EJB 85 0044 104 CAMP analogs, most of them modified in the adenine moiety, were tested as activators of CAMP-dependent protein kinase I (from rabbit or rat skeletal muscle) and kinase 11 (from bovine heart or rat skeletal muscle). When tested singly, only 2-phenyl-1 ,M-etheno-cAMP showed a considerably (sevenfold) higher potency as an activator of kinase 11 than of kinase I. Analogs containing an %amino modification preferentially activated kinase I, some being more than 10-fold more potent as activators of kinase I than kinase 11. When two analogs were combined, the concentration of one (complementary) analog required to halfmaximally activate each isozyme was determined in the presence of a fixed concentration of another (priming) analog. Analogs tested in combination had been analyzed for their affinity for the intrasubunit binding sites (A, B) of isozyme I and 11. The degree to which complementary analogs preferentially activated one isozyme was plotted against the mean site selectivity, i.e. (affinity A/B isozyme I. affinity A/B isozyme 11)' / 2. This plot produced a straight line, the slope of which reflected the ability of the priming analog to discriminate homologous sites on the isozymes. This means that the isozyme discriminating power of an analog pair can be quantitatively predicted from the affinity of the analogs for site A and B of the two enzymes. It also means that a systematic analysis of those features of analogs imparting a high mean site selectivity or the ability to discriminate between homologous isozyme sites will facilitate the synthesis of new even more isozyme-selective analogs. The pivotal role of CAMP-dependent protein kinase (cAK) as a mediator of CAMP action is well established [l-51. However, the biological significance of the presence of two distinct isozyme forms, cAKI and cAKI1 [6], is still largely unknown. Both isozymes contain one regulatory subunit (R) dimer and two catalytic (C) moieties [2-31. Each regulatory subunit has two types of binding sites for CAMP, termed A and B according to the rate with which they exchange bound labelled nucleotide [7-91. Activation of cAK by cAMP occurs according to the overall equation [lo]: RzCz + 4 CAMP + Rz CAMP)^ + 2 C. The free catalytic subunits transfer the terminal phosphate group of ATP to acceptor proteins, whose function thus may Correspondence to S. 0. Deskeland, Anatomisk Institutt, Universitetet i Bergen, Arstadveien 19, N-5000 Bergen, Norway Abbreviations. cAK1, cAKT1, CAMP-dependent protein kinase type I, 11; R', R", the regulatory subunit of cAKI, cAKII; C, the catalytic subunit of cAKI or cAKII; K,, apparent activation constant, i.e. the concentration of CAMP or an analog required for half-maximal kinase activation; KL, relative activation constant, i.e. K, CAMP/ K, analog; Kcom,,, the concentration of one (complementary) analog required to activate further, half-maximally, the kinase in the presence of a fixed level of another (priming) analog; Ksynr Ka/Kcomb. AI, AII, CAMP binding site type A of R' and R", respectively; BI...

Oxaliplatin combined with the bolus Nordic schedule of FU+FA (Nordic FLOX) is a well-tolerated, effective, and feasible bolus schedule as first-line treatment of metastatic colorectal cancer that yields comparable results compared with more complex schedules.

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Differential expression of type I and type II cAMP-dependent protein kinase isozymes has been linked to growth regulation and differentiation. We examined the expression of protein kinase isozymes in the LS 174T human colon cancer cell line during 8-chloroadenosine 3',5'-cyclic monophosphate (8-Cl-cAMP)-induced growth inhibition. Two species of R" (the regulatory subunit of protein kinase type II) with apparent Mr 52,000 (RI) and Mr 56,000 (RS) and a single species of R' (the regulatory subunit of protein kinase type I) with Mr 48,000 were identified in the cancer cells. R' and both forms of R" were covalently labeled with 8-azidoadenosine 3',5'-cyclic [32P]monophosphate, and two anti-R' antibodies that exclusively recognize either Rsl or Rs resolved two forms of the R" receptors. 8-Cl-cAMP treatment induced a decrease of R' and an increase of both Rs and R16 in the cytosols of cancer cells and rapid translocation (within 10 min) of R5 from the cytosol to nucleus. 8-Cl-cAMP caused transcriptional activation of the Rs receptor gene and inactivation of the R' receptor gene. It also exhibited high-affinity site-i-selective binding to the purified preparations of both R" receptor proteins. Thus, differential regulation of various forms of cAMP receptor proteins is involved in 8-Cl-cAMP-induced regulation of cancer cell growth, and nuclear translocation of Rs receptor protein appears to be an early event in such differential regulation.

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