Type I Keratin 17 Protein Is Phosphorylated on Serine 44 by p90 Ribosomal Protein S6 Kinase 1 in a Growth- and Stress-Dependent Fashion

The document reports that Keratin 17 (K17), a protein expressed in epithelial appendages and induced in the epidermis during injury, inflammation, and diseases like psoriasis and cancer, undergoes phosphorylation at serine 44 (Ser44) in response to growth stimuli and stress. This phosphorylation is mediated by p90 Ribosomal Protein S6 Kinase 1 (RSK1), a kinase involved in cell survival and proliferation. The phosphorylation of K17-Ser44 is rapid and transient, occurring in response to extracellular stimuli such as serum, EGF, phorbol ester, and stresses like hyperosmotic shock, UV irradiation, and oxidative stress, and is also present in basaloid skin tumors. The phosphorylated K17-Ser44 is mostly polymer-bound and does not significantly alter filament organization. These findings highlight the role of K17 in skin epithelium growth and stress responses, expanding the understanding of its regulation through post-translational modification.