| 1. |
- Pasche, Boris, et al.
(författare)
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Somatic acquisition and signaling of TGFBR1*6A in cancer
- 2005
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Ingår i: Journal of the American Medical Association (JAMA). - : American Medical Association (AMA). - 0098-7484 .- 1538-3598. ; 294:13, s. 1634-1646
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Tidskriftsartikel (refereegranskat)abstract
- Context: TGFBR1*6A is a common polymorphism of the type I transforming growth factor 0 receptor (TGFBR1). Epidemiological studies suggest that TGFBR1*6A may act as a tumor susceptibility allele. How TGFBR1*6A contributes to cancer development is largely unknown.. Objectives: To determine whether TGFBR1*6A is somatically acquired by primary tumors and metastases during cancer development and whether the 3-amino acid deletion that differentiates TGFBR1*6A from TGFBR1 is part of the mature receptor or part of the signal sequence and to investigate TGFBR1*6A signaling in cancer cells. Design, Setting, and Patients: Tumor And germline tissues from 531 patients with a diagnosis of head and neck, colorectal, or breast cancer recruited from 3 centers in the United States and from 1 center in Spain from June 1, 1994, through June 30, 2004, In vitro translation assays, MCF-7 breast cancer cells stably transfected with TGFBR1*6A, TGFBR1, or the vector alone, DLD-1 colorectal cancer cells that endogenously carry TGFBR1*6A, and SW48 colorectal cancer cells that do not carry TGFBR1*6A. Main Outcome Measures: TGFBR1*6A somatic acquisition in cancer. Determination of the amino terminus of the mature TGFBR1*6A and TGFBR1 receptors. Determination of TGF-beta-dependent cell proliferation. Results: TGFBR1*6A was somatically acquired in 13 of 44 (29.5%) colorectal cancer metastases, in 4 of 157 (2.5%) of colorectal tumors, in 4 of 226 (1.8%) head and neck primary tumors, and in none of the 104 patients with breast cancer. TGFBR1*6A somatic acquisition is not associated with loss of heterozygosity, microsatellite instability, or a mutator phenotype. The signal sequences of TGFBR1 and TGFBR1*6A are cleaved at the same site resulting in identical mature receptors. TGFBR1*6A may switch TGF-beta growth inhibitory signals into growth stimulatory signals in MCF-7 breast cancer cells and in DLD-1 colorectal cancer cells. Conclusions: TGFBR1*6A is somatically acquired in 29.5% of liver metastases from colorectal cancer and may bestow cancer cells with a growth advantage in the presence of TGF-beta. The functional consequences of this conversion appear to be mediated by the TGFBR1*6A signal sequence rather than by the mature receptor. The results highlight a new facet of TGF-beta signaling in cancer and suggest that TGFBR1*6A may represent a potential therapeutic target in cancer.
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| 2. |
- Hessa, Tara, et al.
(författare)
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Molecular code for transmembrane-helix recognition by the Sec61 translocon
- 2007
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 450:7172, s. 1026-1030
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Tidskriftsartikel (refereegranskat)abstract
- Transmembrane alpha-helices in integral membrane proteins are recognized co-translationally and inserted into the membrane of the endoplasmic reticulum by the Sec61 translocon. A full quantitative description of this phenomenon, linking amino acid sequence to membrane insertion efficiency, is still lacking. Here, using in vitro translation of a model protein in the presence of dog pancreas rough microsomes to analyse a large number of systematically designed hydrophobic segments, we present a quantitative analysis of the position- dependent contribution of all 20 amino acids to membrane insertion efficiency, as well as of the effects of transmembrane segment length and flanking amino acids. The emerging picture of translocon- mediated transmembrane helix assembly is simple, with the critical sequence characteristics mirroring the physical properties of the lipid bilayer.
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| 3. |
- Jaud, Simon, et al.
(författare)
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Insertion of short transmembrane helices by the Sec61 translocon
- 2009
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:28, s. 11588-11593
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Tidskriftsartikel (refereegranskat)abstract
- The insertion efficiency of transmembrane (TM) helices by the Sec61 translocon depends on helix amino acid composition, the positions of the amino acids within the helix, and helix length. We have used an in vitro expression system to examine systematically the insertion efficiency of short polyleucine segments (L(n), n = 4 ... 12) flanked at either end by 4-residue sequences of the form XXPX-L(n)-XPXX with X = G, N, D, or K. Except for X = K, insertion efficiency (p) is <10% for n < 8, but rises steeply to 100% for n = 12. For X = K, p is already close to 100% for n = 10. A similar pattern is observed for synthetic peptides incorporated into oriented phospholipid bilayer arrays, consistent with the idea that recognition of TM segments by the translocon critically involves physical partitioning of nascent peptide chains into the lipid bilayer. Molecular dynamics simulations suggest that insertion efficiency is determined primarily by the energetic cost of distorting the bilayer in the vicinity of the TM helix. Very short lysine-flanked leucine segments can reduce the energetic cost by extensive hydrogen bonding with water and lipid phosphate groups (snorkeling) and by partial unfolding.
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| 4. |
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| 5. |
- Meindl-Beinker, Nadia M., et al.
(författare)
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Asn- and Asp-mediated interactions between transmembrane helices during translocon-mediated membrane protein assembly
- 2006
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Ingår i: EMBO reports. - : EMBO. - 1469-221X .- 1469-3178. ; 7:11, s. 1111-1116
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Tidskriftsartikel (refereegranskat)abstract
- Inter-helix hydrogen bonding involving asparagine (Asn, N), glutamine (Gin, Q), aspartic acid (Asp, D) or glutamic acid (Glu, E) can drive efficient di- or trimerization of transmembrane helices in detergent micelles and lipid bilayers. Likewise, Asn-Asn and Asp-Asp pairs can promote the formation of helical hairpins during translocon-mediated membrane protein assembly in the endoplasmic reticulum. By in vitro translation of model integral membrane protein constructs in the presence of rough microsomes, we show that Asn- or Asp-mediated interactions with a neighbouring transmembrane helix can enhance the membrane insertion efficiency of a marginally hydrophobic transmembrane segment. Our observations suggest that inter-helix hydrogen bonds can form during Sec61 translocon-assisted insertion and thus could be important for membrane protein assembly.
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