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Kaposin-B enhances the PROX1 mRNA stability during lymphatic reprogramming of vascular endothelial cells by Kaposi's sarcoma herpes virus.

Yoo J, Kang J, Lee HN, Aguilar B, Kafka D, Lee S, Choi I, Lee J, Ramu S, Haas J, Koh CJ, Hong YK - PLoS Pathog. (2010)

Bottom Line: Here, we demonstrate that the KSHV latent gene kaposin-B enhances the PROX1 mRNA stability and plays an important role in KSHV-mediated PROX1 upregulation.We found that PROX1 mRNA contains a canonical AU-rich element (ARE) in its 3'-untranslated region that promotes PROX1 mRNA turnover and that kaposin-B stimulates cytoplasmic accumulation of the ARE-binding protein HuR through activation of the p38/MK2 pathway.Together, our study demonstrates that kaposin-B plays a key role in PROX1 upregulation during lymphatic reprogramming of blood vascular endothelial cells by KSHV.

View Article: PubMed Central - PubMed

Affiliation: Department of Surgery, Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America.

ABSTRACT
Kaposi's sarcoma (KS) is the most common cancer among HIV-positive patients. Histogenetic origin of KS has long been elusive due to a mixed expression of both blood and lymphatic endothelial markers in KS tumor cells. However, we and others discovered that Kaposi's sarcoma herpes virus (KSHV) induces lymphatic reprogramming of blood vascular endothelial cells by upregulating PROX1, which functions as the master regulator for lymphatic endothelial differentiation. Here, we demonstrate that the KSHV latent gene kaposin-B enhances the PROX1 mRNA stability and plays an important role in KSHV-mediated PROX1 upregulation. We found that PROX1 mRNA contains a canonical AU-rich element (ARE) in its 3'-untranslated region that promotes PROX1 mRNA turnover and that kaposin-B stimulates cytoplasmic accumulation of the ARE-binding protein HuR through activation of the p38/MK2 pathway. Moreover, HuR binds to and stabilizes PROX1 mRNA through its ARE and is necessary for KSHV-mediated PROX1 mRNA stabilization. Together, our study demonstrates that kaposin-B plays a key role in PROX1 upregulation during lymphatic reprogramming of blood vascular endothelial cells by KSHV.

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Cytoplasmic accumulation of HuR protein by kaposin-B.(A) LECs were transfected with an expression vector for FLAG-tagged kaposin-B for 16-hours and subjected to immunofluorescent analyses for FLAG-kaposin B (red), HuR (green) and DAPI (blue). A merged image shows that kaposin-B induces cytoplasmic accumulation of HuR only in kaposin-B-expressing cell (arrows), but not in a neighboring untransfected cell (arrowhead). Bar, 20 µm. (B) A control (CTR) or a FLAG-tagged kaposin-B vector (FLAG-kapB) was transfected into LECs for 16 hours. Nuclear (N) or cytoplasmic (C) fractions were collected and subjected to western blot analyses with antibodies against HuR, lamin A/C (nuclear marker) and tubulin (cytoplasm marker). Note accumulation of HuR protein in the cytoplasmic fraction by kaposin-B.
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ppat-1001046-g006: Cytoplasmic accumulation of HuR protein by kaposin-B.(A) LECs were transfected with an expression vector for FLAG-tagged kaposin-B for 16-hours and subjected to immunofluorescent analyses for FLAG-kaposin B (red), HuR (green) and DAPI (blue). A merged image shows that kaposin-B induces cytoplasmic accumulation of HuR only in kaposin-B-expressing cell (arrows), but not in a neighboring untransfected cell (arrowhead). Bar, 20 µm. (B) A control (CTR) or a FLAG-tagged kaposin-B vector (FLAG-kapB) was transfected into LECs for 16 hours. Nuclear (N) or cytoplasmic (C) fractions were collected and subjected to western blot analyses with antibodies against HuR, lamin A/C (nuclear marker) and tubulin (cytoplasm marker). Note accumulation of HuR protein in the cytoplasmic fraction by kaposin-B.

Mentions: While HuR protein mainly resides in the nucleus, various cell stress signals activate cytoplasmic accumulation of HuR [52]. We next asked if kaposin-B activates localization of HuR protein to the cytoplasm where mRNA stability is regulated. Indeed, our immunofluorescent analyses revealed that ectopic upregulation of kaposin-B stimulated cytoplasmic mobilization of HuR protein (Figure 6A). Moreover, we harvested the cytoplasmic and nuclear fractions from control vs. kaposin-B-overexpressing LECs to quantify the amount of mobilized HuR by kaposin-B. Consistent with the immunostaining data, a significant amount of HuR protein was found to be exported to the cytoplasm (Figure 6B). Therefore, our data demonstrate that cytoplasmic accumulation of HuR protein is activated by kaposin-B, which may play an important role in PROX1 upregulation.


Kaposin-B enhances the PROX1 mRNA stability during lymphatic reprogramming of vascular endothelial cells by Kaposi's sarcoma herpes virus.

Yoo J, Kang J, Lee HN, Aguilar B, Kafka D, Lee S, Choi I, Lee J, Ramu S, Haas J, Koh CJ, Hong YK - PLoS Pathog. (2010)

Cytoplasmic accumulation of HuR protein by kaposin-B.(A) LECs were transfected with an expression vector for FLAG-tagged kaposin-B for 16-hours and subjected to immunofluorescent analyses for FLAG-kaposin B (red), HuR (green) and DAPI (blue). A merged image shows that kaposin-B induces cytoplasmic accumulation of HuR only in kaposin-B-expressing cell (arrows), but not in a neighboring untransfected cell (arrowhead). Bar, 20 µm. (B) A control (CTR) or a FLAG-tagged kaposin-B vector (FLAG-kapB) was transfected into LECs for 16 hours. Nuclear (N) or cytoplasmic (C) fractions were collected and subjected to western blot analyses with antibodies against HuR, lamin A/C (nuclear marker) and tubulin (cytoplasm marker). Note accumulation of HuR protein in the cytoplasmic fraction by kaposin-B.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2921153&req=5

ppat-1001046-g006: Cytoplasmic accumulation of HuR protein by kaposin-B.(A) LECs were transfected with an expression vector for FLAG-tagged kaposin-B for 16-hours and subjected to immunofluorescent analyses for FLAG-kaposin B (red), HuR (green) and DAPI (blue). A merged image shows that kaposin-B induces cytoplasmic accumulation of HuR only in kaposin-B-expressing cell (arrows), but not in a neighboring untransfected cell (arrowhead). Bar, 20 µm. (B) A control (CTR) or a FLAG-tagged kaposin-B vector (FLAG-kapB) was transfected into LECs for 16 hours. Nuclear (N) or cytoplasmic (C) fractions were collected and subjected to western blot analyses with antibodies against HuR, lamin A/C (nuclear marker) and tubulin (cytoplasm marker). Note accumulation of HuR protein in the cytoplasmic fraction by kaposin-B.
Mentions: While HuR protein mainly resides in the nucleus, various cell stress signals activate cytoplasmic accumulation of HuR [52]. We next asked if kaposin-B activates localization of HuR protein to the cytoplasm where mRNA stability is regulated. Indeed, our immunofluorescent analyses revealed that ectopic upregulation of kaposin-B stimulated cytoplasmic mobilization of HuR protein (Figure 6A). Moreover, we harvested the cytoplasmic and nuclear fractions from control vs. kaposin-B-overexpressing LECs to quantify the amount of mobilized HuR by kaposin-B. Consistent with the immunostaining data, a significant amount of HuR protein was found to be exported to the cytoplasm (Figure 6B). Therefore, our data demonstrate that cytoplasmic accumulation of HuR protein is activated by kaposin-B, which may play an important role in PROX1 upregulation.

Bottom Line: Here, we demonstrate that the KSHV latent gene kaposin-B enhances the PROX1 mRNA stability and plays an important role in KSHV-mediated PROX1 upregulation.We found that PROX1 mRNA contains a canonical AU-rich element (ARE) in its 3'-untranslated region that promotes PROX1 mRNA turnover and that kaposin-B stimulates cytoplasmic accumulation of the ARE-binding protein HuR through activation of the p38/MK2 pathway.Together, our study demonstrates that kaposin-B plays a key role in PROX1 upregulation during lymphatic reprogramming of blood vascular endothelial cells by KSHV.

View Article: PubMed Central - PubMed

Affiliation: Department of Surgery, Norris Comprehensive Cancer Center, Keck School of Medicine, University of Southern California, Los Angeles, California, United States of America.

ABSTRACT
Kaposi's sarcoma (KS) is the most common cancer among HIV-positive patients. Histogenetic origin of KS has long been elusive due to a mixed expression of both blood and lymphatic endothelial markers in KS tumor cells. However, we and others discovered that Kaposi's sarcoma herpes virus (KSHV) induces lymphatic reprogramming of blood vascular endothelial cells by upregulating PROX1, which functions as the master regulator for lymphatic endothelial differentiation. Here, we demonstrate that the KSHV latent gene kaposin-B enhances the PROX1 mRNA stability and plays an important role in KSHV-mediated PROX1 upregulation. We found that PROX1 mRNA contains a canonical AU-rich element (ARE) in its 3'-untranslated region that promotes PROX1 mRNA turnover and that kaposin-B stimulates cytoplasmic accumulation of the ARE-binding protein HuR through activation of the p38/MK2 pathway. Moreover, HuR binds to and stabilizes PROX1 mRNA through its ARE and is necessary for KSHV-mediated PROX1 mRNA stabilization. Together, our study demonstrates that kaposin-B plays a key role in PROX1 upregulation during lymphatic reprogramming of blood vascular endothelial cells by KSHV.

Show MeSH
Related in: MedlinePlus