Epithelial-to-mesenchymal transition (EMT) is a dynamic process and critically contributes
to treatment resistance, cancer cell dissemination and metastasis. Main objective
of this study was to investigate the functional interaction between Kallikrein-related
peptidase 6 (KLK6) and aldehyde dehydrogenase 1A (ALDH1A)-related retinoic acid (RA)
signaling as recent studies reported their impact on molecular features resembling
EMT in several malignancies, including head and neck squamous cell carcinoma (HNSCC).
In HNSCC cell lines, we demonstrate that KLK6 is not only a downstream target of ALDH1A-related
RA signaling, but also acts as an upstream regulator of ALDH1A3 expression. KLK6 and
ALDH1A3 co-expression was confirmed in a mouse xenograft model and two independent
HNSCC cohorts (HIPO-HNC and TCGA-HNC). KLK6 and ALDH1A3 co-expressed genes in HNSCC,
which are also differentially expression in HNSCC cells with silenced KLK6 expression
unraveled several subgroups of HNSCC patients with distinct histopathological and
clinical features. In summary, our study highlights a new functional circuit with
KLK6 and ALDH1A3 as key nodes and unraveled a gene expression signature, which predicts
unfavorable prognosis in human papilloma virus (HPV)-negative HNSCC.