PPAR␥ and C/EBP␣ are critical transcription factors in adipogenesis, but the precise role of these proteins has been difficult to ascertain because they positively regulate each other's expression. Questions remain about whether these factors operate independently in separate, parallel pathways of differentiation, or whether a single pathway exists. PPAR␥ can promote adipogenesis in C/EBP␣-deficient cells, but the converse has not been tested. We have created an immortalized line of fibroblasts lacking PPAR␥, which we use to show that C/EBP␣ has no ability to promote adipogenesis in the absence of PPAR␥. These results indicate that C/EBP␣ and PPAR␥ participate in a single pathway of fat cell development with PPAR␥ being the proximal effector of adipogenesis. Received September 27, 2001; revised version accepted November 9, 2001. Adipogenesis is the process by which undifferentiated precursor cells differentiate into fat cells. This has become one of the most intensively studied developmental processes for at least two reasons: the increasing prevalence of obesity in our society has focused attention on many aspects of fat cell biology, and the availability of good cell culture models of adipocyte differentiation has permitted detailed studies not possible in other systems. Experiments using these in vitro models of adipogenesis, which include the 3T3-L1 and 3T3-F442A lines, have illustrated the transcriptional cascade that promotes fat cell differentiation (Rosen et al. 2000). Representatives of several transcription factor families have been implicated in this process, including the CCAAT/enhancer binding proteins C/EBP␣, C/EBP␤, and C/EBP␦; the nuclear hormone receptor peroxisome proliferator-activated receptor ␥ (PPAR␥); and the basic helix-loop-helix protein ADD1/SREBP1c. Studies in adipogenic cell lines have shown that hormonal induction of differentiation is rapidly followed by expression of C/EBP␤ and C/EBP␦ (Cao et al. 1991;Yeh et al. 1995). Within the next day or so, levels of these proteins peak and then begin to drift downward, coincident with a rise in C/EBP␣ and PPAR␥. These latter factors induce gene expression changes characteristic of mature adipocytes and remain elevated for the life of the cell. In the present model of the transcriptional cascade leading to adipogenesis, C/EBP␤ and C/EBP␦ induce low levels of PPAR␥ and C/EBP␣, which are then able to induce each other's expression in a positive feedback loop that promotes and maintains the differentiated state. This model is consistent with gain-offunction data showing that the addition of either PPAR␥ or C/EBP␣ can promote adipogenesis in fibroblast cell lines (Lin and Lane 1994;Tontonoz et al. 1994).Loss-of-function studies have shown convincingly that PPAR␥ is required for adipogenesis in vivo and in vitro, and cells lacking PPAR␥ express greatly reduced levels of C/EBP␣ (Barak et al. 1999;Kubota et al. 1999;Rosen et al. 1999). Similarly, fibroblasts lacking C/EBP␣ have reduced adipogenic potential, and express reduced levels of PPAR␥ (Wu...

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This study developed and tested a structural model in examining the effects of mainland Chinese visitors' travel motivation, past experience, perceived constraint, and attitude on their intention of revisiting Hong Kong. Data were collected through telephone interviews ( n = 501) in Beijing and analyzed using structural equation modeling. Findings indicate that one of travel motivation's underlying dimensions, shopping, positively affected Beijing tourists' revisit intention to Hong Kong; past experience, as measured by the number of prior visits and satisfaction, also positively influenced revisit intention. Disinterest was the only constraint factor significantly negating revisit intention. In addition, attitude was found to play a significant mediating role in the total effect of satisfaction on revisit intention. Results suggest that in addition to further strengthening Hong Kong's “shopping paradise” image, destination marketers and managers should promote more novel features of local attractions and appeal to the relaxation need of repeat visitors.

OBJECTIVE-We identified lipocalin 2 (Lcn2) as a gene induced by dexamethasone and tumor necrosis factor-␣ in cultured adipocytes. The purpose of this study was to determine how expression of Lcn2 is regulated in fat cells and to ascertain whether Lcn2 could be involved in metabolic dysregulation associated with obesity. RESEARCH DESIGN AND METHODS-We examined Lcn2expression in murine tissues and in 3T3-L1 adipocytes in the presence and absence of various stimuli. We used quantitative Western blotting to observe Lcn2 serum levels in lean and obese mouse models. To assess effects on insulin action, we used retroviral delivery of short hairpin RNA to reduce Lcn2 levels in 3T3-L1 adipocytes.RESULTS-Lcn2 is highly expressed by fat cells in vivo and in vitro. Expression of Lcn2 is elevated by agents that promote insulin resistance and is reduced by thiazolidinediones. The expression of Lcn2 is induced during 3T3-L1 adipogenesis in a CCAAT/enhancer-binding protein-dependent manner. Lcn2 serum levels are elevated in multiple rodent models of obesity, and forced reduction of Lcn2 in 3T3-L1 adipocytes improves insulin action. Exogenous Lcn2 promotes insulin resistance in cultured hepatocytes. T he worldwide epidemic of obesity and type 2 diabetes has focused attention on adipocyte biology and the role of adipose tissue in the integration of systemic metabolism (1). The discovery of leptin more than a decade ago established a paradigm in which secreted proteins from adipocytes coordinate energy balance and glucose homeostasis (2,3). Since that initial discovery, the number of adipocytederived signaling molecules has grown ever larger, and the term adipokine was coined to reflect that many of these molecules exert positive or negative actions on inflammation. Several adipokines promote insulin sensitivity, including leptin (2), adiponectin (4), and visfatin (5), while others induce insulin resistance, such as resistin (6) and retinol binding protein (RBP)4 (7). CONCLUSIONS-Lcn2Lipocalin 2 (Lcn2)-also known as neutrophil gelatinase-associated lipocalin, siderocalin, and 24p3-is a member of a large superfamily of proteins that includes RBP4. Lipocalins are small generally secreted proteins with a hydrophobic ligand binding pocket (8). Known ligands for lipocalins include retinol, steroids, odorants, pheromones, and, in the case of Lcn2, siderophores (9). Siderophores are small molecules used by bacteria to poach iron from their hosts, a necessary cofactor for the growth of some pathogens. Lcn2 is used by the mammalian-innate immune system to sequester siderophore and thus deprive the bacteria of iron. Mice lacking Lcn2 appear normal but die when exposed to siderophorerequiring strains of bacteria in quantities that are cleared easily by wild-type mice (10,11). Lcn2 can thus be considered an iron transport protein, and it has been implicated in the apoptotic induction of pro-B-cells (12) and in the biology of the genitourinary system, both as a developmental factor and as a protective mechanism in renal ischemia (13).In this s...

This study focuses on the previsit stage of tourists by modeling the behavioral process incorporating expectation, motivation, and attitude in the context of Chinese outbound travelers. An expectation, motivation, and attitude (EMA) model is proposed based on a comprehensive literature review. An instrument is developed based on previous tourism and marketing studies as well as focus groups to measure the variables in the EMA model. Data are collected from 1,514 Beijing, Shanghai, and Guangzhou residents. Results of the study confirm the proposed relations that expectation of visiting an outbound destination has a direct effect on motivation to visit the destination; motivation has a direct effect on attitude toward visiting the destination; expectation of visiting the outbound destination has a direct effect on attitude toward visiting the destination; and motivation has a mediating effect on the relationship between expectation and attitude. Practical and theoretical contributions are discussed, with future research suggested.

Tourist behavior theories have been the focus of research in many tourism studies, but how travelers’ behavioral intention in choosing a travel destination is developed has rarely been investigated. This study tested the fit of the theory of planned behavior (TPB) with potential travelers from Mainland China to Hong Kong as the sample (n = 328). Results showed that data fitted the TPB model moderately well and explained respondents’traveling intention. Attitude, perceived behavioral control, and past behavior were found to be related to respondents’travel intention. Recommendations were provided for government and tourism bodies to market Hong Kong as a destination for Mainland Chinese travelers.

While the role of customer-to-customer (C2C) interaction in shaping service experience has been recognized in the services marketing literature, empirical examination of this issue is limited. Similarly, investigation of tourists’ social contacts has mainly focused on the tourist—local community and tourist—service personnel dyads, while much less is known about tourist-to-tourist interactions. To fill this knowledge gap, this study has examined interaction between tourists on cruise vacations and its impact on the cruise experience and vacation satisfaction. An online survey is conducted with an American online panel ( n = 613). The findings reveal that the quality of C2C interaction has positive direct impacts on the cruise experience as well as indirect effects on vacation satisfaction, mediated by cruise experience. Moreover, the quality of C2C interaction has suppressor effects on the quantity of C2C interaction. The results call for the incorporation of C2C interaction as one component of the relationship marketing theory.

The sufficiency of theory of planned behavior (TPB) is still being questioned although the model was validated in predicting a wide range of intentions and behaviors. Based on a comprehensive literature review, an extended TPB model of tourists was proposed to investigate relations among constructs of the model with the addition of motivation and actual behavior. An instrument was developed based on previous tourism and marketing studies as well as focus groups. A two-wave data collection was implemented, with data collected from 1,524 Beijing, Shanghai, and Guangzhou residents in Stage 1 and 311 respondents from the same cohort in Stage 2. Results of the study demonstrated that the extended TPB model with tourist motivation fit the data relatively well, explaining 5% more of the variation in behavioral intention in comparison with a base model without motivation. However, the model with both tourist motivation and actual behavior was not tenable, despite a marginal relationship found between behavioral intention and actual tourist behavior using regression analysis. The findings warrant further research examining the predictive power of behavioral intention on actual behavior.