Cold-Stimulated Increase in a Regulatory Subunit of cAMP-Dependent Protein Kinase in Human Hepatoblastoma Cells
AbstractAlthough cold-stress responses in bacteria and plants have been well studied and hypothermic conditions are used in clinical treatments, there has been little investigation of cold-stress responses in human cells, and there has been no report on the involvement of signal transduction modulators in the cold-stress response in human cells. We therefore investigated alterations in the expression of genes involved in the signal transduction system and the mechanisms of cold-stimulated increases in the expression of genes in human hepatoblastoma (HepG2) cells. Using a cDNA expression array method, we found that a transcript encoding a regulatory subunit I β (RI β ) of cyclic AMP-dependent protein kinase (PKA) was increased in cold-stressed cells. Western blot analysis revealed that the amount of PKA RI β protein was increased by cold treatment, while that of a PKA catalytic subunit (C) was unchanged. The protein level of PKA RI β was increased in cells treated with low concentrations of actinomycin D, whereas that of PKA C was not, implying that the increase was caused by the suppression of transcription at low temperatures. In addition, degradation of the PKA RI β protein was not stimulated by cold treatment, unlike that of the PKA C protein. The results suggest that signal transduction through PKA also participates in cold-stress responses in human cells and that multiple mechanisms are involved in the increase in the level of the PKA RI β protein.