Ras Promotes Growth by Alternative Splicing-Mediated Inactivation of the KLF6 Tumor Suppressor in Hepatocellular Carcinoma

Steven Yea, Goutham Narla, Xiao Zhao, Rakhi Garg, Sigal Tal-Kremer, Eldad Hod, Augusto Villanueva, Johnny C. Loke, Mirko Tarocchi, Kunihara Akita, Senji Shirasawa, Takehiko Sasazuki, John A. Martignetti, Josep M. Llovet, Scott L. Friedman

Research output: Contribution to journalArticle

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Abstract

Background & Aims: Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer worldwide and the third most lethal. Dysregulation of alternative splicing underlies a number of human diseases, yet its contribution to liver cancer has not been explored fully. The Krüppel-like factor 6 (KLF6) gene is a zinc finger transcription factor that inhibits cellular growth in part by transcriptional activation of p21. KLF6 function is abrogated in human cancers owing to increased alternative splicing that yields a dominant-negative isoform, KLF6 splice variant 1 (SV1), which antagonizes full-length KLF6-mediated growth suppression. The molecular basis for stimulation of KLF6 splicing is unknown. Methods: In human HCC samples and cell lines, we functionally link oncogenic Ras signaling to increased alternative splicing of KLF6 through signaling by phosphatidylinositol-3 kinase and Akt, mediated by the splice regulatory protein ASF/SF2. Results: In 67 human HCCs, there is a significant correlation between activated Ras signaling and increased KLF6 alternative splicing. In cultured cells, Ras signaling increases the expression of KLF6 SV1, relative to full-length KLF6, thereby enhancing proliferation. Abrogation of oncogenic Ras signaling by small interfering RNA (siRNA) or a farnesyl-transferase inhibitor decreases KLF6 SV1 and suppresses growth. Growth inhibition by farnesyl-transferase inhibitor in transformed cell lines is overcome by ectopic expression of KLF6 SV1. Down-regulation of the splice factor ASF/SF2 by siRNA increases KLF6 SV1 messenger RNA levels. KLF6 alternative splicing is not coupled to its transcriptional regulation. Conclusions: Our findings expand the role of Ras in human HCC by identifying a novel mechanism of tumor-suppressor inactivation through increased alternative splicing mediated by an oncogenic signaling cascade.

Original languageEnglish (US)
Pages (from-to)1521-1531
Number of pages11
JournalGastroenterology
Volume134
Issue number5
DOIs
StatePublished - May 2008
Externally publishedYes

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Alternative Splicing
Hepatocellular Carcinoma
Growth
Neoplasms
Transferases
Small Interfering RNA
Phosphatidylinositol 3-Kinase
Transformed Cell Line
Zinc Fingers
Liver Neoplasms
Transcriptional Activation
Cultured Cells
Protein Isoforms
Transcription Factors
Down-Regulation
Cell Line
Messenger RNA
Genes
Proteins

ASJC Scopus subject areas

  • Gastroenterology

Cite this

Ras Promotes Growth by Alternative Splicing-Mediated Inactivation of the KLF6 Tumor Suppressor in Hepatocellular Carcinoma. / Yea, Steven; Narla, Goutham; Zhao, Xiao; Garg, Rakhi; Tal-Kremer, Sigal; Hod, Eldad; Villanueva, Augusto; Loke, Johnny C.; Tarocchi, Mirko; Akita, Kunihara; Shirasawa, Senji; Sasazuki, Takehiko; Martignetti, John A.; Llovet, Josep M.; Friedman, Scott L.

In: Gastroenterology, Vol. 134, No. 5, 05.2008, p. 1521-1531.

Research output: Contribution to journalArticle

Yea, S, Narla, G, Zhao, X, Garg, R, Tal-Kremer, S, Hod, E, Villanueva, A, Loke, JC, Tarocchi, M, Akita, K, Shirasawa, S, Sasazuki, T, Martignetti, JA, Llovet, JM & Friedman, SL 2008, 'Ras Promotes Growth by Alternative Splicing-Mediated Inactivation of the KLF6 Tumor Suppressor in Hepatocellular Carcinoma', Gastroenterology, vol. 134, no. 5, pp. 1521-1531. https://doi.org/10.1053/j.gastro.2008.02.015
Yea, Steven ; Narla, Goutham ; Zhao, Xiao ; Garg, Rakhi ; Tal-Kremer, Sigal ; Hod, Eldad ; Villanueva, Augusto ; Loke, Johnny C. ; Tarocchi, Mirko ; Akita, Kunihara ; Shirasawa, Senji ; Sasazuki, Takehiko ; Martignetti, John A. ; Llovet, Josep M. ; Friedman, Scott L. / Ras Promotes Growth by Alternative Splicing-Mediated Inactivation of the KLF6 Tumor Suppressor in Hepatocellular Carcinoma. In: Gastroenterology. 2008 ; Vol. 134, No. 5. pp. 1521-1531.
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abstract = "Background & Aims: Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer worldwide and the third most lethal. Dysregulation of alternative splicing underlies a number of human diseases, yet its contribution to liver cancer has not been explored fully. The Kr{\"u}ppel-like factor 6 (KLF6) gene is a zinc finger transcription factor that inhibits cellular growth in part by transcriptional activation of p21. KLF6 function is abrogated in human cancers owing to increased alternative splicing that yields a dominant-negative isoform, KLF6 splice variant 1 (SV1), which antagonizes full-length KLF6-mediated growth suppression. The molecular basis for stimulation of KLF6 splicing is unknown. Methods: In human HCC samples and cell lines, we functionally link oncogenic Ras signaling to increased alternative splicing of KLF6 through signaling by phosphatidylinositol-3 kinase and Akt, mediated by the splice regulatory protein ASF/SF2. Results: In 67 human HCCs, there is a significant correlation between activated Ras signaling and increased KLF6 alternative splicing. In cultured cells, Ras signaling increases the expression of KLF6 SV1, relative to full-length KLF6, thereby enhancing proliferation. Abrogation of oncogenic Ras signaling by small interfering RNA (siRNA) or a farnesyl-transferase inhibitor decreases KLF6 SV1 and suppresses growth. Growth inhibition by farnesyl-transferase inhibitor in transformed cell lines is overcome by ectopic expression of KLF6 SV1. Down-regulation of the splice factor ASF/SF2 by siRNA increases KLF6 SV1 messenger RNA levels. KLF6 alternative splicing is not coupled to its transcriptional regulation. Conclusions: Our findings expand the role of Ras in human HCC by identifying a novel mechanism of tumor-suppressor inactivation through increased alternative splicing mediated by an oncogenic signaling cascade.",
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T1 - Ras Promotes Growth by Alternative Splicing-Mediated Inactivation of the KLF6 Tumor Suppressor in Hepatocellular Carcinoma

AU - Yea, Steven

AU - Narla, Goutham

AU - Zhao, Xiao

AU - Garg, Rakhi

AU - Tal-Kremer, Sigal

AU - Hod, Eldad

AU - Villanueva, Augusto

AU - Loke, Johnny C.

AU - Tarocchi, Mirko

AU - Akita, Kunihara

AU - Shirasawa, Senji

AU - Sasazuki, Takehiko

AU - Martignetti, John A.

AU - Llovet, Josep M.

AU - Friedman, Scott L.

PY - 2008/5

Y1 - 2008/5

N2 - Background & Aims: Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer worldwide and the third most lethal. Dysregulation of alternative splicing underlies a number of human diseases, yet its contribution to liver cancer has not been explored fully. The Krüppel-like factor 6 (KLF6) gene is a zinc finger transcription factor that inhibits cellular growth in part by transcriptional activation of p21. KLF6 function is abrogated in human cancers owing to increased alternative splicing that yields a dominant-negative isoform, KLF6 splice variant 1 (SV1), which antagonizes full-length KLF6-mediated growth suppression. The molecular basis for stimulation of KLF6 splicing is unknown. Methods: In human HCC samples and cell lines, we functionally link oncogenic Ras signaling to increased alternative splicing of KLF6 through signaling by phosphatidylinositol-3 kinase and Akt, mediated by the splice regulatory protein ASF/SF2. Results: In 67 human HCCs, there is a significant correlation between activated Ras signaling and increased KLF6 alternative splicing. In cultured cells, Ras signaling increases the expression of KLF6 SV1, relative to full-length KLF6, thereby enhancing proliferation. Abrogation of oncogenic Ras signaling by small interfering RNA (siRNA) or a farnesyl-transferase inhibitor decreases KLF6 SV1 and suppresses growth. Growth inhibition by farnesyl-transferase inhibitor in transformed cell lines is overcome by ectopic expression of KLF6 SV1. Down-regulation of the splice factor ASF/SF2 by siRNA increases KLF6 SV1 messenger RNA levels. KLF6 alternative splicing is not coupled to its transcriptional regulation. Conclusions: Our findings expand the role of Ras in human HCC by identifying a novel mechanism of tumor-suppressor inactivation through increased alternative splicing mediated by an oncogenic signaling cascade.

AB - Background & Aims: Hepatocellular carcinoma (HCC) is the fifth most prevalent cancer worldwide and the third most lethal. Dysregulation of alternative splicing underlies a number of human diseases, yet its contribution to liver cancer has not been explored fully. The Krüppel-like factor 6 (KLF6) gene is a zinc finger transcription factor that inhibits cellular growth in part by transcriptional activation of p21. KLF6 function is abrogated in human cancers owing to increased alternative splicing that yields a dominant-negative isoform, KLF6 splice variant 1 (SV1), which antagonizes full-length KLF6-mediated growth suppression. The molecular basis for stimulation of KLF6 splicing is unknown. Methods: In human HCC samples and cell lines, we functionally link oncogenic Ras signaling to increased alternative splicing of KLF6 through signaling by phosphatidylinositol-3 kinase and Akt, mediated by the splice regulatory protein ASF/SF2. Results: In 67 human HCCs, there is a significant correlation between activated Ras signaling and increased KLF6 alternative splicing. In cultured cells, Ras signaling increases the expression of KLF6 SV1, relative to full-length KLF6, thereby enhancing proliferation. Abrogation of oncogenic Ras signaling by small interfering RNA (siRNA) or a farnesyl-transferase inhibitor decreases KLF6 SV1 and suppresses growth. Growth inhibition by farnesyl-transferase inhibitor in transformed cell lines is overcome by ectopic expression of KLF6 SV1. Down-regulation of the splice factor ASF/SF2 by siRNA increases KLF6 SV1 messenger RNA levels. KLF6 alternative splicing is not coupled to its transcriptional regulation. Conclusions: Our findings expand the role of Ras in human HCC by identifying a novel mechanism of tumor-suppressor inactivation through increased alternative splicing mediated by an oncogenic signaling cascade.

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