期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 112, 期 3, 页码 779-784出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1412811112
关键词
Ras; K-Ras; palmitoylation; alternate splicing; oncogene
资金
- National Institutes of Health [F30CA167910, CA161494, CA042978, CA178017, GM055279, CA116034]
The two products of the KRAS locus, K-Ras4A and K-Ras4B, are encoded by alternative fourth exons and therefore, possess distinct membrane-targeting sequences. The common activating mutations occur in exons 1 or 2 and therefore, render both splice variants oncogenic. K-Ras4A has been understudied, because it has been considered a minor splice variant. By priming off of the splice junction, we developed a quantitative RT-PCR assay for K-Ras4A and K-Ras4B message capable of measuring absolute amounts of the two transcripts. We found that K-Ras4A was widely expressed in 30 of 30 human cancer cell lines and amounts equal to K-Ras4B in 17 human colorectal tumors. Using splice variant-specific antibodies, we detected K-Ras4A protein in several tumor cell lines at a level equal to or greater than that of K-Ras4B. In addition to the CAAX motif, the C terminus of K-Ras4A contains a site of palmitoylation as well as a bipartite polybasic region. Although both were required for maximal efficiency, each of these could independently deliver K-Ras4A to the plasma membrane. Thus, among four Ras proteins, K-Ras4A is unique in possessing a dual membrane-targeting motif. We also found that, unlike K-Ras4B, K-Ras4A does not bind to the cytosolic chaperone delta-subunit of cGMP phosphodiesterase type 6 (PDE6d). We conclude that efforts to develop anti-K-Ras drugs that interfere with membrane trafficking will have to take into account the distinct modes of targeting of the two K-Ras splice variants.
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