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RalA suppresses early stages of Ras-induced squamous cell carcinoma progression.

Sowalsky AG, Alt-Holland A, Shamis Y, Garlick JA, Feig LA - Oncogene (2009)

Bottom Line: Conversion of Ras-expressing keratinocytes from a premalignant to malignant state induced by decreasing E-cadherin function was associated with and required an approximately two to threefold decrease in RalA expression.Knockdown of the Ral effector, Exo84, mimicked the effects of decreasing RalA levels in these engineered tissues.These results imply that an important component of the early stages in squamous carcinoma progression may be a modest decrease in RalA gene expression that magnifies the effects of decreased E-cadherin expression by promoting its degradation.

View Article: PubMed Central - PubMed

Affiliation: Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, MA 02111, USA.

ABSTRACT
Ras proteins activate Raf and PI-3 kinases, as well as exchange factors for RalA and RalB GTPases. Many previous studies have reported that the Ral-signaling cascade contributes positively to Ras-mediated oncogenesis. Here, using a bioengineered tissue model of early steps in Ras-induced human squamous cell carcinoma of the skin, we found the opposite. Conversion of Ras-expressing keratinocytes from a premalignant to malignant state induced by decreasing E-cadherin function was associated with and required an approximately two to threefold decrease in RalA expression. Moreover, direct knockdown of RalA to a similar degree by shRNA expression in these cells reduced E-cadherin levels and also induced progression to a malignant phenotype. Knockdown of the Ral effector, Exo84, mimicked the effects of decreasing RalA levels in these engineered tissues. These phenomena can be explained by our finding that the stability of E-cadherin in Ras-expressing keratinocytes depends upon this RalA signaling cascade. These results imply that an important component of the early stages in squamous carcinoma progression may be a modest decrease in RalA gene expression that magnifies the effects of decreased E-cadherin expression by promoting its degradation.

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RalA is downregulated in head and neck squamous cell carcinomaSurvey of Oncomine microarray database for RalA expression in normal and diseased tissues. Data is represented as a box-and-whiskers plot with the box representing the 1st and 3rd quartiles and the whiskers denoting the data range. Center bar denotes median. Significance cutoff is p < 1×10-4 for each cancer type compared to normal. ProAdCa: Prostate adenocarcinoma (normal, n=8; cancer n=27). HNSCC: Head and neck squamous cell carcinoma (normal, n=13; cancer n=41). GliMu: Glioblastoma multiforme (normal, n=23; cancer n=77; normal, n=7; cancer n=25;). OlDen: Oligodendroglioma (normal, n=23; cancer n=50). AstCy: Astrocytoma (normal, n=23; cancer n=26). BlaCa: Bladder carcinoma (normal, n=48; cancer n=109). BreCa: Breast Carcinoma (normal, n=7; cancer n=41).
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Figure 7: RalA is downregulated in head and neck squamous cell carcinomaSurvey of Oncomine microarray database for RalA expression in normal and diseased tissues. Data is represented as a box-and-whiskers plot with the box representing the 1st and 3rd quartiles and the whiskers denoting the data range. Center bar denotes median. Significance cutoff is p < 1×10-4 for each cancer type compared to normal. ProAdCa: Prostate adenocarcinoma (normal, n=8; cancer n=27). HNSCC: Head and neck squamous cell carcinoma (normal, n=13; cancer n=41). GliMu: Glioblastoma multiforme (normal, n=23; cancer n=77; normal, n=7; cancer n=25;). OlDen: Oligodendroglioma (normal, n=23; cancer n=50). AstCy: Astrocytoma (normal, n=23; cancer n=26). BlaCa: Bladder carcinoma (normal, n=48; cancer n=109). BreCa: Breast Carcinoma (normal, n=7; cancer n=41).

Mentions: The experiments described here have associated the early progression of SCC with the down-regulation of RalA. We sought to determine whether down-regulation of RalA occurs in the pathogenesis of SCC. A survey of the microarray database Oncomine (Rhodes et al., 2004) revealed data comparing RalA expression in a variety of cancer types with comparable normal tissues (Fig. 7). Consistent with several previously-reported results suggesting RalA plays a positive role in tumorigenesis, RalA was up-regulated in breast, bladder, brain and prostate cancer. While data for SCC of the skin was not present in this database, RalA was significantly (p < 1×10-6) down-regulated (∼30%) in head and neck squamous cell carcinoma (HNSCC) compared to normal oral mucosa. Analysis of the differentiation status of each tumor and relative RalA expression in a contingency table (Table 1) by Fisher's exact test gave p = 0.0157 strongly associated RalA down-regulation with poorly-differentiating SCC tumors (Ginos et al., 2004). RalB was reduced to a smaller degree in HNSCC but in contrast to RaA it was also reduced in some other tumor types analyzed (Supplementary Fig. 6).


RalA suppresses early stages of Ras-induced squamous cell carcinoma progression.

Sowalsky AG, Alt-Holland A, Shamis Y, Garlick JA, Feig LA - Oncogene (2009)

RalA is downregulated in head and neck squamous cell carcinomaSurvey of Oncomine microarray database for RalA expression in normal and diseased tissues. Data is represented as a box-and-whiskers plot with the box representing the 1st and 3rd quartiles and the whiskers denoting the data range. Center bar denotes median. Significance cutoff is p < 1×10-4 for each cancer type compared to normal. ProAdCa: Prostate adenocarcinoma (normal, n=8; cancer n=27). HNSCC: Head and neck squamous cell carcinoma (normal, n=13; cancer n=41). GliMu: Glioblastoma multiforme (normal, n=23; cancer n=77; normal, n=7; cancer n=25;). OlDen: Oligodendroglioma (normal, n=23; cancer n=50). AstCy: Astrocytoma (normal, n=23; cancer n=26). BlaCa: Bladder carcinoma (normal, n=48; cancer n=109). BreCa: Breast Carcinoma (normal, n=7; cancer n=41).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2803332&req=5

Figure 7: RalA is downregulated in head and neck squamous cell carcinomaSurvey of Oncomine microarray database for RalA expression in normal and diseased tissues. Data is represented as a box-and-whiskers plot with the box representing the 1st and 3rd quartiles and the whiskers denoting the data range. Center bar denotes median. Significance cutoff is p < 1×10-4 for each cancer type compared to normal. ProAdCa: Prostate adenocarcinoma (normal, n=8; cancer n=27). HNSCC: Head and neck squamous cell carcinoma (normal, n=13; cancer n=41). GliMu: Glioblastoma multiforme (normal, n=23; cancer n=77; normal, n=7; cancer n=25;). OlDen: Oligodendroglioma (normal, n=23; cancer n=50). AstCy: Astrocytoma (normal, n=23; cancer n=26). BlaCa: Bladder carcinoma (normal, n=48; cancer n=109). BreCa: Breast Carcinoma (normal, n=7; cancer n=41).
Mentions: The experiments described here have associated the early progression of SCC with the down-regulation of RalA. We sought to determine whether down-regulation of RalA occurs in the pathogenesis of SCC. A survey of the microarray database Oncomine (Rhodes et al., 2004) revealed data comparing RalA expression in a variety of cancer types with comparable normal tissues (Fig. 7). Consistent with several previously-reported results suggesting RalA plays a positive role in tumorigenesis, RalA was up-regulated in breast, bladder, brain and prostate cancer. While data for SCC of the skin was not present in this database, RalA was significantly (p < 1×10-6) down-regulated (∼30%) in head and neck squamous cell carcinoma (HNSCC) compared to normal oral mucosa. Analysis of the differentiation status of each tumor and relative RalA expression in a contingency table (Table 1) by Fisher's exact test gave p = 0.0157 strongly associated RalA down-regulation with poorly-differentiating SCC tumors (Ginos et al., 2004). RalB was reduced to a smaller degree in HNSCC but in contrast to RaA it was also reduced in some other tumor types analyzed (Supplementary Fig. 6).

Bottom Line: Conversion of Ras-expressing keratinocytes from a premalignant to malignant state induced by decreasing E-cadherin function was associated with and required an approximately two to threefold decrease in RalA expression.Knockdown of the Ral effector, Exo84, mimicked the effects of decreasing RalA levels in these engineered tissues.These results imply that an important component of the early stages in squamous carcinoma progression may be a modest decrease in RalA gene expression that magnifies the effects of decreased E-cadherin expression by promoting its degradation.

View Article: PubMed Central - PubMed

Affiliation: Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, MA 02111, USA.

ABSTRACT
Ras proteins activate Raf and PI-3 kinases, as well as exchange factors for RalA and RalB GTPases. Many previous studies have reported that the Ral-signaling cascade contributes positively to Ras-mediated oncogenesis. Here, using a bioengineered tissue model of early steps in Ras-induced human squamous cell carcinoma of the skin, we found the opposite. Conversion of Ras-expressing keratinocytes from a premalignant to malignant state induced by decreasing E-cadherin function was associated with and required an approximately two to threefold decrease in RalA expression. Moreover, direct knockdown of RalA to a similar degree by shRNA expression in these cells reduced E-cadherin levels and also induced progression to a malignant phenotype. Knockdown of the Ral effector, Exo84, mimicked the effects of decreasing RalA levels in these engineered tissues. These phenomena can be explained by our finding that the stability of E-cadherin in Ras-expressing keratinocytes depends upon this RalA signaling cascade. These results imply that an important component of the early stages in squamous carcinoma progression may be a modest decrease in RalA gene expression that magnifies the effects of decreased E-cadherin expression by promoting its degradation.

Show MeSH
Related in: MedlinePlus