Induction of ribosomal genes and hepatocyte hypertrophy by adenovirus-mediated expression of c-Myc in vivo - PubMed (original) (raw)

Induction of ribosomal genes and hepatocyte hypertrophy by adenovirus-mediated expression of c-Myc in vivo

S Kim et al. Proc Natl Acad Sci U S A. 2000.

Abstract

Overexpression of c-Myc in immortalized cells increases cell proliferation, inhibits cell differentiation, and promotes cell transformation. Recent evidence suggests that these effects, however, do not necessarily occur when c-Myc is overexpressed in primary mammalian cells. We sought to determine the immediate effects of transient overexpression of c-Myc in primary cells in vivo by using recombinant adenovirus to overexpress human MYC in mouse liver. Mice were intravenously injected with adenoviruses encoding MYC (Ad/Myc), E2F-1 (Ad/E2F-1), or beta-galactosidase (Ad/LacZ). Transgene expression was detectable 4 days after injection. Expression of ectopic c-Myc was immediately accompanied by enlarged and dysmorphic hepatocytes in the absence of significant cell proliferation or apoptosis. These findings were not present in the livers of mice injected with Ad/E2F-1 or Ad/LacZ. Prominent hepatocyte nuclei and nucleoli were associated with the up-regulation of large- and small-subunit ribosomal and nucleolar genes, suggesting that c-Myc may induce their expression to increase cell mass. Our studies support a role for c-Myc in the in vivo control of vertebrate cell size and metabolism independent of cell proliferation.

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Figures

Figure 1

Figure 1

(A) β-Galactosidase staining of day 5 Ad/LacZ liver. (B) (I) Northern blot showing exogenous_MYC_ gene expression starting on day 4. 18S is shown as loading control. (II) Western blot showing c-Myc protein expression in Ad/Myc livers. Coomassie staining is shown for loading control. D3, D4, and D5 indicate total RNA and protein samples isolated from Ad/Myc livers killed on days 3, 4, and 5, respectively. (C) Western blot showing that E2F-1 is expressed by day 3 postinjection of recombinant adenovirus carrying E2F-1. E2F-1 is not detectable in Ad/LacZ or Ad/Myc livers. (D) Hematoxylin/eosin staining of day 4 Ad/LacZ, Ad/Myc, and Ad/E2F-1 liver. (Magnification: A, ×5;D, ×40.)

Figure 2

Figure 2

(Left) Day 4 Ad/LacZ liver. (Right) Day 4 Ad/Myc liver. (A) Methyl green pyronin staining of the sections. The arrows highlight enlarged nucleoli of Ad/Myc hepatocytes. (B) Ki-67 staining of liver sections. The arrow indicates positive staining of a proliferating cell. (C) TUNEL staining of liver sections. The arrows indicate nuclei of cells undergoing apoptosis. (Magnification:A, ×60; B and C, ×10.)

Figure 3

Figure 3

Northern blot showing the expression levels of ribosomal and nucleolar genes in Ad/LacZ and Ad/Myc livers. All of the ribosomal genes examined show increased expression after the ectopic MYC expression. Expression of the immediate-early gene 33 is down-regulated in Ad/Myc liver. 18S is shown as loading control. Numbers at the bottom indicate the days mice were killed after adenovirus injection.

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