Carcinogenesis is a multistep process wherein cells accumulate multiple genetic alterations and progress to a more malignant phenotype. It has been proposed that sequential accumulation of gene abnormalities in specific genes drives the transition from non-tumorous epithelia through a preneoplastic lesion/benign
tumor to
cancer. Histologically,
oral squamous cell carcinoma (OSCC) progresses in multiple ordered steps that begin with mucosal epithelial cell
hyperplasia, which is followed by dysplasia,
carcinoma in situ and invasive
carcinoma. It is therefore hypothesized that genetic alteration-mediated multistep
carcinogenesis would be involved in the development of OSCC; however, the detailed molecular mechanisms are unknown. We clarified the comprehensive gene expression patterns and carried out an enrichment analysis using
DNA microarray data from a pathological specimen of OSCC (including a non-
tumor region,
carcinoma in situ lesion and invasive
carcinoma lesion). The expression of numerous genes and signal activation were altered in the development of OSCC. Among these, the p63 expression was increased and the
MEK/ERK-MAPK pathway was activated in
carcinoma in situ lesion and in invasive
carcinoma lesion. Immunohistochemical analyses revealed that p63 was initially upregulated in
carcinoma in situ and ERK was sequentially activated in invasive
carcinoma lesions in OSCC specimens.
ADP-ribosylation factor (ARF)-like 4c (ARL4C), the expression of which is reportedly induced by p63 and/or the
MEK/ERK-MAPK pathway in OSCC cells, has been shown to promote
tumorigenesis. Immunohistochemically, in OSCC specimens, ARL4C was more frequently detected in
tumor lesions, especially in invasive
carcinoma lesions, than in
carcinoma in situ lesions. Additionally, ARL4C and phosphorylated ERK were frequently merged in invasive
carcinoma lesions. Loss-of-function experiments using inhibitors and siRNAs revealed that p63 and
MEK/ERK-MAPK cooperatively induce the expression of ARL4C and cell growth in OSCC cells. These results suggest that the stepwise activation of p63 and
MEK/ERK-MAPK contributes to OSCC
tumor cell growth through regulation of ARL4C expression.