Identification of Phosphotyrosine-Mutant Desmin in Human Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), a deadly cancer with a 5-year survival rate of ∼12%, is characterized by frequently mutated KRAS, early metastasis, and extensive desmoplasia. The latter, a formation of dense fibrotic tissue generated by pancreatic stellar cells (PSC) and tumor cells, makes up to 80% of the tumor mass and leads to treatment failure. To search for novel protein biomarkers for actionable tyrosine kinases, we used a combination of two orthogonal protein analysis methods, western blotting (WB) and mass spectrometry (MS). That is, we used 1D/2D phosphotyrosine (pTyr) WB in combination with nano liquid chromatography tandem mass spectrometry (NanoLC-MS/MS) to analyze homogenates of 6 PDAC tumor samples and 5 normal adjacent tissue controls. Surprisingly, we found a novel, abundant 55 kDa pTyr-protein in 2/6 tumor samples and identified it as mutated pTyr-desmin. Further proteomics analysis of the purified protein cut from multiple Coomassie-stained 2D gels revealed that the mutant amino acid, tyrosine (D399Y), is phosphorylated (pTyr). A possible role for mutant pTyr-desmin in PDAC metastasis is discussed, along with peptide inhibitor drugs.