Fig. 9. Schematic of K8 phosphorylation changes in response to osmotic alterations. K8 (and all other IF proteins) consist of a central, relatively conserved, coiled-coil -helical `rod' domain that is flanked by non--helical relatively non-conserved `head' and `tail' domains (Herrmann and Aebi, 2004). The head and tail domains contain most of the known posttranslational modification of IF proteins (Coulombe and Omary, 2002; Omary et al., 2004). Hyperosmotic stress results in human K8 hyperphosphorylation (upward-pointing double arrows) at Ser73 and Ser431. Hyposmotic stress (downward-pointing double arrows) also induces K8 hyperphosphorylation at Ser73 and Ser431 except in the case of HT29 cells where it induces K8 dephosphorylation via PP2A.