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Autophagy Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/kaup20
Blocking tumor growth by targeting autophagy and SQSTM1 in vivo a
b
Huijun Wei & Jun-Lin Guan a
Ohio State University Comprehensive Cancer Center; Columbus, OH, USA
b
Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati, OH, USA Published online: 28 May 2015.
Click for updates To cite this article: Huijun Wei & Jun-Lin Guan (2015) Blocking tumor growth by targeting autophagy and SQSTM1 in vivo, Autophagy, 11:5, 854-855, DOI: 10.1080/15548627.2015.1048173 To link to this article: http://dx.doi.org/10.1080/15548627.2015.1048173
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
AUTOPHAGIC PUNCTUM Autophagy 11:5, 854--855; May 2015; © 2015 Taylor & Francis Group, LLC
Blocking tumor growth by targeting autophagy and SQSTM1 in vivo Huijun Wei1 and Jun-Lin Guan2,* 1
Ohio State University Comprehensive Cancer Center; Columbus, OH USA; 2Department of Cancer Biology; University of Cincinnati College of Medicine;
Cincinnati, OH USA
A Downloaded by [New York University] at 07:08 29 May 2015
utophagy is a highly conserved cellular process for degradation of bulk cytoplasmic materials in response to starvation and maintenance of cellular homeostasis. Dysfunction of autophagy is implicated in a variety of diseases including cancer. In a recent study, we devised a system for inducible deletion of an essential autophagy gene Rb1cc1/ Fip200 in established tumor cells in vivo and showed that Rb1cc1 is required for maintaining tumor growth. We further investigated the role of the accumulated SQSTM1 in Rb1cc1-null autophagy-deficient tumor cells. To our surprise, the increased SQSTM1 was not responsible for the inhibition of tumor growth, but rather supported the residual growth of tumors (i.e., partially compensated for the defective growth caused by Rb1cc1 deletion). Further analysis indicated that SQSTM1 promoted tumor growth in autophagy-deficient cells at least partially through its activation of the NFKB signaling pathway. A working model is proposed to account for our findings, which suggest that targeting both autophagy and the consequently increased SQSTM1 may be exploited for developing more effective cancer therapies.
Keywords: autophagy, mouse models, SQSTM1, targeted cancer therapy, tumor growth *Correspondence [email protected]
to:
Jun-Lin
Guan;
Email:
Submitted: 08/27/2014 Revised: 09/24/2014 Accepted: 09/24/2014 http://dx.doi.org/10.1080/15548627.2015.1048173 854
Autophagy is a highly conserved process in which bulk cytoplasmic materials are sequestered and delivered to lysosomes for degradation. Besides its recycling function in nutrient or energy starvation, autophagy is increasingly recognized as a quality control mechanism for cellular homeostasis. Under various stress conditions, autophagy is activated to clear protein aggregates, impaired organelles, and intracellular pathogens. Dysfunctions in autophagy have been Autophagy
associated with different diseases including neurodegenerative diseases, inflammatory diseases, and cancers. Due to its impacts on a multitude of cellular functions, autophagy has been shown to play both tumor suppressive and promoting functions under different contexts and in different models. RB1CC1/FIP200 encodes a highly conserved protein, which is a component of the ULK1-ATG13-RB1CC1/ FIP200 complex essential for the induction of mammalian autophagy. In a previous study, we showed that conditional knockout (cKO) of Rb1cc1 decreased mammary tumor growth and metastasis driven by the PyMT oncoprotein, thus providing the first evidence for a pro-tumorigenic role for autophagy in animals with an intact immune system. Nevertheless, one limitation of the study is that autophagy is inactivated before tumor development (i.e., cKO of autophagy genes in the embryonic stage when a particular Cre is expressed). Therefore, this and several other recent studies using similar strategies to delete other autophagy genes such as Atg5 or Atg7 in lung and pancreatic cancers cannot precisely evaluate the role of autophagy in established tumors, which is particularly relevant information for targeting autophagy in cancer therapy (i.e., blocking autophagy after detection of tumors). To overcome this limitation in previous studies and evaluate the role of autophagy in established tumors, we designed an inducible system to delete Rb1cc1 after tumor development in vivo in the recent study under discussion. Using this system, we demonstrated that acute disruption of autophagy by Rb1cc1 deletion in established tumors Volume 11 Issue 5
Downloaded by [New York University] at 07:08 29 May 2015
studies, our recent results were the first to demonstrate its specific role in autophagy-deficient tumor cells. Therefore SQSTM1 accumulation can be viewed as (perhaps part of) tumor cell compensatory changes for autophagy inhibition. Besides its role as a receptor in autophagy, SQSTM1 has been shown to regulate a number of other intracellular signaling pathways. Our further analFigure 1. Autophagy deficiency caused by Rb1cc1 deletion in established tumors causes decreased proliferation ysis showed that SQSTM1 and increased apoptosis, which contribute to tumor inhibition. However, SQSTM1 accumulates after autophagy dispromotes tumor growth in ruption. Increased SQSTM1 can stimulate tumor growth under the background of autophagy deficiency by upreguautophagy-deficient cells at lating NFKB and other pathways. Therefore, further inhibition of the SQSTM1 pathway once autophagy is disrupted will cause a synergistic effect on tumor inhibition. least partially through its activation of the NFKB signaling pathway. Future from transformed MEFs as well as autophagy-deficient tumor cells was not studies will be needed to determine PyMT-driven mammary tumor cells clear. We therefore generated tumor cells whether other pathways affected by dramatically blocks their growth in with inducible Sqstm1 knockdown as SQSTM1 may also play a role, and if vivo. These results clearly show a posi- well as Rb1cc1 cKO. To our surprise, we so, how the various pathways collaborate tive role for autophagy in tumor growth found that Sqstm1 knockdown does not in mediating the function of SQSTM1 and further validate the rationale to use rescue the reduced tumor growth upon in promoting tumor growth in autophautophagy inhibitors in the design of Rb1cc1 deletion, but rather further agy-deficient cells. It will be particularly decreases their growth in vivo. Con- interesting to determine whether the novel cancer therapies. We then focused on investigating the versely, we also showed that inducible KEAP1-NFE2L2/Nrf2 pathway is mechanisms of the reduced tumor re-expression of Sqstm1 in Sqstm1 KO involved in mediating SQSTM1 action growth upon autophagy inhibition, espe- cells enhances the growth of Rb1cc1- in our system, as this has been shown to cially the potential role of accumulation null, autophagy-deficient tumors, but be responsible for the liver phenotypes of SQSTM1 observed in Rb1cc1 cKO has little effect on autophagy-competent caused by SQSTM1 accumulation in tumor cells. SQSTM1 is an autophagy tumors without Rb1cc1 deletion. These autophagy-deficient cells. receptor molecule, but is also implicated results indicated that accumulated Overall, as shown in a working in the regulation of various intracellular SQSTM1 in Rb1cc1 cKO tumor cells is model (Fig. 1), our recent studies prosignaling pathways. SQSTM1 localizes not responsible for their decreased vide the evidence that autophagy is to sites of autophagosome formation tumor growth, but rather may contrib- required for established tumor growth, and serves as a receptor by binding to ute to the residual growth of autophagy- and increased SQSTM1 contributes to LC3 on the phagophore membranes and deficient tumors. These findings raise the growth of autophagy-deficient ubiquitinated cargo proteins. SQSTM1 the interesting possibility of targeting tumors at least partially through its regitself is also an autophagy substrate, and both autophagy and SQSTM1 for ulation of the NFKB pathway. Theretherefore accumulates as protein aggre- potentially more effective cancer fore, targeting both autophagy and gates in autophagy-deficient cells. How- therapies. the consequently elevated SQSTM1 Although SQSTM1 expression has may be exploited to develop potentially ever, the pathophysiological significance of this increased SQSTM1 expression in been linked to tumor growth in previous more effective cancer therapies.
www.tandfonline.com
Autophagy
855
Autophagy Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/kaup20
Blocking tumor growth by targeting autophagy and SQSTM1 in vivo a
b
Huijun Wei & Jun-Lin Guan a
Ohio State University Comprehensive Cancer Center; Columbus, OH, USA
b
Department of Cancer Biology; University of Cincinnati College of Medicine; Cincinnati, OH, USA Published online: 28 May 2015.
Click for updates To cite this article: Huijun Wei & Jun-Lin Guan (2015) Blocking tumor growth by targeting autophagy and SQSTM1 in vivo, Autophagy, 11:5, 854-855, DOI: 10.1080/15548627.2015.1048173 To link to this article: http://dx.doi.org/10.1080/15548627.2015.1048173
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
AUTOPHAGIC PUNCTUM Autophagy 11:5, 854--855; May 2015; © 2015 Taylor & Francis Group, LLC
Blocking tumor growth by targeting autophagy and SQSTM1 in vivo Huijun Wei1 and Jun-Lin Guan2,* 1
Ohio State University Comprehensive Cancer Center; Columbus, OH USA; 2Department of Cancer Biology; University of Cincinnati College of Medicine;
Cincinnati, OH USA
A Downloaded by [New York University] at 07:08 29 May 2015
utophagy is a highly conserved cellular process for degradation of bulk cytoplasmic materials in response to starvation and maintenance of cellular homeostasis. Dysfunction of autophagy is implicated in a variety of diseases including cancer. In a recent study, we devised a system for inducible deletion of an essential autophagy gene Rb1cc1/ Fip200 in established tumor cells in vivo and showed that Rb1cc1 is required for maintaining tumor growth. We further investigated the role of the accumulated SQSTM1 in Rb1cc1-null autophagy-deficient tumor cells. To our surprise, the increased SQSTM1 was not responsible for the inhibition of tumor growth, but rather supported the residual growth of tumors (i.e., partially compensated for the defective growth caused by Rb1cc1 deletion). Further analysis indicated that SQSTM1 promoted tumor growth in autophagy-deficient cells at least partially through its activation of the NFKB signaling pathway. A working model is proposed to account for our findings, which suggest that targeting both autophagy and the consequently increased SQSTM1 may be exploited for developing more effective cancer therapies.
Keywords: autophagy, mouse models, SQSTM1, targeted cancer therapy, tumor growth *Correspondence [email protected]
to:
Jun-Lin
Guan;
Email:
Submitted: 08/27/2014 Revised: 09/24/2014 Accepted: 09/24/2014 http://dx.doi.org/10.1080/15548627.2015.1048173 854
Autophagy is a highly conserved process in which bulk cytoplasmic materials are sequestered and delivered to lysosomes for degradation. Besides its recycling function in nutrient or energy starvation, autophagy is increasingly recognized as a quality control mechanism for cellular homeostasis. Under various stress conditions, autophagy is activated to clear protein aggregates, impaired organelles, and intracellular pathogens. Dysfunctions in autophagy have been Autophagy
associated with different diseases including neurodegenerative diseases, inflammatory diseases, and cancers. Due to its impacts on a multitude of cellular functions, autophagy has been shown to play both tumor suppressive and promoting functions under different contexts and in different models. RB1CC1/FIP200 encodes a highly conserved protein, which is a component of the ULK1-ATG13-RB1CC1/ FIP200 complex essential for the induction of mammalian autophagy. In a previous study, we showed that conditional knockout (cKO) of Rb1cc1 decreased mammary tumor growth and metastasis driven by the PyMT oncoprotein, thus providing the first evidence for a pro-tumorigenic role for autophagy in animals with an intact immune system. Nevertheless, one limitation of the study is that autophagy is inactivated before tumor development (i.e., cKO of autophagy genes in the embryonic stage when a particular Cre is expressed). Therefore, this and several other recent studies using similar strategies to delete other autophagy genes such as Atg5 or Atg7 in lung and pancreatic cancers cannot precisely evaluate the role of autophagy in established tumors, which is particularly relevant information for targeting autophagy in cancer therapy (i.e., blocking autophagy after detection of tumors). To overcome this limitation in previous studies and evaluate the role of autophagy in established tumors, we designed an inducible system to delete Rb1cc1 after tumor development in vivo in the recent study under discussion. Using this system, we demonstrated that acute disruption of autophagy by Rb1cc1 deletion in established tumors Volume 11 Issue 5
Downloaded by [New York University] at 07:08 29 May 2015
studies, our recent results were the first to demonstrate its specific role in autophagy-deficient tumor cells. Therefore SQSTM1 accumulation can be viewed as (perhaps part of) tumor cell compensatory changes for autophagy inhibition. Besides its role as a receptor in autophagy, SQSTM1 has been shown to regulate a number of other intracellular signaling pathways. Our further analFigure 1. Autophagy deficiency caused by Rb1cc1 deletion in established tumors causes decreased proliferation ysis showed that SQSTM1 and increased apoptosis, which contribute to tumor inhibition. However, SQSTM1 accumulates after autophagy dispromotes tumor growth in ruption. Increased SQSTM1 can stimulate tumor growth under the background of autophagy deficiency by upreguautophagy-deficient cells at lating NFKB and other pathways. Therefore, further inhibition of the SQSTM1 pathway once autophagy is disrupted will cause a synergistic effect on tumor inhibition. least partially through its activation of the NFKB signaling pathway. Future from transformed MEFs as well as autophagy-deficient tumor cells was not studies will be needed to determine PyMT-driven mammary tumor cells clear. We therefore generated tumor cells whether other pathways affected by dramatically blocks their growth in with inducible Sqstm1 knockdown as SQSTM1 may also play a role, and if vivo. These results clearly show a posi- well as Rb1cc1 cKO. To our surprise, we so, how the various pathways collaborate tive role for autophagy in tumor growth found that Sqstm1 knockdown does not in mediating the function of SQSTM1 and further validate the rationale to use rescue the reduced tumor growth upon in promoting tumor growth in autophautophagy inhibitors in the design of Rb1cc1 deletion, but rather further agy-deficient cells. It will be particularly decreases their growth in vivo. Con- interesting to determine whether the novel cancer therapies. We then focused on investigating the versely, we also showed that inducible KEAP1-NFE2L2/Nrf2 pathway is mechanisms of the reduced tumor re-expression of Sqstm1 in Sqstm1 KO involved in mediating SQSTM1 action growth upon autophagy inhibition, espe- cells enhances the growth of Rb1cc1- in our system, as this has been shown to cially the potential role of accumulation null, autophagy-deficient tumors, but be responsible for the liver phenotypes of SQSTM1 observed in Rb1cc1 cKO has little effect on autophagy-competent caused by SQSTM1 accumulation in tumor cells. SQSTM1 is an autophagy tumors without Rb1cc1 deletion. These autophagy-deficient cells. receptor molecule, but is also implicated results indicated that accumulated Overall, as shown in a working in the regulation of various intracellular SQSTM1 in Rb1cc1 cKO tumor cells is model (Fig. 1), our recent studies prosignaling pathways. SQSTM1 localizes not responsible for their decreased vide the evidence that autophagy is to sites of autophagosome formation tumor growth, but rather may contrib- required for established tumor growth, and serves as a receptor by binding to ute to the residual growth of autophagy- and increased SQSTM1 contributes to LC3 on the phagophore membranes and deficient tumors. These findings raise the growth of autophagy-deficient ubiquitinated cargo proteins. SQSTM1 the interesting possibility of targeting tumors at least partially through its regitself is also an autophagy substrate, and both autophagy and SQSTM1 for ulation of the NFKB pathway. Theretherefore accumulates as protein aggre- potentially more effective cancer fore, targeting both autophagy and gates in autophagy-deficient cells. How- therapies. the consequently elevated SQSTM1 Although SQSTM1 expression has may be exploited to develop potentially ever, the pathophysiological significance of this increased SQSTM1 expression in been linked to tumor growth in previous more effective cancer therapies.
www.tandfonline.com
Autophagy
855
