Inhibition of phorbol ester-induced AP-1-DNA binding, c-Jun protein and c-jun mRNA by dietary energy restriction is reversed by adrenalectomy in SENCAR mouse epidermis

Weight control by exercise and dietary calorie restriction (DCR) has been associated with reduced cancer risk, but the underlying mechanisms are not well understood. This study was designed to compare the effects of weight loss by increasing physical activity or decreasing calorie intake on tumor promoter-induced Ras-MAPK and PI3K-Akt pathways. SENCAR mice were randomly assigned to one of the following five groups: ad libitum-fed sedentary control, ad libitum-fed exercise (AL؉Exe), exercise but pair-fed at the amount as controls (PF؉Exe), 20% DCR, and 20% DCR plus exercise (DCR؉Exe). After 10 weeks, body weight and body fat significantly decreased in the groups of DCR, DCR؉Exe, and PF؉Exe when compared with the controls. AL؉Exe did not induce weight loss due to, at least in part, increased food intake. Plasma IGF-1 levels reduced significantly in DCR and DCR؉Exe but not PF؉Exe. The protein H-Ras and activated Ras-GTP significantly decreased in TPA-induced skin tissues of DCR-fed mice but not exercised mice. PI3K protein, phosphoserine Akt, and p42/p44-MAPK were reduced, however, in both DCR and PF؉Exe groups. Immunohistochemistry demonstrated that the significantly reduced H-Ras occurred in subcutaneous fat cells, while the reduced PI3K and PCNA took place only in the epidermis. Plasma leptin decreased in PF؉Exe, DCR, and DCR؉Exe, while the caspase-3 activity increased in DCR؉Exe only. Genomic microarray analysis further indicated that the expression of 34 genes relevant to PI3K and 31 genes to the MAPK pathway were significantly regulated by either DCR or PF؉Exe treatments. The reduced PI3K in PF؉Exe mice was partially reversed by IGF-1 treatment. The overall results of this study demonstrated that DCR abrogated both Ras and PI3K signaling, which might inhibit TPA-induced proliferation and anti-apoptosis. Selective inhibition of PI3K by PF؉Exe but not AL؉Exe seems more attributable to the magnitude of the caloric deficit and/or body fat loss than diet versus exercise comparison.The National Health and Nutrition Examination Survey indicates growing rates of obesity in American adults and overweight children over the past 20 years (1). Numerous prospective and case-control studies associated with weight control and physical activity estimate that excess body weight and sedentary life style account for about 39% endometrial, 25% kidney, 11% colon, 9% postmenopausal breast cancer, and 5% total cancer incidence (2-3). It has been suggested that those 25% over normal weight have a 33% greater cancer risk than those who maintain ideal body weight (4). Therefore, for many individuals, it would be advisable to maintain weight within the normal range to reduce their risk of cancer.Overweight/obesity is recognized as a reflection of a positive energy state that results from either over-consumption of energy or low energy expenditure. There is ample evidence that weight control via decreasing calorie intake and/or increasing physical activity reduces cancer risk in animal models. For almost a century, dietary calorie restr...

Section: Accession Numbersupporting

confidence: 51%

“…Activated GTP-bound Ras further initiates the MAPK cascade. Previous studies demonstrated that DCR treatment inhibited TPA-promoted skin carcinogenesis by reducing certain isoforms of PKC (32) down to the ERK pathway (33), and then repressing transcriptional regulation of AP-1 (34).…”

mentioning

confidence: 99%

Effects of Dietary Calorie Restriction or Exercise on the PI3K and Ras Signaling Pathways in the Skin of Mice

Xie

Jiang

Ouyang

et al. 2007

“…Because TPA is a well known AP1 activator (15,16), we examined the effects of TPA on BCSG1 promoter activity. Treatment of cells with TPA for 24 h stimulated the BCSG1 promoter activity 3.1-fold in SKBR-3 cells, 2.3-fold in T47D, and 4.9-fold in HepG2 cells.…”

Section: Resultsmentioning

confidence: 99%

Blockade of AP1 Transactivation Abrogates the Abnormal Expression of Breast Cancer-specific Gene 1 in Breast Cancer Cells

Lü

Zhang

Gupta

et al. 2002

Breast cancer-specific gene 1 (BCSG1) is not expressed in normal breast tissue but is highly expressed in the vast majority of invasive and metastatic breast carcinomas. When over-expressed, BCSG1 significantly stimulates the proliferation and invasion of breast cancer cells. The accumulated evidence suggests that the aberrant expression of BCSG1 in breast carcinomas is caused by transcriptional activation of the BCSG1 gene. However, the transcription factors that activate BCSG1 transcription have not been identified. In this study, we extensively investigated the role of AP1 in BCSG1 expression in breast cancer cells. We demonstrate that there are two closely located AP1 binding sites residing in the first intron of the BCSG1 gene. Mutation of either AP1 motif on the BCSG1 promoter constructs markedly reduces the promoter activity. We further show that 12-O-tetradecanoylphorbol-13-acetate (TPA) increases BCSG1 mRNA expression and up-regulates BCSG1 promoter activity through the intronic AP1 sites. The effect of TPA on BCSG1 transcription is also demonstrated under in vivo conditions in intact cells by using chromatin immunoprecipitation assays that show the TPA-induced binding of c-Jun to the chromatin region encompassing the intronic AP1 sites. Finally, to examine the direct effect of AP1 transactivation on BCSG1 expression, we established stable cell lines of T47D that express the dominant negative mutant of c-Jun, TAM67. RT-PCR and Western blot analyses demonstrated that levels of BCSG1 mRNA and protein in TAM67 transfectants were drastically reduced as compared with mocktransfected cells. Furthermore, inhibition of BCSG1 expression by blocking AP1 transactivation produced a similar repressive effect on cell growth as that by expressing BCSG1 antisense mRNA. We show that the anchorage-independent growth of T47D cells expressing either TAM67 or BCSG1 antisense mRNA is significantly inhibited. Taken together, we provide strong evidence that AP1 plays an overriding role in the transcription of the BCSG1 gene and that blockade of AP1 transactivation down-regulates BCSG1 expression and suppresses tumor phenotype.Previous studies conducted by differential DNA sequencing and in situ hybridization have identified BCSG1 1 (1), also referred to as synuclein ␥ (2) or persyn (3), as a breast cancerspecific gene because of its distinct expression pattern in breast tissues. BCSG1 is not expressed in normal breast tissue or tissues with benign breast diseases but is highly expressed in the vast majority of stage III/IV breast carcinomas (1, 4). BCSG1 expression in advanced breast carcinomas is not merely adventitious but plays a positive role in the process of invasion and metastasis. It has been demonstrated that exogenous expression of BCSG1 in breast cancer cells leads to a significant increase in cell motility and cell proliferation in cell culture (5, 6), as well as a profound augmentation of metastasis in nude mice (5). Thus far, BCSG1 gene mutations or amplifications have not been found by examination of breast carc...

“…Further studies are needed to elucidate whether the binding of SIRT1 to bZIP domain of c-Fos and c-Jun participates in AP-1 transcriptional regulation in a deacetylase-independent manner. CR decreases AP-1 DNA binding in mouse epidermis (43) and attenuates the aging-related AP-1 activation (23,44). Numerous studies have linked the beneficial effects of mammalian CR with increased cellular SIRT1 expression (18,26).…”

Section: Sirt1 Is a Nadmentioning

confidence: 99%

SIRT1 Suppresses Activator Protein-1 Transcriptional Activity and Cyclooxygenase-2 Expression in Macrophages

Zhang¹,

Chen²,

Liu

et al. 2010

188

132

SIRT1 (Sirtuin type 1), a mammalian orthologue of yeast SIR2 (silent information regulator 2), has been shown to mediate a variety of calorie restriction (CR)-induced physiological events, such as cell fate regulation via deacetylation of the substrate proteins. However, whether SIRT1 deacetylates activator protein-1 (AP-1) to influence its transcriptional activity and target gene expression is still unknown. Here we demonstrate that SIRT1 directly interacts with the basic leucine zipper domains of c-Fos and c-Jun, the major components of AP-1, by which SIRT1 suppressed the transcriptional activity of AP-1. This process requires the deacetylase activity of SIRT1. Notably, SIRT1 reduced the expression of COX-2, a typical AP-1 target gene, and decreased prostaglandin E 2 (PGE 2 ) production of peritoneal macrophages (pM⌽s). pM⌽s with SIRT1 overexpression displayed improved phagocytosis and tumoricidal functions, which are associated with depressed PGE 2 . Furthermore, SIRT1 protein level was up-regulated in CR mouse pM⌽s, whereas elevated SIRT1 decreased COX-2 expression and improved PGE 2 -related macrophage functions that were reversed following inhibition of SIRT1 deacetylase activity. Thus, our results indicate that SIRT1 may be a mediator of CR-induced macrophage regulation, and its deacetylase activity contributes to the inhibition of AP-1 transcriptional activity and COX-2 expression leading to amelioration of macrophage function.