Recent research has identified that METTL1 is upregulated in cutaneous squamous cell carcinoma (cSCC) and plays an oncogenic role. In vitro experiments revealed that inhibiting METTL1 significantly reduced the survival, migration, and invasion of cSCC cell lines HSC-1 and A431. Additionally, METTL1 knockdown diminished cSCC tumorigenesis in nude mice. Mechanistically, METTL1 mediates the m7G modification of ATF4 mRNA, enhancing its stability and expression through methyltransferase activity. A positive correlation between ATF4 and METTL1 was observed in cSCC tumor tissues. Overexpression of ATF4 reversed the anti-tumor effects of METTL1 knockdown, indicating METTL1's oncogenic role and m7G modification mechanisms as potential therapeutic targets for cSCC.
In a detailed analysis of METTL1 expression, immunohistochemistry (IHC) was performed on paraffin-embedded sections from 36 cSCC and 7 normal specimens, showing significantly elevated METTL1 levels in tumor tissues compared to normal skin. Further assessments using qRT-PCR indicated consistent increases in METTL1 mRNA levels in cSCC tissues versus normal controls. The study also evaluated METTL1's involvement in tumor progression by comparing its protein and mRNA levels in cSCC cell lines (HSC-1 and A431) with control HaCaT keratinocytes, revealing marked upregulation in cSCC cells.
To explore METTL1's role in cSCC cell progression, stable METTL1 knockdown HSC-1 and A431 cell lines were created using shRNA. Successful knockdown was confirmed via reduced METTL1 mRNA and protein levels, accompanied by decreased m7G methylation. Subsequent assays demonstrated that METTL1 knockdown led to reduced cell viability, proliferation, and increased apoptosis in cSCC cells.
In vivo studies using a xenograft tumor model showed that tumors from METTL1-knockdown cells had significantly lower growth rates and weights compared to controls. RNA-seq analyses revealed that METTL1 knockdown resulted in the downregulation of 4017 genes, including key glycolytic metabolism-related genes. Notably, ATF4 mRNA was identified as a target for m7G modification by METTL1, with experiments confirming its enhanced stability and expression dependent on METTL1's activity.
These findings collectively underscore METTL1's critical role in promoting cSCC cell survival and proliferation through ATF4-mediated mechanisms, suggesting its potential as a therapeutic target in cSCC treatment strategies.