Background: p63, a member of the p53 gene family, is an important regulator for epithelial tissue growth and development. ∆Np63α is the main isoform of p63 and highly expressed in Non-melanoma skin cancer (NMSC). Extracellular signal-regulated kinase 3 (ERK3) is an atypical mitogen-activated protein kinase (MAPK) whose biochemical features and cellular regulation are distinct from those of conventional MAPKs such as ERK1/2. While ERK3 has been shown to be upregulated in lung cancers and head and neck cancers, in which it promotes cancer cell migration and invasion, little is known about the implication of ERK3 in NMSCs.
Methods: Fluorescent immunohistochemistry was performed to evaluate the expression levels of DNp63a and ERK3 in normal and NMSC specimens. Dunnett’s test was performed to compare mean fluorescence intensity (MFI, indicator of expression levels) of p63 or ERK3 between normal cutaneous samples and NMSC samples (i.e., Actinic Keratosis (AK), a precursor to invasive squamous cell carcinoma, squamous cell carcinoma (SCC), and basal cell carcinoma (BCC)). A mixed effects (ANOVA) test was used to determine the correlation between DNp63a and ERK3 expression levels (MFI). The regulation of ERK3 by DNp63a was studied by qRT-PCR, Western blot and luciferase assay. The effect of ERK3 regulation by DNp63a on cell migration was measured by performing trans-well migration assay.
Results: The expression levels of both ∆Np63α and ERK3 proteins are upregulated in NMSCs compared to normal tissues. There is a strong positive correlation between ∆Np63α and ERK3 expression in normal skin and patients with AK, SCC and BCC. Further, we found that ∆Np63α positively regulates ERK3 transcript and protein levels in A431 and HaCaT skin cells, underlying the upregulation of ERK3 expression and its positive correlation with ∆Np63α in NMSCs. Moreover, similar to the effect of ∆Np63α depletion, silencing ERK3 greatly enhanced A431 cell migration. Restoration of ERK3 expression under the condition of silencing ∆Np63α counteracted the increase in cell migration induced by the depletion of ∆Np63α.
Conclusions: ERK3 is positively regulated by ∆Np63α and mediates the role of ∆Np63α in suppressing cell migration in NMSC.