Cyclic AMP-Dependent Protein Kinase Isoenzymes in Human Myeloid Leukemia (HL60) and Breast Tumor (MCF-7) Cells

Combinations of retinoic acid (RA) and cAMP mediate many biological responses in a large variety of cell types. While the basis for the apparent synergistic effects of RA and cAMP are not clearly defined, it is likely that activation of PKA by cAMP is involved. However, literature reports concerning the identity of PKA isoforms in HL60 and MCF-7 cells are conflicting. The purpose of the present investigation is to identify PKA isoforms in HL60 and MCF-7 cells. Utilization of high-performance anion-exchange liquid chromatography, immunoblotting, and 8-azido-cAMP photoaffinity binding resulted in the finding that HL60 cells contain PKA types Iα and IIα, while MCF-7 cells contain PKA types Iα, IIα, and IIβ. PKA type Iα in both HL60 and MCF-7 cells eluted from columns as two well-separated peaks. One peak eluted at a low salt concentration in agreement with previous reports. The second HL60 PKA type Iα peak eluted at a salt concentration intermediate between that eluting the first peak and that eluting PKA type IIα and contained approximately 62% of the total RIα protein. However, the second MCF-7 PKA type Iα peak contained approximately 66% of the total RIα protein and co-eluted with PKA types IIα and IIβ. This “contamination” of PKA type II fractions with PKA type I has led, in some cases, to interpretations that may need reevaluation.