Proline- and alanine-rich Ste20-related kinase associates with F-actin andtranslocates from the cytosol to cytoskeleton upon cellular stresses

Proline- and alanine-rich Ste20-related kinase (PASK) is a Ste20-related pr otein kinase isolated from rat brain. Cell fractionation studies showed tha t PASK was present both in the cytosol and in Triton X-100-insoluble cytosk eletal fraction in rat tissues. In brain, PASK associated with protein comp lexes that contained actin and tubulin, confirming the association of PASK with the cytoskeleton in vivo. Glutathione S-transferase-PASK fusion protei n cosedimented with F-actin, indicating that PASK binds to F-actin, In cont rast to rat tissues, PASK was detected only in the Triton X-100-soluble cyt osolic fraction in cultured PC12 and NIR 3T3 cells. Cytosolic PASK transloc ated to the cytoskeleton when these cells were stimulated with severe cellu lar stresses such as hypertonic sodium chloride, hydrogen peroxide, and hea t shock at 45 degrees C, Our results suggest that PASK may be involved in t he regulation of the cytoskeleton in response to cellular stresses such as hyperosmotic shock.