EGF-mediated signaling Cisplatin FDA pathways are also known to play important roles in the organization of TJs, in which they regulate the expression and localization of claudin proteins. For instance, EGF was reported to induce the upregulation of claudins 1, 3 and 4, and the EGF-induced downregulation of claudin-2 increases the force of the intercellular barrier, as determined by an increased transepithelial electrical resistance (TER) in MDCK-II cells [14], [15]. However, using the same model (MDCK cells), other authors have reported that the downregulation of claudin-2 induced higher cell motility, even with increased TER [16]. Recently, the EGFR/ERK/c-Fos pathway was shown to up-regulate claudin-2, an increase that was correlated with increased intercellular permeability and cell migration in human lung adenocarcinoma cells [17], [18].
Little information is known about the molecular mechanisms underlying the alterations in claudin expression that are associated with colorectal tumorigenesis. We have shown that patients with colorectal cancer presented increased expression levels of claudins 1, 3 and 4, which altered the barrier function of TJs [19]. Recent studies have reported a controversial role for claudin-1 during colorectal carcinogenesis; increased claudin-1 expression was observed in hepatic metastatic lesions of colorectal cancer, but this expression was decreased in the lymph node metastases of colon carcinomas [20], [21]. Additionally, the ERK1/2 and PI3K pathways have been reported to mediate increases in EGF-induced claudin-2 expression in colon cancer cells; this event was accompanied by increases in proliferation, anchorage-independent growth and tumor growth in vivo [22].
Therefore, it is important to understand the molecular mechanisms that regulate the expression of other claudin family members and the implications of claudin overexpression in colorectal cancer progression. In the present study, we show that the EGF-mediated increased expression of claudin-3 is related to increased cell migration and the formation of anchorage-dependent and anchorage-independent colonies in human colorectal adenocarcinoma HT-29 cells. Furthermore, we show that these events were mediated by the ERK1/2 and PI3K-Akt pathways. We also demonstrated that the forced overexpression of claudin-3 in HT-29 cells by genetic manipulation increased the malignant potential, while the overexpression of claudin-1 decreased cell migration.
Most importantly, our results reveal that claudin-3 plays a role as tumor promoter when its expression is imbalanced and implicate the ERK1/2 and PI3K-Akt signaling pathways as modulators of claudin-3 upregulation-related tumor progression in colorectal GSK-3 cancer cells. Materials and Methods Materials Anti-claudin-1 (Cat. no. 51�C9000) and anti-claudin-3 (Cat. no. 34�C1700) rabbit polyclonal antibodies as well as an anti-��-tubulin mouse monoclonal antibody (Cat. no.