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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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bcl-2–independent c-myc–dependent apoptosis in transgenic  mice. (a) RT-PCR analysis of renal bcl-2 (280 bp fragment) and bax (311-bp fragment) expression in SBM 9 and 75, control littermates and progenies  of SBM/p53−/− matings. Comparable levels of bcl-2 (top) and bax (bottom)  are seen in all the lines studied. Similar levels are also seen for the S16 internal control. c, control reaction with water replacing cDNA, M, molecular  weight marker. (b) RT-PCR expression analysis for the SBB transgene  (280-bp fragment) for four different SBB lines (10, 11, 17, and 20) is shown  in kidney (K) and other organs (Lu, lung; S, spleen; B, brain; Li, liver; C,  control). A (C57BL/6J × CBA/J)F1 non-transgenic kidney control is also  included. S16, internal control (103 nt).
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Figure 7: bcl-2–independent c-myc–dependent apoptosis in transgenic mice. (a) RT-PCR analysis of renal bcl-2 (280 bp fragment) and bax (311-bp fragment) expression in SBM 9 and 75, control littermates and progenies of SBM/p53−/− matings. Comparable levels of bcl-2 (top) and bax (bottom) are seen in all the lines studied. Similar levels are also seen for the S16 internal control. c, control reaction with water replacing cDNA, M, molecular weight marker. (b) RT-PCR expression analysis for the SBB transgene (280-bp fragment) for four different SBB lines (10, 11, 17, and 20) is shown in kidney (K) and other organs (Lu, lung; S, spleen; B, brain; Li, liver; C, control). A (C57BL/6J × CBA/J)F1 non-transgenic kidney control is also included. S16, internal control (103 nt).

Mentions: It is well documented that Bcl-2, a major suppressor of apoptosis, is capable of abrogating c-myc induced apoptosis (3). Bcl-2 plays an important role in protecting different cell types from apoptotic death (26), and homozygous bcl-2 mice develop renal cysts (23). Thus, we have compared bcl-2 expression levels in renal tissue of SBM transgenic mice with those of control littermates by RT-PCR. Comparable levels of bcl-2 expression were detected in SBM lines (SBM9 and 75) and controls (Fig. 7 a, top). The bcl-2 expression in SBM mice did not change significantly over a wide age range from birth to end stage renal disease (data not shown).


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)

bcl-2–independent c-myc–dependent apoptosis in transgenic  mice. (a) RT-PCR analysis of renal bcl-2 (280 bp fragment) and bax (311-bp fragment) expression in SBM 9 and 75, control littermates and progenies  of SBM/p53−/− matings. Comparable levels of bcl-2 (top) and bax (bottom)  are seen in all the lines studied. Similar levels are also seen for the S16 internal control. c, control reaction with water replacing cDNA, M, molecular  weight marker. (b) RT-PCR expression analysis for the SBB transgene  (280-bp fragment) for four different SBB lines (10, 11, 17, and 20) is shown  in kidney (K) and other organs (Lu, lung; S, spleen; B, brain; Li, liver; C,  control). A (C57BL/6J × CBA/J)F1 non-transgenic kidney control is also  included. S16, internal control (103 nt).
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Related In: Results  -  Collection

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Figure 7: bcl-2–independent c-myc–dependent apoptosis in transgenic mice. (a) RT-PCR analysis of renal bcl-2 (280 bp fragment) and bax (311-bp fragment) expression in SBM 9 and 75, control littermates and progenies of SBM/p53−/− matings. Comparable levels of bcl-2 (top) and bax (bottom) are seen in all the lines studied. Similar levels are also seen for the S16 internal control. c, control reaction with water replacing cDNA, M, molecular weight marker. (b) RT-PCR expression analysis for the SBB transgene (280-bp fragment) for four different SBB lines (10, 11, 17, and 20) is shown in kidney (K) and other organs (Lu, lung; S, spleen; B, brain; Li, liver; C, control). A (C57BL/6J × CBA/J)F1 non-transgenic kidney control is also included. S16, internal control (103 nt).
Mentions: It is well documented that Bcl-2, a major suppressor of apoptosis, is capable of abrogating c-myc induced apoptosis (3). Bcl-2 plays an important role in protecting different cell types from apoptotic death (26), and homozygous bcl-2 mice develop renal cysts (23). Thus, we have compared bcl-2 expression levels in renal tissue of SBM transgenic mice with those of control littermates by RT-PCR. Comparable levels of bcl-2 expression were detected in SBM lines (SBM9 and 75) and controls (Fig. 7 a, top). The bcl-2 expression in SBM mice did not change significantly over a wide age range from birth to end stage renal disease (data not shown).

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