IGFBP5 and pulmonary fibrosis: Lung fibrosis. EGR1 is involved in lung fibrosis downstream of IGFBP-5 (insulin-like growth factor (IGF) binding protein-5) to promote fibrotic gene transcription [145] and downstream of TGFβ1 to activate the transcription of the hyaluronan receptor CD44V6 (CD44 containing variable exon 6 (v6)) expression in lung fibroblasts in the context of idiopathic pulmonary fibrosis [146].