Pervanadate-mediated tyrosine phosphorylation of keratins 8 and 19 via a p38 mitogen-activated protein kinase-dependent pathway

Glandular epithelia express the keratin intermediate filament (IF) polypept ides 8, 18 and 19 (K8/18/19). These proteins undergo significant serine pho sphorylation upon stimulation with growth factors and during mitosis, with subsequent modulation of their organization and interaction with associated proteins. Here we demonstrate reversible and dynamic tyrosine phosphorylat ion of K8 and K19, but not K18, upon exposure of intact mouse colon or cult ured human cells to pervanadate. K8/19 tyrosine phosphorylation was confirm ed by metabolic (PO4)-P-32-labeling followed by phosphoamino acid analysis, and by immunoblotting with anti-phosphotyrosine antibodies. Pervanadate tr eatment increases keratin solubility and also indirectly increases K8/18 se rine phosphorylation at several known sites, some of which were previously shown to be associated with EGF stimulation, extracellular signal-regulated kinase (ERK), or p38 kinase activation, However, K8/19 tyrosine phosphoryl ation is independent of EGF signaling or ERK activation while inhibition of p38 kinase activity blocks pervanadate-induced K8/19 tyrosine phosphorylat ion, Our results demonstrate tyrosine phosphatase inhibitor-mediated in viv o tyrosine phosphorylation of K8/19, but not K18, and suggest that tyrosine phosphorylation may be a general modification of other IF proteins. K8/19 tyrosine phosphorylation involves a pathway that utilizes the p38 mitogen-a ctivated protein kinase, but appears independent of EGF signaling or ERK ki nase activation.