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PPARβ/δ promotes HRAS-induced senescence and tumor suppression by potentiating p-ERK and repressing p-AKT signaling.

Zhu B, Ferry CH, Blazanin N, Bility MT, Khozoie C, Kang BH, Glick AB, Gonzalez FJ, Peters JM - Oncogene (2013)

Bottom Line: PPARβ/δ expression increased p-ERK and decreased p-AKT activity.Increased p-ERK activity results from the dampened HRAS-induced negative feedback response mediated in part through transcriptional upregulation of RAS guanyl-releasing protein 1 (RASGRP1) by PPARβ/δ.Decreased p-AKT activity results from repression of integrin-linked kinase (ILK) and phosphoinositide-dependent protein kinase-1 (PDPK1) expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Veterinary and Biomedical Sciences, The Center for Molecular Toxicology and Carcinogenesis, The Pennsylvania State University, University Park, PA, USA.

ABSTRACT
Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) inhibits skin tumorigenesis through mechanisms that may be dependent on HRAS signaling. The present study examined the hypothesis that PPARβ/δ promotes HRAS-induced senescence resulting in suppression of tumorigenesis. PPARβ/δ expression increased p-ERK and decreased p-AKT activity. Increased p-ERK activity results from the dampened HRAS-induced negative feedback response mediated in part through transcriptional upregulation of RAS guanyl-releasing protein 1 (RASGRP1) by PPARβ/δ. Decreased p-AKT activity results from repression of integrin-linked kinase (ILK) and phosphoinositide-dependent protein kinase-1 (PDPK1) expression. Decreased p-AKT activity in turn promotes cellular senescence through upregulation of p53 and p27 expression. Both over-expression of RASGRP1 and shRNA-mediated knockdown of ILK partially restore cellular senescence in Pparβ/δ- cells. Higher PPARβ/δ expression is also correlated with increased senescence observed in human benign neurofibromas and colon adenoma lesions in vivo. These results demonstrate that PPARβ/δ promotes senescence to inhibit tumorigenesis and provide new mechanistic insights into HRAS-induced cellular senescence.

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PPARβ/δ attenuates ILK/p-AKT to promote senescence in mouse skin tumors. Skin tumors from wild-type (+/+) or Pparβ/δ- (−/−) mice were obtained from a complete carcinogen bioassay. (a) Immunofluorescence of p-AKT (S473), KERATIN 14 and p27 in squamous cell carcinoma (SCC) and squamous cell papillomas (SCP). Serial sections of tumor samples were also stained for β-gal and H&E. (b) Immunofluorescence of p-AKT (S473) and Ki-67. (c) Cumulative frequency of mean intensity of p-AKT (S473) from at least 1000 cells as shown in b. (d) Western blot analysis and scatter plots of p-AKT and senescence marker p16. Relative expression level of proteins was normalized to that of LDH and are shown as the relative fold change as compared to control. Red circles represent data for tumors from (−/−) mice and black circle represent data for tumors from (+/+) mice. Values represent the mean ± S.E.M.. *significantly different than (+/+) control (P ≤ 0.05).
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Figure 6: PPARβ/δ attenuates ILK/p-AKT to promote senescence in mouse skin tumors. Skin tumors from wild-type (+/+) or Pparβ/δ- (−/−) mice were obtained from a complete carcinogen bioassay. (a) Immunofluorescence of p-AKT (S473), KERATIN 14 and p27 in squamous cell carcinoma (SCC) and squamous cell papillomas (SCP). Serial sections of tumor samples were also stained for β-gal and H&E. (b) Immunofluorescence of p-AKT (S473) and Ki-67. (c) Cumulative frequency of mean intensity of p-AKT (S473) from at least 1000 cells as shown in b. (d) Western blot analysis and scatter plots of p-AKT and senescence marker p16. Relative expression level of proteins was normalized to that of LDH and are shown as the relative fold change as compared to control. Red circles represent data for tumors from (−/−) mice and black circle represent data for tumors from (+/+) mice. Values represent the mean ± S.E.M.. *significantly different than (+/+) control (P ≤ 0.05).

Mentions: To test the hypothesis that PPARβ/δ promotes HRAS-induced senescence in vivo, chemically-induced skin tumors were examined. β-gal positive regions of papillomas also stained positive for p27 but were negative for p-AKT (S473) in both wild-type and Pparβ/δ- mice (Figure 6a). SCC were negative for β-gal but exhibited strong expression of p-AKT (S473) and essentially no p27 expression (Figure 6a). Increased p-AKT staining was found in tumors from Pparβ/δ- mice compared to wild-type counterparts (Figure 6b, c). These findings are consistent with analysis of HRAS-expressing keratinocytes showing that p-AKT inhibits FOXO and p27 expression (Figure 2f, g). More Ki-67 positive cells were found in tumors from Pparβ/δ- mice as compared to tumors examined from wild-type mice (Figure 6b). This suggests that PPARβ/δ inhibits the proliferative capacity of skin tumors. Higher expression of ILK, p-AKT (S473, T308) was also found in skin tumors from Pparβ/δ- mice compared to wild-type mice (Figure 6d). Further, a negative correlation between p-AKT and the senescence marker p16 was also found (Figure 6d). These findings suggest the anti-tumorigenic role of PPARβ/δ in promoting senescence is mediated by repressing ILK/p-AKT signaling.


PPARβ/δ promotes HRAS-induced senescence and tumor suppression by potentiating p-ERK and repressing p-AKT signaling.

Zhu B, Ferry CH, Blazanin N, Bility MT, Khozoie C, Kang BH, Glick AB, Gonzalez FJ, Peters JM - Oncogene (2013)

PPARβ/δ attenuates ILK/p-AKT to promote senescence in mouse skin tumors. Skin tumors from wild-type (+/+) or Pparβ/δ- (−/−) mice were obtained from a complete carcinogen bioassay. (a) Immunofluorescence of p-AKT (S473), KERATIN 14 and p27 in squamous cell carcinoma (SCC) and squamous cell papillomas (SCP). Serial sections of tumor samples were also stained for β-gal and H&E. (b) Immunofluorescence of p-AKT (S473) and Ki-67. (c) Cumulative frequency of mean intensity of p-AKT (S473) from at least 1000 cells as shown in b. (d) Western blot analysis and scatter plots of p-AKT and senescence marker p16. Relative expression level of proteins was normalized to that of LDH and are shown as the relative fold change as compared to control. Red circles represent data for tumors from (−/−) mice and black circle represent data for tumors from (+/+) mice. Values represent the mean ± S.E.M.. *significantly different than (+/+) control (P ≤ 0.05).
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Figure 6: PPARβ/δ attenuates ILK/p-AKT to promote senescence in mouse skin tumors. Skin tumors from wild-type (+/+) or Pparβ/δ- (−/−) mice were obtained from a complete carcinogen bioassay. (a) Immunofluorescence of p-AKT (S473), KERATIN 14 and p27 in squamous cell carcinoma (SCC) and squamous cell papillomas (SCP). Serial sections of tumor samples were also stained for β-gal and H&E. (b) Immunofluorescence of p-AKT (S473) and Ki-67. (c) Cumulative frequency of mean intensity of p-AKT (S473) from at least 1000 cells as shown in b. (d) Western blot analysis and scatter plots of p-AKT and senescence marker p16. Relative expression level of proteins was normalized to that of LDH and are shown as the relative fold change as compared to control. Red circles represent data for tumors from (−/−) mice and black circle represent data for tumors from (+/+) mice. Values represent the mean ± S.E.M.. *significantly different than (+/+) control (P ≤ 0.05).
Mentions: To test the hypothesis that PPARβ/δ promotes HRAS-induced senescence in vivo, chemically-induced skin tumors were examined. β-gal positive regions of papillomas also stained positive for p27 but were negative for p-AKT (S473) in both wild-type and Pparβ/δ- mice (Figure 6a). SCC were negative for β-gal but exhibited strong expression of p-AKT (S473) and essentially no p27 expression (Figure 6a). Increased p-AKT staining was found in tumors from Pparβ/δ- mice compared to wild-type counterparts (Figure 6b, c). These findings are consistent with analysis of HRAS-expressing keratinocytes showing that p-AKT inhibits FOXO and p27 expression (Figure 2f, g). More Ki-67 positive cells were found in tumors from Pparβ/δ- mice as compared to tumors examined from wild-type mice (Figure 6b). This suggests that PPARβ/δ inhibits the proliferative capacity of skin tumors. Higher expression of ILK, p-AKT (S473, T308) was also found in skin tumors from Pparβ/δ- mice compared to wild-type mice (Figure 6d). Further, a negative correlation between p-AKT and the senescence marker p16 was also found (Figure 6d). These findings suggest the anti-tumorigenic role of PPARβ/δ in promoting senescence is mediated by repressing ILK/p-AKT signaling.

Bottom Line: PPARβ/δ expression increased p-ERK and decreased p-AKT activity.Increased p-ERK activity results from the dampened HRAS-induced negative feedback response mediated in part through transcriptional upregulation of RAS guanyl-releasing protein 1 (RASGRP1) by PPARβ/δ.Decreased p-AKT activity results from repression of integrin-linked kinase (ILK) and phosphoinositide-dependent protein kinase-1 (PDPK1) expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Veterinary and Biomedical Sciences, The Center for Molecular Toxicology and Carcinogenesis, The Pennsylvania State University, University Park, PA, USA.

ABSTRACT
Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) inhibits skin tumorigenesis through mechanisms that may be dependent on HRAS signaling. The present study examined the hypothesis that PPARβ/δ promotes HRAS-induced senescence resulting in suppression of tumorigenesis. PPARβ/δ expression increased p-ERK and decreased p-AKT activity. Increased p-ERK activity results from the dampened HRAS-induced negative feedback response mediated in part through transcriptional upregulation of RAS guanyl-releasing protein 1 (RASGRP1) by PPARβ/δ. Decreased p-AKT activity results from repression of integrin-linked kinase (ILK) and phosphoinositide-dependent protein kinase-1 (PDPK1) expression. Decreased p-AKT activity in turn promotes cellular senescence through upregulation of p53 and p27 expression. Both over-expression of RASGRP1 and shRNA-mediated knockdown of ILK partially restore cellular senescence in Pparβ/δ- cells. Higher PPARβ/δ expression is also correlated with increased senescence observed in human benign neurofibromas and colon adenoma lesions in vivo. These results demonstrate that PPARβ/δ promotes senescence to inhibit tumorigenesis and provide new mechanistic insights into HRAS-induced cellular senescence.

Show MeSH
Related in: MedlinePlus