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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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Expression analysis  of the SBT transgenic mice. RT-PCR expression analysis of SBT  (241-bp fragment) in a transgenic  line (SBT 68) shows expression  of the SBT construct in kidney  (K), but not in liver (Li). M, molecular weight marker; C, negative control with water replacing  cDNA; S16, internal control  (103 nt).
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Figure 5: Expression analysis of the SBT transgenic mice. RT-PCR expression analysis of SBT (241-bp fragment) in a transgenic line (SBT 68) shows expression of the SBT construct in kidney (K), but not in liver (Li). M, molecular weight marker; C, negative control with water replacing cDNA; S16, internal control (103 nt).

Mentions: In a further attempt to test the specificity of c-myc within the SBM transgene, TGF-α was selected as a substitute for c-myc because of its known mitogenic effect in fetal tissues where it is localized to the developing tubular epithelium during early nephrogenesis (36). This growth factor has also been implicated in epithelial cell proliferation in the mammary glands of TGF-α transgenic mice (13, 19). Similarly to the SBF construct, the SBT construct was produced as illustrated in Fig. 2. Five SBT transgenic lines were generated and Fig. 5 show renal transgene expression in a SBT line by RT-PCR analysis. However, the SBT transgenic lines, like the SBF lines, had no gross or microscopic abnormalities in any of the organs (lung, brain, liver, kidney, spleen) analyzed.


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)

Expression analysis  of the SBT transgenic mice. RT-PCR expression analysis of SBT  (241-bp fragment) in a transgenic  line (SBT 68) shows expression  of the SBT construct in kidney  (K), but not in liver (Li). M, molecular weight marker; C, negative control with water replacing  cDNA; S16, internal control  (103 nt).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 5: Expression analysis of the SBT transgenic mice. RT-PCR expression analysis of SBT (241-bp fragment) in a transgenic line (SBT 68) shows expression of the SBT construct in kidney (K), but not in liver (Li). M, molecular weight marker; C, negative control with water replacing cDNA; S16, internal control (103 nt).
Mentions: In a further attempt to test the specificity of c-myc within the SBM transgene, TGF-α was selected as a substitute for c-myc because of its known mitogenic effect in fetal tissues where it is localized to the developing tubular epithelium during early nephrogenesis (36). This growth factor has also been implicated in epithelial cell proliferation in the mammary glands of TGF-α transgenic mice (13, 19). Similarly to the SBF construct, the SBT construct was produced as illustrated in Fig. 2. Five SBT transgenic lines were generated and Fig. 5 show renal transgene expression in a SBT line by RT-PCR analysis. However, the SBT transgenic lines, like the SBF lines, had no gross or microscopic abnormalities in any of the organs (lung, brain, liver, kidney, spleen) analyzed.

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