 1R7.

ABSTRACT
The SBM mouse is a unique transgenic model of polycystic kidney disease (PKD) induced by the dysregulated expression of c-myc in renal tissue. In situ hybridization analysis demonstrated intense signal for the c-myc transgene overlying tubular cystic epithelium in SBM mice. Renal proliferation index in SBM kidneys was 10-fold increased over nontransgenic controls correlating with the presence of epithelial hyperplasia. The specificity of c-myc for the proliferative potential of epithelial cells was demonstrated by substitution of c-myc with the proto-oncogene c-fos or the transforming growth factor (TGF)-alpha within the same construct. No renal abnormalities were detected in 13 transgenic lines established, indicating that the PKD phenotype is dependent on functions specific to c-myc. We also investigated another well characterized function of c-myc, the regulation of apoptosis through pathways involving p53 and members of the bcl-2 family, which induce and inhibit apoptosis, respectively. The SBM kidney tissues, which overexpress c-myc, displayed a markedly elevated (10-100-fold) apoptotic index. However, no significant difference in bcl-2, bax, or p53 expression was observed in SBM kidney compared with controls. Direct proof that the heightened renal cellular apoptosis in PKD is not occurring through p53 was obtained by successive matings between SBM and p53(-/-) mice. All SBM offspring, irrespective of their p53 genotype, developed PKD with increased renal epithelial apoptotic index. In addition, overexpression of both bcl-2 and c-myc in double transgenic mice (SBB+/SBM+) also produced a similar PKD phenotype with a high apoptotic rate, showing that c-myc can bypass bcl-2 in vivo. Thus, the in vivo c-myc apoptotic pathway in SBM mice occurs through a p53- and bcl-2-independent mechanism. We conclude that the pathogenesis of PKD is c-myc specific and involves a critical imbalance between the opposing processes of cell proliferation and apoptosis.

Show MeSH
Related in: MedlinePlus