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Maf1 is a novel target of PTEN and PI3K signaling that negatively regulates oncogenesis and lipid metabolism.

Palian BM, Rohira AD, Johnson SA, He L, Zheng N, Dubeau L, Stiles BL, Johnson DL - PLoS Genet. (2014)

Bottom Line: PTEN-mediated changes in Maf1 expression are mediated by PTEN acting on PI3K/AKT/FoxO1 signaling, revealing a new pathway that regulates RNA pol III-dependent genes.We further identify lipogenic enzymes as a new class of Maf1-regulated genes whereby Maf1 occupancy at the FASN promoter opposes SREBP1c-mediated transcription activation.Together, these results establish a new biological role for Maf1 as a downstream effector of PTEN/PI3K signaling and reveal that Maf1 is a key element by which this pathway co-regulates lipid metabolism and oncogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Keck School of Medicine, University of Southern California, and the Norris Comprehensive Cancer Center, Los Angeles, California, United States of America.

ABSTRACT
Maf1 was initially identified as a transcriptional repressor of RNA pol III-transcribed genes, yet little is known about its other potential target genes or its biological function. Here, we show that Maf1 is a key downstream target of PTEN that drives both its tumor suppressor and metabolic functions. Maf1 expression is diminished with loss of PTEN in both mouse models and human cancers. Consistent with its role as a tumor suppressor, Maf1 reduces anchorage-independent growth and tumor formation in mice. PTEN-mediated changes in Maf1 expression are mediated by PTEN acting on PI3K/AKT/FoxO1 signaling, revealing a new pathway that regulates RNA pol III-dependent genes. This regulatory event is biologically relevant as diet-induced PI3K activation reduces Maf1 expression in mouse liver. We further identify lipogenic enzymes as a new class of Maf1-regulated genes whereby Maf1 occupancy at the FASN promoter opposes SREBP1c-mediated transcription activation. Consistent with these findings, Maf1 inhibits intracellular lipid accumulation and increasing Maf1 expression in mouse liver abrogates diet-mediated induction of lipogenic enzymes and triglycerides. Together, these results establish a new biological role for Maf1 as a downstream effector of PTEN/PI3K signaling and reveal that Maf1 is a key element by which this pathway co-regulates lipid metabolism and oncogenesis.

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PTEN regulates Maf1 protein expression.(A) Maf1 expression is decreased in mouse cells and tissues lacking PTEN. Protein lysates were isolated from wild-type and Pten−/− MEFs; livers of 1 month old PtenloxP/loxP; Alb-Cre− (+/+; n = 4) and PtenloxP/loxP; Alb-Cre+ (−/−; n = 3) mice; and prostates of 5.2 week old PtenloxP/loxP; PB-Cre+ mice (+/+; n = 3) and PtenloxP/loxP; PB-Cre− littermate controls (−/−; n = 3). Lysates were subjected to immunoblot analysis with antibodies against the proteins indicated. Densitometry analysis revealed statistically significant changes in Maf1 expression (Student t-test, MEF p = 0.0426; liver p = 0.0097; prostate p = 0.0046) (B) Induction of wild type PTEN, but not a phosphatase defective mutant form induces Maf1 expression in cells lacking endogenous PTEN. U87 cells engineered to stably express inducible PTEN or phosphatase defective PTEN-C124S were used. Protein lysates were isolated from cells treated with 1 µg/ml doxycycline at times indicated. Immunoblot analysis was performed using antibodies as indicated. Densitometry analysis revealed significant differences between no doxycycline control and 24 and 48 hr doxycycline treatment (ANOVA, p<0.0001). Maf1 amounts were normalized to β-actin. The graphs represent quantification of 3 independent experiments. Values shown are the means ±S.E.
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pgen-1004789-g001: PTEN regulates Maf1 protein expression.(A) Maf1 expression is decreased in mouse cells and tissues lacking PTEN. Protein lysates were isolated from wild-type and Pten−/− MEFs; livers of 1 month old PtenloxP/loxP; Alb-Cre− (+/+; n = 4) and PtenloxP/loxP; Alb-Cre+ (−/−; n = 3) mice; and prostates of 5.2 week old PtenloxP/loxP; PB-Cre+ mice (+/+; n = 3) and PtenloxP/loxP; PB-Cre− littermate controls (−/−; n = 3). Lysates were subjected to immunoblot analysis with antibodies against the proteins indicated. Densitometry analysis revealed statistically significant changes in Maf1 expression (Student t-test, MEF p = 0.0426; liver p = 0.0097; prostate p = 0.0046) (B) Induction of wild type PTEN, but not a phosphatase defective mutant form induces Maf1 expression in cells lacking endogenous PTEN. U87 cells engineered to stably express inducible PTEN or phosphatase defective PTEN-C124S were used. Protein lysates were isolated from cells treated with 1 µg/ml doxycycline at times indicated. Immunoblot analysis was performed using antibodies as indicated. Densitometry analysis revealed significant differences between no doxycycline control and 24 and 48 hr doxycycline treatment (ANOVA, p<0.0001). Maf1 amounts were normalized to β-actin. The graphs represent quantification of 3 independent experiments. Values shown are the means ±S.E.

Mentions: To begin to explore how Maf1 might be regulated, we asked whether the tumor suppressor, PTEN, might control Maf1 levels. In MEFs, loss of Pten resulted in a substantial decrease in Maf1 protein levels (Fig. 1A). In tissue lysates derived from mouse models where Pten is selectively deleted in the liver or prostate, Maf1 expression was similarly decreased (Fig. 1A). The reduction in Maf1 is observed before the onset of tumors in these tissues [14], [15] indicating that the changes in Maf1 are concurrent with the loss of Pten. Consistent with a reduction in Maf1 upon loss of PTEN, induction of PTEN expression in PTEN-deficient human glioblastoma U87 cells resulted in an increase in Maf1 expression and required the phosphatase activity of PTEN (Fig. 1B). Together, these results demonstrate that PTEN regulates Maf1 expression in a variety of cell types.


Maf1 is a novel target of PTEN and PI3K signaling that negatively regulates oncogenesis and lipid metabolism.

Palian BM, Rohira AD, Johnson SA, He L, Zheng N, Dubeau L, Stiles BL, Johnson DL - PLoS Genet. (2014)

PTEN regulates Maf1 protein expression.(A) Maf1 expression is decreased in mouse cells and tissues lacking PTEN. Protein lysates were isolated from wild-type and Pten−/− MEFs; livers of 1 month old PtenloxP/loxP; Alb-Cre− (+/+; n = 4) and PtenloxP/loxP; Alb-Cre+ (−/−; n = 3) mice; and prostates of 5.2 week old PtenloxP/loxP; PB-Cre+ mice (+/+; n = 3) and PtenloxP/loxP; PB-Cre− littermate controls (−/−; n = 3). Lysates were subjected to immunoblot analysis with antibodies against the proteins indicated. Densitometry analysis revealed statistically significant changes in Maf1 expression (Student t-test, MEF p = 0.0426; liver p = 0.0097; prostate p = 0.0046) (B) Induction of wild type PTEN, but not a phosphatase defective mutant form induces Maf1 expression in cells lacking endogenous PTEN. U87 cells engineered to stably express inducible PTEN or phosphatase defective PTEN-C124S were used. Protein lysates were isolated from cells treated with 1 µg/ml doxycycline at times indicated. Immunoblot analysis was performed using antibodies as indicated. Densitometry analysis revealed significant differences between no doxycycline control and 24 and 48 hr doxycycline treatment (ANOVA, p<0.0001). Maf1 amounts were normalized to β-actin. The graphs represent quantification of 3 independent experiments. Values shown are the means ±S.E.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4263377&req=5

pgen-1004789-g001: PTEN regulates Maf1 protein expression.(A) Maf1 expression is decreased in mouse cells and tissues lacking PTEN. Protein lysates were isolated from wild-type and Pten−/− MEFs; livers of 1 month old PtenloxP/loxP; Alb-Cre− (+/+; n = 4) and PtenloxP/loxP; Alb-Cre+ (−/−; n = 3) mice; and prostates of 5.2 week old PtenloxP/loxP; PB-Cre+ mice (+/+; n = 3) and PtenloxP/loxP; PB-Cre− littermate controls (−/−; n = 3). Lysates were subjected to immunoblot analysis with antibodies against the proteins indicated. Densitometry analysis revealed statistically significant changes in Maf1 expression (Student t-test, MEF p = 0.0426; liver p = 0.0097; prostate p = 0.0046) (B) Induction of wild type PTEN, but not a phosphatase defective mutant form induces Maf1 expression in cells lacking endogenous PTEN. U87 cells engineered to stably express inducible PTEN or phosphatase defective PTEN-C124S were used. Protein lysates were isolated from cells treated with 1 µg/ml doxycycline at times indicated. Immunoblot analysis was performed using antibodies as indicated. Densitometry analysis revealed significant differences between no doxycycline control and 24 and 48 hr doxycycline treatment (ANOVA, p<0.0001). Maf1 amounts were normalized to β-actin. The graphs represent quantification of 3 independent experiments. Values shown are the means ±S.E.
Mentions: To begin to explore how Maf1 might be regulated, we asked whether the tumor suppressor, PTEN, might control Maf1 levels. In MEFs, loss of Pten resulted in a substantial decrease in Maf1 protein levels (Fig. 1A). In tissue lysates derived from mouse models where Pten is selectively deleted in the liver or prostate, Maf1 expression was similarly decreased (Fig. 1A). The reduction in Maf1 is observed before the onset of tumors in these tissues [14], [15] indicating that the changes in Maf1 are concurrent with the loss of Pten. Consistent with a reduction in Maf1 upon loss of PTEN, induction of PTEN expression in PTEN-deficient human glioblastoma U87 cells resulted in an increase in Maf1 expression and required the phosphatase activity of PTEN (Fig. 1B). Together, these results demonstrate that PTEN regulates Maf1 expression in a variety of cell types.

Bottom Line: PTEN-mediated changes in Maf1 expression are mediated by PTEN acting on PI3K/AKT/FoxO1 signaling, revealing a new pathway that regulates RNA pol III-dependent genes.We further identify lipogenic enzymes as a new class of Maf1-regulated genes whereby Maf1 occupancy at the FASN promoter opposes SREBP1c-mediated transcription activation.Together, these results establish a new biological role for Maf1 as a downstream effector of PTEN/PI3K signaling and reveal that Maf1 is a key element by which this pathway co-regulates lipid metabolism and oncogenesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Keck School of Medicine, University of Southern California, and the Norris Comprehensive Cancer Center, Los Angeles, California, United States of America.

ABSTRACT
Maf1 was initially identified as a transcriptional repressor of RNA pol III-transcribed genes, yet little is known about its other potential target genes or its biological function. Here, we show that Maf1 is a key downstream target of PTEN that drives both its tumor suppressor and metabolic functions. Maf1 expression is diminished with loss of PTEN in both mouse models and human cancers. Consistent with its role as a tumor suppressor, Maf1 reduces anchorage-independent growth and tumor formation in mice. PTEN-mediated changes in Maf1 expression are mediated by PTEN acting on PI3K/AKT/FoxO1 signaling, revealing a new pathway that regulates RNA pol III-dependent genes. This regulatory event is biologically relevant as diet-induced PI3K activation reduces Maf1 expression in mouse liver. We further identify lipogenic enzymes as a new class of Maf1-regulated genes whereby Maf1 occupancy at the FASN promoter opposes SREBP1c-mediated transcription activation. Consistent with these findings, Maf1 inhibits intracellular lipid accumulation and increasing Maf1 expression in mouse liver abrogates diet-mediated induction of lipogenic enzymes and triglycerides. Together, these results establish a new biological role for Maf1 as a downstream effector of PTEN/PI3K signaling and reveal that Maf1 is a key element by which this pathway co-regulates lipid metabolism and oncogenesis.

Show MeSH
Related in: MedlinePlus