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Conference Paper: cAMP/PKA signaling enhances activity of Deleted in Liver Cancer 1 (DLC1) tumor suppressor in suppressing liver cancer tumorigenesis

TitlecAMP/PKA signaling enhances activity of Deleted in Liver Cancer 1 (DLC1) tumor suppressor in suppressing liver cancer tumorigenesis
Authors
Issue Date2012
PublisherAmerican Association for Cancer Research.
Citation
The 103rd Annual Meeting of the American Association for Cancer Research (AACR 2012), Chicago, IL., 31 March-4 April 2012. How to Cite?
AbstractDeleted in Liver Cancer 1 (DLC1) which encodes a RhoGTPase-activating protein (RhoGAP) is a tumor suppressor frequently inactivated in a wide spectrum of human cancers. The RhoGAP activity has been shown to play a predominant role in the biological activities of DLC1. It has been shown that cells with silenced DLC1 exhibit increased active RhoA level. This finding provides evidence about the activation of RhoA as the consequence of deregulated DLC1 and points to the importance of RhoGAP activity in the biological activity of DLC1. In this regard, it is important to comprehend how RhoGAP activity of DLC1 is related. Here, we show that DLC1 was robustly phosphorylated by cyclic AMP (cAMP)/Protein kinase A (PKA) signaling in cells. Phosphorylation of DLC1 was enhanced by forskolin, a known activator of PKA while suppressed when H-89, an inhibitor of PKA was added. Direct phosphorylation of DLC1 by PKA was further confirmed by the in vitro kinase assay. Using specific phospho-DLC1 antibodies, PKA was shown to phosphorylate DLC1 at S431 and S549. Functional assays demonstrate that phosphorylation at S549 plays a critical role in provoking the inhibitory activity of DLC1 in suppressing growth and motility of Ras-transduced p53 null mouse hepatoblasts. When compared with the stable clone of wild-type DLC1, stable clone of DLC1 phosphomimetic mutant, S549D, displayed a largely reduced growth of subcutaneous and orthotopic liver implanted tumors and an enhanced apoptosis. The migration and invasion rates of S549D cells were also significantly inhibited. Furthermore, S549D expression abolished stress fiber formation but failed to alter filopodia protrusions. These functional effects exerted by S549D were ascribed to the enhanced RhoGAP activity against RhoA. To further investigate the mechanism through which the RhoGAP activity is enhanced, we found that DLC1 dimerized upon S549 phosphorylation. Our findings have revealed for the first time about the regulation of RhoGAP activity of DLC1 via dimerization. Our study suggests a molecular link between PKA and DLC1/Rho pathways and underscores the importance of S549 phosphorylation in the regulation of RhoGAP activity of DLC1.
DescriptionPoster Session 6 - Topics: Molecular and Cellular Biology 29 - Poster Board: 5: abstract no. 2141
Persistent Identifierhttp://hdl.handle.net/10722/147011

 

DC FieldValueLanguage
dc.contributor.authorKo, CFen_US
dc.contributor.authorChan, LKen_US
dc.contributor.authorTse, EYTen_US
dc.contributor.authorYeung, YSen_US
dc.contributor.authorSze, KMFen_US
dc.contributor.authorNg, IOLen_US
dc.contributor.authorYam, JWPen_US
dc.date.accessioned2012-05-23T05:52:46Z-
dc.date.available2012-05-23T05:52:46Z-
dc.date.issued2012en_US
dc.identifier.citationThe 103rd Annual Meeting of the American Association for Cancer Research (AACR 2012), Chicago, IL., 31 March-4 April 2012.en_US
dc.identifier.urihttp://hdl.handle.net/10722/147011-
dc.descriptionPoster Session 6 - Topics: Molecular and Cellular Biology 29 - Poster Board: 5: abstract no. 2141-
dc.description.abstractDeleted in Liver Cancer 1 (DLC1) which encodes a RhoGTPase-activating protein (RhoGAP) is a tumor suppressor frequently inactivated in a wide spectrum of human cancers. The RhoGAP activity has been shown to play a predominant role in the biological activities of DLC1. It has been shown that cells with silenced DLC1 exhibit increased active RhoA level. This finding provides evidence about the activation of RhoA as the consequence of deregulated DLC1 and points to the importance of RhoGAP activity in the biological activity of DLC1. In this regard, it is important to comprehend how RhoGAP activity of DLC1 is related. Here, we show that DLC1 was robustly phosphorylated by cyclic AMP (cAMP)/Protein kinase A (PKA) signaling in cells. Phosphorylation of DLC1 was enhanced by forskolin, a known activator of PKA while suppressed when H-89, an inhibitor of PKA was added. Direct phosphorylation of DLC1 by PKA was further confirmed by the in vitro kinase assay. Using specific phospho-DLC1 antibodies, PKA was shown to phosphorylate DLC1 at S431 and S549. Functional assays demonstrate that phosphorylation at S549 plays a critical role in provoking the inhibitory activity of DLC1 in suppressing growth and motility of Ras-transduced p53 null mouse hepatoblasts. When compared with the stable clone of wild-type DLC1, stable clone of DLC1 phosphomimetic mutant, S549D, displayed a largely reduced growth of subcutaneous and orthotopic liver implanted tumors and an enhanced apoptosis. The migration and invasion rates of S549D cells were also significantly inhibited. Furthermore, S549D expression abolished stress fiber formation but failed to alter filopodia protrusions. These functional effects exerted by S549D were ascribed to the enhanced RhoGAP activity against RhoA. To further investigate the mechanism through which the RhoGAP activity is enhanced, we found that DLC1 dimerized upon S549 phosphorylation. Our findings have revealed for the first time about the regulation of RhoGAP activity of DLC1 via dimerization. Our study suggests a molecular link between PKA and DLC1/Rho pathways and underscores the importance of S549 phosphorylation in the regulation of RhoGAP activity of DLC1.-
dc.languageengen_US
dc.publisherAmerican Association for Cancer Research.-
dc.relation.ispartofAnnual Meeting of the American Association for Cancer Research, AACR 2012en_US
dc.titlecAMP/PKA signaling enhances activity of Deleted in Liver Cancer 1 (DLC1) tumor suppressor in suppressing liver cancer tumorigenesisen_US
dc.typeConference_Paperen_US
dc.identifier.emailKo, CF: bokcf@hku.hken_US
dc.identifier.emailChan, LK: lkchan1@hku.hken_US
dc.identifier.emailTse, EYT: sadietse@hkucc.hku.hken_US
dc.identifier.emailYeung, YS: yeungys@hku.hken_US
dc.identifier.emailSze, KMF: karensze@hkucc.hku.hken_US
dc.identifier.emailNg, IOL: iolng@hku.hken_US
dc.identifier.emailYam, JWP: judyyam@pathology.hku.hken_US
dc.identifier.authorityNg, IOL=rp00335en_US
dc.identifier.authorityYam, JWP=rp00468en_US
dc.description.naturelink_to_OA_fulltext-
dc.identifier.hkuros199725en_US
dc.publisher.placeUnited States-
dc.description.otherThe 103rd Annual Meeting of the American Association for Cancer Research (AACR), Chicago, IL., 31 March-4 April 2012.-

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