cAMP-dependent protein kinases I and II: divergent turnover of subunits

Abstract

cAMP-dependent protein kinase subunits were isolated from livers of rats that had been subjected to biosynthetic labeling with radioactive leucine. By application of ligand and antibody affinity techniques pure regulatory (R I; R II) and catalytic (C) subunits could be obtained in high yields, which allowed measurement of the apparent degradation rate constants and half-lives following a double isotope labeling protocol. In this way marked differences of apparent half-lives of regulatory subunits R I (t1/2 = 31 h) and R II (t1/2 = 125 h) were observed. To avoid the negative influence of reutilization inherent in the decay experiments, specific radioactivities were determined after a short isotope pulse. This parameter, which under steady-state conditions reflects the fractional turnover rate of the subunits, was found to be different for all three protein kinase subunits. Relative to total liver protein, the ratios R I:R II:C corresponded to 3.9:0.6:2. Our data indicate that in each type of protein kinase isoenzymes regulatory and catalytic subunits turn over with similar rates. The type I isoenzyme, however, is renewed much faster than protein kinase II. Furthermore, our findings are consistent with the thesis that free subunits as generated by activation are more susceptible to degradation than the holoenzymes, leading under steady-state conditions to compensatory resynthesis. Since renewal of R I exceeded that of R II also in two other tissues, the elevated turnover of protein kinase I as an indicator of preferential activation appears to be a general phenomenon. The different turnover of the two isoenzymes, then, may relate to different cellular functions like modulation of enzyme activity vs. modulation of gene activity.

Activation of Pedunculopontine Tegmental Protein Kinase A: A Mechanism for Rapid Eye Movement Sleep Generation in the Freely Moving Rat

“…A simultaneous increase in levels of C subunits and decrease in levels of R subunits indicates that the active form of intracellular PKA is increased (Weber and Hilz, 1986;Meinkoth et al, 1990;Spaulding, 1993). Thus, the Figure 8.…”

“…During low REM sleep, levels of C subunit expression increased, whereas levels of RII␣ and RII␤ subunits decreased. These results suggest that availability of the active form of PKA is reduced in the mPRF during REM sleep (Weber and Hilz, 1986;Meinkoth et al, 1990;Spaulding, 1993). Because no other studies have measured sleep-dependent PKA subunit expression in the brain, these results could not be compared.…”

“…Thus, increased expression of C subunits is an indication that there is an increased demand for PKA activity to activate genes and ultimately to produce a behavioral response specific to that particular cell (Meinkoth et al, 1990). In contrast, additional R subunits would bind with free C subunits and ultimately reduce the activity of PKA activation-mediated cellular and behavioral response (Weber and Hilz, 1986;Spaulding, 1993).…”

Pairs of cyclic AMP analogs, that are specifically synergistic for type I and type II cAMP‐dependent protein kinases, mimic thyrotropin effects on the function, differentiation expression and mitogenesis of dog thyroid cells

“…Bt6cAMP, N6-butyryladenosine 3',5'-phosphate; Bz6cAMP, N6-benzoyladenosine 3',5'-phosphate; AHxA'cAMP, 8-(6-aminohexyl)aminoadenosine 3',5'-phosphate; SMe'cAMP, 8-thiomethyladenosine 3',5'-phosphate; Bt2cAMP, N6,2'-0-dibutyryladenosine 3',5'-phosphate; cAMP [S], adenosine 3',5'-monophosphorothioate with the sulphur atom in the axial position; N:cAMP, 8-azidoadenosine 3',5'-phosphate; iPrS'cAMP, S-thioisopropyladenosine 3',5'-phosphate; CIPhS'cAMP, 8-thioparachlorophenyladenosine 3',5'-phosphate; PKA, CAMP-dependent protein kinases; PKI and PKII, CAMP-dependent protein kinase types I and 11, respectively; RI and RII, regulatory subunits of CAMP-dependent protein kinase types I and 11, respectively. of the two types during cell cycles [6,71; different turnover of the two enzymes [8]; selective activation of one isozyme by hormone in some cells [9 -111; decreased levels of one of the two isozymes associated with psoriasis [12], leukemia [13], or a neoplastic glioma cell line [14]. Thus, the major aspects of cell life, i. e. acute activation, growth, differentiation and disease, have been related to transient or sustained changes in the protein kinase pattern.…”

The v-Ki-Ras Oncogene Alters cAMP Nuclear Signaling by Regulating the Location and the Expression of cAMP-dependent Protein Kinase IIβ

“…R subunits are differentially expressed in neuronal and neuroendocrine cells (24). RI has a higher affinity for cAMP than RII␣ and RII␤ (25,26) and also turns over more rapidly (27). The RII subunits in the PKAII holoenzyme are phosphorylated by the catalytic subunit (25).…”