PTBP1 and head and neck squamous cell carcinoma: However, because GRSF1 is mainly a mitochondrial RBP and is weakly expressed in epithelial cells (37) whereas PTBP1 is a well-defined alternative splicing regulator expressed in epithelial tissues, we chose to test whether experimental depletion of PTBP1 could enhance TP63 γ exon inclusion in a panel of HNSCC cell lines of different common tumor locations (FaDu, SCC9, SCC25, Detroit562, and A253).