Areca (betel) was recently proved a carcinogenic substance by the International Agency for Research on Cancer. However, the signaling impact of areca in oral keratinocyte is still obscure. Mitogen‐activated protein kinase superfamilies, including extracellular signal‐regulated kinase (ERK), c‐Jun N‐terminal kinases (JNK) and p38, together with transcription factor NF‐κB, are important signaling elements. We examined the activation of these signaling pathways in OECM‐1 and SAS oral keratinocytes, treated with ripe areca nut extract (ANE). In both cells, a rapid increase in JNK1 activity at 0.5 hr was noted following treatment of ANE. ERK was profoundly activated during 0.5–2 hr in OECM‐1 cells. Contrasting p38 activity was noted in these 2 cells. In both cells, ANE also activated NF‐κB pathway in a biphasic manner, particularly for SAS cells. NF‐κB was activated by ∼ 2‐ to 4‐fold at 0.5–1 hr and a plateau or slight decrease of activity existed between 1 and 6 hr. Later, another higher episode of NF‐κB activity was raised. This was accompanied with the rapid degradation in cytosolic IκBα as well as an increase of nuclear NF‐κB in both cells. ANE treatment did not activate epidermal growth factor receptor signaling system, but blockage of NF‐κB activation rendered the suppression of ANE‐modulated COX‐2 upregulation in OECM‐1. This study identified that ANE affected interactive signaling systems in oral keratonocytes that could be the pathogenetic basis for areca. © 2005 Wiley‐Liss, Inc.

OC3 cell line could be valuable in understanding the genetic impairments and phenotypic changes associated with areca in oral keratinocyte.

To identify molecular events involved in the pathogenesis of oral squamous cell carcinoma (OSCC), genes differentially expressed in OSCC and non-cancerous matched tissue (NCMT) samples were analysed using a subtractive hybridization strategy. NCMT-enriching clones that have been linked to suppressor pathway in previous studies were subjected to advanced analyses. Complete absence of insulin-like growth factor binding protein-5 (IGFBP-5) expression at both the mRNA and the protein level was identified in nearly all (5/6) OSCC cell lines with the exception of the SCC25 cell line, which exhibited high IGFBP-5 expression. However, this protein is consistently present in cultured normal human oral keratinocytes (NHOKs). Immunohistochemistry revealed moderate to strong cytoplasmic immunoreactivity of IGFBP-5 in the stratum spinosum and stratum granulosum in the vast majority of NCMT samples. A remarkable reduction in IGFBP-5 immunoreactivity was detected in 56% (26/46) of OSCC samples, compared with the corresponding NCMT (p < 0.0001). Induction of differentiation in both NHOKs and SCC25 up-regulated IGFBP-5 expression. Administration of a green tea compound with anti-cancer properties, (-)-epigallocatechin 3-gallate, at a concentration of 5-20 micro g/ml also up-regulated IGFBP-5 expression in NHOKs in a dose-dependent manner. The findings suggest that IGFBP-5 may be an important factor in the differentiation of oral keratinocytes and that down-regulation of IGFBP-5 may be involved in the neoplastic transformation of oral keratinocytes.

This study established a novel toxicogenomic database for rANE. The down-regulation of KGF-1 expression in oral fibroblast cell lines potentially impairs the proliferation of overlying keratinocytes, which could partially explain the frequent epithelial atrophy observed in chronic areca chewers in vivo.

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