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- Bergö, Martin, 1970, et al.
(författare)
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Inactivation of Icmt inhibits transformation by oncogenic K-Ras and B-Raf
- 2004
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Ingår i: J Clin Invest. ; 113:4, s. 539-550
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Tidskriftsartikel (refereegranskat)abstract
- Isoprenylcysteine carboxyl methyltransferase (Icmt) methylates the carboxyl-terminal isoprenylcysteine of CAAX proteins (e.g., Ras and Rho proteins). In the case of the Ras proteins, carboxyl methylation is important for targeting of the proteins to the plasma membrane. We hypothesized that a knockout of Icmt would reduce the ability of cells to be transformed by K-Ras. Fibroblasts harboring a floxed Icmt allele and expressing activated K-Ras (K-Ras-Icmt(flx/flx)) were treated with Cre-adenovirus, producing K-Ras-Icmt(Delta/Delta) fibroblasts. Inactivation of Icmt inhibited cell growth and K-Ras-induced oncogenic transformation, both in soft agar assays and in a nude mice model. The inactivation of Icmt did not affect growth factor-stimulated phosphorylation of Erk1/2 or Akt1. However, levels of RhoA were greatly reduced as a consequence of accelerated protein turnover. In addition, there was a large Ras/Erk1/2-dependent increase in p21(Cip1), which was probably a consequence of the reduced levels of RhoA. Deletion of p21(Cip1) restored the ability of K-Ras-Icmt(Delta/Delta) fibroblasts to grow in soft agar. The effect of inactivating Icmt was not limited to the inhibition of K-Ras-induced transformation: inactivation of Icmt blocked transformation by an oncogenic form of B-Raf (V599E). These studies identify Icmt as a potential target for reducing the growth of K-Ras- and B-Raf-induced malignancies.
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- Bergö, Martin, 1970, et al.
(författare)
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On the physiological importance of endoproteolysis of CAAX proteins: heart-specific RCE1 knockout mice develop a lethal cardiomyopathy
- 2004
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Ingår i: J Biol Chem. ; 279:6, s. 4729-4736
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Tidskriftsartikel (refereegranskat)abstract
- Proteins terminating with a CAAX motif, such as the Ras proteins and the nuclear lamins, undergo post-translational modification of a C-terminal cysteine with an isoprenyl lipid via a process called protein prenylation. After prenylation, the last three residues of CAAX proteins are clipped off by Rce1, an integral membrane endoprotease of the endoplasmic reticulum. Prenylation is crucial to the function of many CAAX proteins, but the physiologic significance of endoproteolytic processing has remained obscure. To address this issue, we used Cre/loxP recombination techniques to create mice lacking Rce1 in the heart, an organ where Rce1 is expressed at particularly high levels. The hearts from heart-specific Rce1 knockout mice manifested reduced levels of both the Rce1 mRNA and CAAX endoprotease activity, and the hearts manifested an accumulation of CAAX protein substrates. The heart-specific Rce1 knockout mice initially appeared healthy but died starting at 3-5 months of age. By 10 months of age, approximately 70% of the mice had died. Pathological studies revealed that the heart-specific Rce1 knockout mice had a dilated cardiomyopathy. By contrast, liver-specific Rce1 knockout mice appeared healthy, had normal transaminase levels, and had normal liver histology. These studies indicate that the endoproteolytic processing of CAAX proteins is essential for cardiac function but is less important for the liver.
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- Fong, L. G., et al.
(författare)
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Heterozygosity for Lmna deficiency eliminates the progeria-like phenotypes in Zmpste24-deficient mice
- 2004
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Ingår i: Proc Natl Acad Sci U S A. ; 101:52, s. 18111-18116
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Tidskriftsartikel (refereegranskat)abstract
- Zmpste24 is a metalloproteinase required for the processing of prelamin A to lamin A, a structural component of the nuclear lamina. Zmpste24 deficiency results in the accumulation of prelamin A within cells, a complete loss of mature lamin A, and misshapen nuclear envelopes. Zmpste24-deficient (Zmpste24(-/-)) mice exhibit retarded growth, alopecia, micrognathia, dental abnormalities, osteolytic lesions in bones, and osteoporosis, which are phenotypes shared with Hutchinson-Gilford progeria syndrome, a human disease caused by the synthesis of a mutant prelamin A that cannot undergo processing to lamin A. Zmpste24(-/-) mice also develop muscle weakness. We hypothesized that prelamin A might be toxic and that its accumulation in Zmpste24(-/-) mice is responsible for all of the disease phenotypes. We further hypothesized that Zmpste24(-/-) mice with half-normal levels of prelamin A (Zmpste24(-/-) mice with one Lmna knockout allele) would be subjected to less toxicity and be protected from disease. Thus, we bred and analyzed Zmpste24(-/-)Lmna(+/-) mice. As expected, prelamin A levels in Zmpste24(-/-)Lmna(+/-) cells were significantly reduced. Zmpste24(-/-)Lmna(+/-) mice were entirely normal, lacking all disease phenotypes, and misshapen nuclei were less frequent in Zmpste24(-/-)Lmna(+/-) cells than in Zmpste24(-/-) cells. These data suggest that prelamin A is toxic and that reducing its levels by as little as 50% provides striking protection from disease.
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- Vergnes, L., et al.
(författare)
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Lamin B1 is required for mouse development and nuclear integrity
- 2004
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Ingår i: Proc Natl Acad Sci U S A. ; 101:28, s. 10428-10433
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Tidskriftsartikel (refereegranskat)abstract
- Lamins are key structural components of the nuclear lamina, an intermediate filament meshwork that lies beneath the inner nuclear membrane. Lamins play a role in nuclear architecture, DNA replication, and gene expression. Mutations affecting A-type lamins have been associated with a variety of human diseases, including muscular dystrophy, cardiomyopathy, lipodystrophy, and progeria, but mutations in B-type lamins have never been identified in humans or in experimental animals. To investigate the in vivo function of lamin B1, the major B-type lamin, we generated mice with an insertional mutation in Lmnb1. The mutation resulted in the synthesis of a mutant lamin B1 protein lacking several key functional domains, including a portion of the rod domain, the nuclear localization signal, and the CAAX motif (the carboxyl-terminal signal for farnesylation). Homozygous Lmnb1 mutant mice survived embryonic development but died at birth with defects in lung and bone. Fibroblasts from mutant embryos grew under standard cell-culture conditions but displayed grossly misshapen nuclei, impaired differentiation, increased polyploidy, and premature senescence. Thus, the lamin B1 mutant mice provide evidence for a broad and nonredundant function of lamin B1 in mammalian development. These mutant mice and cell lines derived from them will be useful models for studying the role of the nuclear lamina in various cellular processes.
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