The ERBB4 protein had similar expression pattern to that of DCLK1 and PDK4 proteins, and it was mainly expressed in the epithelial layer and smooth muscle cells of fibrotic lesions in IPF lungs and in the airway epithelium of control lungs (Fig. 2g, Additional file 2: Fig. S2). This evidence concerns the gene PDK4 and idiopathic pulmonary fibrosis.