Differential regulation of messenger ribonucleic acids for specific subunits of cyclic adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase by cAMP in rat Sertoli cells

cAMP-PKA signal transduction specificity in Saccharomyces cerevisiae

Living cells have developed a set of complex signaling responses, which allow them to withstand different environmental challenges. Signaling pathways enable the cell to monitor external and internal states and to articulate the appropriate physiological responses. Cellular signal transmission requires the dynamic formation of spatiotemporal controlled molecular interactions. One of the most important signaling circuits in Saccharomyces cerevisiae is the one controlled by cAMP-Protein Kinase A (PKA). In budding yeast, extracellular glucose and a plethora of signals related with growth and stress conditions regulate the intracellular cAMP levels that modulate PKA activity which in turn regulates a broad range of cellular processes. The cAMP-PKA signaling output requires a controlled specificity of the PKA responses. In this review we discuss the molecular mechanisms that are involved in the establishment of the specificity in the cAMP-PKA signaling pathway in S.cerevisiae.

Differential activations of PKC/PKA related to microvasculopathy in diabetic GK rats

Microvasculopathy is the most serious and predictable threat to the health of diabetic patients, which often results in end-stage renal disease, blindness, and limb amputations. Up to the present, the underlying mechanisms have remained elusive. Here, it was found that the differential activations of PKC/PKA were involved in diabetic microvasculopathy in diabetic GK rats. By real-time PCR, Western blot, immunohistochemistry, and enzyme activity assay, upregulation of PKC was prominent in kidney but was not significant in liver and brain. The expression and activity of PKA were lowered in kidney but comparable in brain and liver during diabetic nephropathy. Furthermore, the generation of reactive oxygen species, production of nitric oxide, and expression of inducible nitric oxide synthase induced by advanced glycation end products were inhibited by PKCβ inhibitor LY-333531 or a PKA agonist in rat glomerular microvascular endothelial cells. Finally, albuminuria was significantly lowered by a PKA agonist and boosted by a PKA antagonist. It suggested that the differential activations of PKC/PKA related to microvasculopathy in diabetes and that activation of PKA may protect the diabetic microvasculature.

Adenylyl cyclase-cyclicAMP signaling in mood disorders: role of the crucial phosphorylating enzyme protein kinase A

Mood disorders are among the most prevalent and recurrent forms of psychiatric illnesses. In the last decade, there has been increased understanding of the biological basis of mood disorders. In fact, novel mechanistic concepts of the neurobiology of unipolar and bipolar disorders are evolving based on recent pre-clinical and clinical studies, most of which now focus on the role of signal transduction mechanisms in these psychiatric illnesses. Particular investigative emphasis has been given to the role of phosphorylating enzymes, which are crucial in regulating gene expression and neuronal and synaptic plasticity. Among the most important phosphorylating enzyme is protein kinase A (PKA), a component of adenylyl cyclase-cyclic adenosine monophosphate (AC-cAMP) signaling system. In this review, we critically and comprehensively discuss the role of various components of AC-cAMP signaling in mood disorders, with a special focus on PKA, because of the interesting observation that have been made about its involvement in unipolar and bipolar disorders. We also discuss the functional significance of the findings regarding PKA by discussing the role of important PKA substrates, namely, Rap-1, cyclicAMP-response element binding protein, and brain-derived neurotrophic factor. These studies suggest the interesting possibility that PKA and related signaling molecules may serve as important neurobiological factors in mood disorders and may be relevant in target-specific therapeutic interventions for these disorders.

Expression of the cAMP-phosphodiesterase PDE4D isoforms and age-related changes in follicle-stimulating hormone-stimulated PDE4 activities in immature rat sertoli cells

Major changes in the cAMP-dependent signal transduction pathway triggered by FSH take place during transition of rat Sertoli cells from proliferative to the quiescent/terminally differentiated state. Using Sertoli cell cultures isolated from 10-, 20-, and 30-day-old rats, we recorded a specific increase in PDE4 activity in both the soluble and particulate subcellular fractions of 20-day-old Sertoli cells, which also displayed the highest cAMP response to FSH and the highest FSH-induced increase in PDE4 activity in both subcellular compartments. RT-PCR and immunoblotting experiments showed that almost all the PDE4D isoforms, known as the main cAMP-regulated rolipram-sensitive PDE in Sertoli cells, were expressed throughout the early postpartum period, whereas only the short PDE4D isoforms (PDE4D1 and PDE4D2) were transcriptionally regulated by FSH. Unexpectedly, the immunoblot data also revealed that the soluble PDE4 activities were mainly related to the long PDE4D isoforms and that short PDE4D1 was predominantly particulate. The subcellular distribution and expression of PDE4D proteins were unaffected by the developmental status of the Sertoli cells. Only the expression of short PDE4D1 appeared to be upregulated by FSH and only in 20-day-old Sertoli cells, which suggests phenotype-dependent differential regulation of Pde4d1 mRNA translation. Resensitization of the cAMP response to FSH in 20-day-old Sertoli cells was also associated with the highest FSH-induced transient increase in both soluble and particulate PDE4 activities, which suggests developmental changes in the PKA-mediated upregulation of the catalytic activities of long PDE4D. Such alterations may be involved in the phenotype-dependent alterations in FSH receptor coupling with its associated G proteins in rat Sertoli cells.

Cyclic AMP regulates the expression and nuclear translocation of RFC40 in MCF7 cells

We have previously shown that the regulatory subunit of PKA, RIalpha, functions as a nuclear transport protein for the second subunit of the replication factor C complex, RFC40, and that this transport appears to be crucial for cell cycle progression from G1 to S phase. In this study, we found that N(6)-monobutyryl cAMP significantly up-regulates the expression of RFC40 mRNA by 1.8-fold and its endogenous protein by 2.3-fold with a subsequent increase in the RIalpha-RFC40 complex formation by 3.2-fold. Additionally, the nuclear to cytoplasmic ratio of RFC40 increased by 26% followed by a parallel increase in the percentage of S phase cells by 33%. However, there was reduction in the percentage of G1 cells by 16% and G2/M cells by 43% with a concurrent accumulation of cells in S phase. Interestingly, the higher percentage of S phase cells did not correlate with a parallel increase in DNA replication. Moreover, although cAMP did not affect the expression of the other RFC subunits, there was a significant decrease in the RFC40-37 complex formation by 81.3%, substantiating the decrease in DNA replication rate. Taken together, these findings suggest that cAMP functions as an upstream modulator that regulates the expression and nuclear translocation of RFC40.

Brain region specific alterations in the protein and mRNA levels of protein kinase A subunits in the post-mortem brain of teenage suicide victims

Protein kinase A (PKA), a critical component of the adenylyl cyclase signaling system, phosphorylates crucial proteins and has been implicated in the pathophysiology of depression and suicide. The objective of the study was to examine if changes in PKA activity or in the protein and messenger RNA (mRNA) expression of any of its subunits are related to the pathophysiology of teenage suicide. We determined PKA activity and the protein and mRNA expression of different subunits of PKA in cytosol and membrane fractions obtained from the prefrontal cortex, (PFC) hippocampus, and nucleus accumbens (NA) of post-mortem brain from 17 teenage suicide victims and 17 nonpsychiatric control subjects. PKA activity was significantly decreased in the PFC but not the hippocampus of teenage suicide victims as compared with controls. However, the protein and mRNA expression of only two PKA subunits, that is, PKA RIalpha and PKA RIbeta, but not any other subunits were significantly decreased in both membrane and cytosol fractions of the PFC and protein expression of RIalpha and RIbeta in the NA of teenage suicide victims as compared to controls. A decrease in protein and mRNA expression of two specific PKA subunits may be associated with the pathogenesis of teenage suicide, and this decrease may be brain region specific, which may be related to the specific behavioral functions associated with these brain areas. Whether these changes in PKA subunits are related to suicidal behavior or are a result of suicide or are specific to suicide is not clear at this point.

Low-protein diets reduce PKAalpha expression in islets from pregnant rats

We investigated the effect of protein restriction on insulin secretion and the expression of protein kinase (PK)Aalpha and PKCalpha in islets from control and pregnant rats. Adult control nonpregnant (CN) and control pregnant (CP) rats were fed a normal-protein diet (17%), whereas low-protein nonpregnant (LPN) and low-protein pregnant (LPP) rats were fed a low-protein diet (6%) for 15 d. In the presence of 2.8 and 8.3 mmol glucose/L, insulin secretion by islets of CP rats was higher than that by islets of CN rats. Compared with the CN groups, insulin secretion by islets of LPN rats was lower with 8.3 but not with 2.8 mmol glucose/L. The insulin secretion by islets of LPP rats was higher than by LPN rats at both glucose concentrations. IBMX (1 mmol/L), a phosphodiesterase inhibitor, increased insulin secretion by islets from pregnant rats, and this effect was greater in islets of CP rats than in LPP rats. Forskolin (0.01-100 micromol/L), a stimulator of adenylyl cyclase, increased insulin secretion only in islets of CN and CP rats, with a higher 50% effective concentration in islets of CP rats compared with CN rats. The insulin secretion induced by phorbol 12-myristate 13-acetate (a stimulator of PKC) was higher in islets of LPN and LPP rats than in the respective controls, especially at 8.3 mmol glucose/L. PKAalpha, but not PKCalpha, expression was lower in islets of rats fed low protein than in the controls, regardless of the physiological status of the rats. All endocrine cells of the islets, including beta-cells, expressed the PKAalpha isoform. The cytoplasmic distribution of this enzyme in beta-cells was not modified by pregnancy and/or protein restriction. In conclusion, our results indicate that the response of islets from rats fed low protein during pregnancy is similar to that of control rats, at least for physiologic glucose concentration. However, the decreased response to IBMX and forskolin indicates decreased production and/or sensitivity to cAMP; this was associated with a decrease in PKA expression, which may result in lower PKA activity.

Diabetes-related changes in cAMP-dependent protein kinase activity and decrease in relaxation response in rat mesenteric artery

Using superior mesenteric artery rings isolated from age-matched controls and streptozotocin (STZ)-induced diabetic rats, we recently demonstrated that EDHF-type relaxation is impaired in STZ-induced diabetic rats, possibly due to a reduced action of cAMP via increased phosphodiesterase (PDE) activity (Matsumoto T, Kobayashi T, and Kamata K. Am J Physiol Heart Circ Physiol 285: H283-H291, 2003). Here, we investigated the activity and expression of cAMP-dependent protein kinase (PKA), an enzyme that is produced by a pleiotropic and plays key roles in the transduction of many external signals through the cAMP second messenger pathway and in cAMP-mediated vasorelaxation. The relaxation induced by cilostamide, a selective PDE3 inhibitor, was significantly weaker in superior mesenteric artery rings from STZ-induced diabetic rats than in those from age-matched controls. The relaxation responses to 8-bromo-cAMP (8Br-cAMP) and N6,O2-dibutyryl-adenosine-cAMP (db-cAMP), a cell-permeant cAMP analog, were also impaired in the STZ diabetic group. PKA activity in the db-cAMP-treated mesenteric artery was significantly lower in the STZ diabetic group. The expression levels of the mRNA and protein for PKA catalytic subunit Cat-alpha were significantly decreased in the STZ diabetic group, but those for PKA regulatory subunit isoform RII-beta were increased. We conclude that the abnormal vascular relaxation responsiveness seen in STZ-induced diabetic rats may be attributable not only to increased PDE activity but also to decreased PKA activity. Possibly, the decreased PKA activity may result from an imbalance between PKA catalytic and regulatory subunit expressions.

Protein kinase A in postmortem brain of depressed suicide victims: altered expression of specific regulatory and catalytic subunits

BACKGROUND

We recently reported reduced [3H]cyclic adenosine monophosphate binding and catalytic activity of protein kinase A in prefrontal cortex of depressed suicide victims. Here we examined the molecular basis of these alterations and whether these findings can be replicated in another cohort.

METHODS

Prefrontal cortex from depressed suicide victims and nonpsychiatric controls were obtained from the Lenhossek Human Brain Program, Budapest and the Maryland Brain Collection Program. [3H]cyclic adenosine monophosphate binding and protein kinase A activity were determined by radioligand binding and enzymatic assay, respectively. Expression of catalytic and regulatory subunits was determined by quantitative reverse transcription polymerase chain reaction and Western blot, respectively.

RESULTS

[3H]cyclic adenosine monophosphate binding and total and endogenous protein kinase A activity were significantly decreased in membrane and cytosol fractions of prefrontal cortex of depressed suicide victims from the Budapest cohort, with a similar magnitude (33%-40% reduction) as reported for the Maryland cohort. In both cohorts, selective reduction (36%-41%) in mRNA and protein expression of the regulatory RIIbeta and the catalytic Cbeta was observed.

CONCLUSIONS

Our results suggest abnormalities in [3H]cyclic adenosine monophosphate binding and catalytic activity kinase A in brain of depressed suicide victims, which could be due to reduced expression of RIIbeta and Cbeta. These abnormalities in PKA may be critical in the pathophysiology of depression.

Decreased insulin secretion in islets from rats fed a low protein diet is associated with a reduced PKAalpha expression

A low protein diet has been shown to affect the amount and activity of several enzymes and to decrease insulin secretion by islets isolated from rats fed such a diet. To understand the mechanisms involved in this phenomenon, we investigated the effects of forskolin, a stimulator of adenylyl cyclase, on insulin secretion by pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without 10 micromol forskolin/L. The forskolin-induced insulin secretion was higher in islets from NP rats than in those from LP rats (P<0.05). Western blotting revealed that the amount of the alpha catalytic subunit of protein kinase A (PKAalpha) was 35% lower in islets from LP rats than in islets from NP rats (P<0.05). Moreover, PKAalpha mRNA expression was reduced by 30% in islets from LP rats (P<0.05). Our results indicated a possible relationship between a low protein diet and a reduction in PKAalpha expression. These alterations in PKAalpha may be responsible in part for the decreased insulin secretion by islets from rats fed a low protein diet.

Activation of the cAMP-dependent protein kinase signaling pathway by luteinizing hormone in trout theca layers

In the fish ovary, LH is the main factor regulating the production of steroids during the periovulatory period and its effects are believed to be mediated, at least partially, through the cAMP-dependent protein kinase (PKA) signaling pathway. However, there is no direct evidence for the presence of PKA in the fish ovary nor on the regulation of its activity by fish LH. Here, we show the identification of regulatory (R) and catalytic (C) subunits of PKA in trout theca cells by immunoblotting. DEAE-cellulose chromatography of theca cell extracts indicated the presence of PKA type I and II and showed that trout theca cells display PKA-specific phosphotransferase and cAMP-binding activities. Salmon LH (sLH) stimulated PKA activity and increased the levels of immunoreactive RIIalpha, RIIbeta and C subunits in trout theca layers. These observations, coupled with the sLH-dependent decrease in the half-life of the C subunit, as shown by pulse-chase experiments, strongly suggest that sLH activates PKA in trout theca cells. Furthermore, our results suggest that ovarian PKA activity and its regulation by LH has been well conserved from fish to humans.

Cyclic AMP regulates expression of the RI alpha subunit of cAMP-dependent protein kinase through an alternatively spliced 5' UTR

The present study examines novel mechanisms that regulate levels of the RI alpha subunit of cAMP-dependent protein kinase. We found that RI alpha protein is induced threefold by 8-(4-chlorophenyl)thio-cAMP in hormone responsive rat Sertoli cells, while total RI alpha mRNA is not correspondingly induced. Two RI alpha mRNA isoforms with different 5' untranslated sequences (RI alpha 1a and RI alpha 1b) are produced from the RI alpha gene in Sertoli cells. Deletion/mutation analysis of the cAMP-response-element-containing promoter upstream of the RI alpha exon 1b revealed that while mutation of the cAMP response element had no effects on cAMP-mediated induction, a 73-bp region of the RI alpha exon 1b itself conferred a fivefold to eightfold induction of reporter activity to homologous and heterologous promoters. The responsiveness of this region was dependent on a sense orientation downstream of the promoter start sites and had no effect on reporter mRNA, indicating that the cAMP-mediated induction occurs at the post-transcriptional level. Modeling of the RI alpha 1b 5' UTR secondary structure revealed a 5' CAP-proximal, strong stem-loop presenting an element similar to multiple start-site element downstream-1 (GCTCGG) in the loop region. RNA-EMSAs performed with the labeled RI alpha 1b 5' UTR showed stabilization of a protein/RNA complex in extracts from 8-(4-chlorophenyl)thio-cAMP stimulated Sertoli cells. This complex was abolished by mutation of the multiple start-site element downstream-1-like element. Our findings indicate that there is a cAMP-mediated induction of RI alpha expression at the post-transcriptional level, dependent on the 5' UTR of RI alpha 1b mRNA.

Down-regulation of cyclic-nucleotide phosphodiesterase 3B in 3T3-L1 adipocytes induced by tumour necrosis factor alpha and cAMP

We have used murine 3T3-L1 cells, which differentiate in culture and acquire morphological and biochemical features of mature adipocytes, as a model for studying the expression of cyclic-nucleotide phosphodiesterase (PDE) 3B activity, protein and mRNA during differentiation and during long-term treatment of the cells with tumour necrosis factor alpha (TNF-alpha), a cytokine associated with insulin resistance, and a cAMP analogue, N(6),2'-O-dibutyryl cAMP (dbcAMP). PDE3B activity, protein and mRNA could be detected 4 days after the initiation of differentiation of 3T3-L1 preadipocytes. Treatment of 3T3-L1 adipocytes with 10 ng/ml TNF-alpha for 24 h produced a maximal (50%) decrease in PDE3B activity, protein and mRNA, which was well correlated with both activation of protein kinase A (PKA) and stimulation of lipolysis, presumably reflecting an increase in intracellular cAMP concentration. To investigate the effect of cAMP on PDE3B we treated 3T3-L1 adipocytes with dbcAMP. After 4 h with 0.5 mM dbcAMP, PDE3B activity was decreased by 80%, which was also correlated with a decrease in PDE3B protein and mRNA. This effect was abolished in the presence of N-[2-(bromocinnamylamino)ethyl]-5-isoquinolinesulphonamide] (H-89), a specific PKA inhibitor. We conclude that the lipolytic effect of TNF-alpha involves the down-regulation of PDE3B, which is associated with increased activation of PKA, presumably owing to increased levels of cAMP. In addition, the PKA activation induced by dbcAMP resulted in the down-regulation of PDE3B. These results, which suggest that PDE3B is a novel target for long-term regulation by TNF-alpha and cAMP, could contribute to the understanding of the mechanisms of insulin resistance.

Differential localization of protein kinase A type II isozymes in the Golgi-centrosomal area

Selectivity in the action of cAMP may be mediated by compartmentalized pools of cyclic AMP-dependent protein kinase (PKA). PKA type II is directed to different subcellular loci by interaction of the type II regulatory subunits (RIIalpha, RIIbeta) with A-kinase anchoring proteins. In order to separately investigate the subcellular localization of PKA type II isozymes, monospecific antibodies to human RIIalpha and RIIbeta subunits of PKA were developed. We demonstrate that centrosomes bind both RIIalpha and RIIbeta. Centrosomes were the preferred intracellular anchoring site for RIIbeta. However, centrosomal localization of RIIbeta was observed only in some highly differentiated cells such as keratinocytes, granulosa cells, and macrophages and in all neoplastic cell lines examined. Centrosomal localization of RIIbeta was not observed in normal undifferentiated cells such as fibroblasts, myoblasts, and T and B cells. In contrast, RIIalpha was abundant in the Golgi area and in the trans-Golgi network (TGN). Furthermore, although RIIalpha appeared to colocalize with microtubules in the Golgi/TGN, extractions with nonionic detergent demonstrated that RIIalpha was mainly membrane-associated. In addition, alterations of microtubule dynamics with Nocodazole or Taxol affected the distribution of the detergent-extractable pool of RIIalpha, indicating that RIIalpha may localize with microtubule-associated vesicles. Thus, RIIalpha and RIIbeta clearly localize differently in the Golgi-centrosomal region. This indicates specific roles for PKA isozymes containing either RIIalpha or RIIbeta.

Diminished Levels of Protein Kinase A RIα and RIβ Transcripts and Proteins in Systemic Lupus Erythematosus T Lymphocytes

Deficient type I protein kinase A phosphotransferase activity occurs in the T cells of 80% of subjects with systemic lupus erythematosus (SLE). To investigate the mechanism of this deficient isozyme activity, we hypothesized that reduced amounts of type I regulatory (RI) isoform transcripts, RIα and RIβ, may be associated with a diminution of RIα and/or RIβ protein. Sixteen SLE subjects with a mean (±1 SD) SLE disease activity index of 12.4 ± 7.2 were studied. Controls included 16 normal subjects, six subjects with primary Sjögren’s syndrome (SS), and three subjects with SS/SLE overlap. RT-PCR revealed that normal, SS, SS/SLE, and SLE T cells expressed mRNAs for all seven R and catalytic (C) subunit isoforms. Quantification of mRNAs by competitive PCR revealed that the ratio of RIα mRNA to RIβ mRNA in normal T cells was 3.4:1. In SLE T cells there were 20 and 49% decreases in RIα and RIβ mRNAs (RIβ; p = 0.008), respectively, resulting in an RIα:RIβ mRNA of 5.3:1. SS/SLE T cells showed a 72.5% decrease in RIβ mRNA compared with normal controls (p = 0.01). Immunoblotting of normal T cell RIα and RIβ proteins revealed a ratio of RIα:RIβ of 3.2:1. In SLE T cells, there was a 30% decrease in RIα protein (p = 0.002) and a 65% decrease in RIβ protein (p &lt; 0.001), shifting the ratio of RIα:RIβ protein to 6.5:1. T cells from 25% of SLE subjects lacked any detectable RIβ protein. Analysis of several lupus T cell lines demonstrated a persistent deficiency of both proteins, excluding a potential effect of disease activity. In conclusion, reduced expression of RIα and RIβ transcripts is associated with a decrement in RIα and RIβ proteins and may contribute to deficient type I protein kinase A isozyme activity in SLE T cells.

Cyclic-AMP-dependent protein kinase (PKA) in testicular cells. Cell specific expression, differential regulation and targeting of subunits of PKA

LH and FSH regulate via cyclic adenosine 3'5' cyclic monophosphate (cAMP) and cAMP-dependent protein kinase (PKA), steroid biosynthesis is Leydig and Sertoli cells, respectively. Cyclic AMP also regulates a number of different cellular processes such as cell growth and differentiation, ion channel conductivity, synaptic release of neurotransmitters, and gene transcription. The principle intracellular target for cAMP in mammalian cells is the PKA. The fact that this broad specificity protein kinase mediates a number of discrete physiological responses following cAMP engagement, has raised the question of how specificity is maintained in the cAMP/PKA system. Here we describe features of this signaling pathway that may contribute to explain how differential effects of cAMP may be contributed to features of the PKA signaling pathway.

Isozymes of cyclic AMP-dependent protein kinases (PKA) in human lymphoid cell lines: levels of endogenous cAMP influence levels of PKA subunits and growth in lymphoid cell lines

Activation of the cAMP signaling pathway in lymphoid cells is known to inhibit cell proliferation of T and B cells as well as cytotoxicity of natural killer (NK) cells. In order to find suitable model systems to study cAMP-mediated processes, we have examined the expression of cAMP-dependent protein kinase (PKA), endogenous levels of cAMP, and cell proliferation in eight cell lines of B lineage origin, four cell lines of T lineage origin, and normal human B and T cells. We demonstrated that the expression of mRNA and protein for one of the regulatory (R) subunits of PKA (RIalpha) was present in all the cells investigated, in contrast to the other R subunits (RIbeta, RIIalpha, and RIIbeta). Furthermore, three T cell lines and one B cell line expressed only RIalpha and C, implying these cells to contain solely PKA type I. Moreover, for the RI subunit, we observed an apparent reciprocal relationship between levels of mRNA and protein. Generally, RIalpha protein was low in cell lines where mRNA was elevated and vice versa. This was not the case for the RII subunits, where high levels of mRNA were associated with elevated levels of protein. Interestingly, we demonstrated an inverse correlation between levels of endogenous cAMP and cell growth as determined by [3H]-thymidine incorporation and cell-doubling rate (P < 0.05). Taken together, our results demonstrate great differences in PKA isozyme composition, which should be taken into consideration when using lymphoid cell lines as model system for cAMP/PKA effects in normal lymphocytes.

Structure, function, and regulation of human cAMP-dependent protein kinases

A large number of hormones, neurotransmitters, and other signaling substances that bind to G-protein-coupled cell-surface receptors have their signals converge at one sole second messenger, cAMP. The question of how specificity can be maintained in a signal-transduction system in which many extracellular signals leading to a vast array of intracellular responses are all mediated through one second-messenger system has been the subject of thorough investigation and a great deal of speculation. An increasing number of cAK isozymes, consisting of homo- or heterodimers of R subunits (RIalpha, RIbeta, RIIalpha, RIIbeta) with associated catalytic subunits (C alpha, Cbeta, Cgamma), may, at least in part, explain this specificity. The various cAK isozymes display distinct biochemical properties, and the heterogeneous subunits of cAK reveal cell-specific expression and differential regulation at the level of gene transcription, mRNA stability, and protein stability in response to a wide range of hormones and other signaling substances. The existence of a number of anchoring proteins specific to either RIIalpha or RIIbeta, and which localize cAKII isozymes toward distinct substrates at defined subcellular loci, strongly supports the idea that specific functions can be assigned to the various cAK isozymes. The demonstration that selective activation of cAKI is necessary and sufficient for cAMP-mediated inhibition of T-cell proliferation, and the observation that T-cell activation is associated with redistribution and colocalization of cAKI to the TCR, is also compatible with the notion of isozyme-specific effects.

Specific testicular cellular localization and hormonal regulation of the PKIalpha and PKIbeta isoforms of the inhibitor protein of the cAMP-dependent protein kinase

We have previously demonstrated that there exist two distinct genes for the thermostable inhibitor protein of the cAMP-dependent protein kinase, PKIalpha and PKIbeta (Van Patten, S. M., Howard, P., Walsh, D. A., and Maurer, R. A. (1992) Mol. Endocrinol. 6, 2114-2122). We have also shown that in the testis, at least eight forms of PKIbeta exist, differing as a result of at least post-translational modification and alternate translational initiation (Kumar, P., Van Patten, S. M., and Walsh, D. A. (1997) J. Biol. Chem. 272, 20011-20020). We now report that in the testis, there is a unique cellular distribution of protein kinase inhibitor forms, with PKIbeta being essentially (if not exclusively) a germ cell protein and PKIalpha being expressed primarily in Sertoli cells. Furthermore, there is a progressive change in the forms of PKIbeta that are present within germ cells with development that is initiated in testis tubules and continues as the germ cells migrate through the epididymis. These conclusions are derived from studies with isolated cell populations and with the at/at germ cell-deficient mouse line, by in situ hybridization, and by following the developmental expression of these proteins in both testis and epididymis. We have also shown that follicle-stimulating hormone (FSH) can increase the expression of both PKIalpha and PKIbeta. The FSH-regulated expression of PKIalpha in the Sertoli cell likely occurs via the normal route of second messenger signal transduction. In contrast, the FSH-dependent PKIbeta expression must arise by some form of Sertoli cell-germ cell intercommunication.

Gonadotropin-releasing hormone and pituitary adenylate cyclase-activating polypeptide affect levels of cyclic adenosine 3',5'-monophosphate-dependent protein kinase A (PKA) subunits in the clonal gonadotrope alphaT3-1 cells: evidence for cross-talk between PKA and protein kinase C pathways

We have shown previously that protein kinase A (PKA) subunit levels are regulated by activation of PKA or protein kinase C (PKC) in anterior pituitary cells. GnRH also influenced PKA subunit levels, suggesting that hormonal regulation occurs in gonadotrophs, and therefore, we have reexamined this question using the clonal gonadotrope-derived cell line (alphaT3-1 cells). Western blot analysis, using specific immunoaffinity purified immunoglobulins, revealed expression of catalytic (Cat) and regulatory type I (RI) and type II (RII) subunits of PKA in these cells. Activation of adenylyl cyclase (AC) with forskolin, or of PKC with tetradecanoyl phorbol acetate (TPA), caused a rapid (detectable at 0.5-1 h) and concentration-dependent loss of all PKA subunits. Forskolin (10-100 microM) reduced Cat and RI by 60% and RII by 30%, whereas TPA (0.1-1 microM) reduced Cat and RII by 50% and RI by 40%. Simultaneous activation of PKA and PKC caused the expected dose-dependent reductions in Cat, and the effects of forskolin or TPA were nearly additive. RI and RII were reduced similarly by 10 nM TPA, whereas 100 nM TPA tended to prevent the reduction of RI or RII caused by forskolin. GnRH, which activates phosphoinositidase C and not AC in these cells, caused a clear loss of Cat or RII at all concentrations tested and of RI at 0.1 nM. Pituitary adenylate cyclase-activating polypeptide 38, which acts via PVR-1 receptors to stimulate both phosphoinositidase C and AC in these cells, also caused a clear dose-dependent decrease in Cat, RI, and RII, although higher concentrations were needed for the latter effects. Together, the data demonstrate that catalytic and regulatory subunits of PKA are subject to both hormonal and receptor-independent regulation in alphaT3-1 cells, reinforcing the possibility that such effects occur in nonimmortalized gonadotropes. Whereas the effects of PKA activators very likely involve proteolytic degradation of the dissociated PKA holoenzyme, the effects of TPA and GnRH occur in the absence of cAMP elevation by unknown mechanisms. Whatever the mechanisms involved, the data reveal a mechanism for cross-talk between phosphoinositidase C and AC-mediated hormonal signals, in which PKC activation seems to play a pivotal role.

Characterization of the 5'-flanking region of the gene for the cAMP-inducible protein kinase A subunit, RIIbeta, in Sertoli cells

Activation of cyclic AMP-dependent protein kinases (protein kinase A, PKA) by gonadotropins and cyclic AMP (cAMP) plays an important role in the regulation of testicular functions. A regulatory subunit, RIIbeta, of PKA is transcriptionally induced in rat Sertoli cells in response to treatment with cAMP. The present study addresses regulatory mechanisms leading to increased transcription of the rat RIIbeta gene. We have localized a footprint which overlaps one of the major transcription initiation sites in the basal promoter (-293 to -123). One of the proteins binding this sequence belongs to the NF-1 family of transcription factors. We also observed binding to a basic helix-loop-helix (bHLH) response element. Furthermore, transfection studies of various 5'-deletions of the rat RIIbeta gene in primary cultures of rat Sertoli cells and in peritubular cells revealed the presence of an upstream region (-723 to -395, cAMP-responsive region) inhibiting basal expression from the rat RIIbeta gene only in Sertoli cells. This region was found to enhance cAMP responsiveness in Sertoli cells but not in peritubular cells. Interactions with downstream elements seemed to be important for the function of the cAMP-responsive region. Although some short stretches reveal homology to the cAMP-responsive regions of other slowly cAMP-responding genes, and an AP-1-like element is present, no strong resemblance to any known regulatory element responsive to cAMP is found.

Molecular cloning, upstream sequence and promoter studies of the human gene for the regulatory subunit RII alpha of cAMP-dependent protein kinase

The gene for the regulatory subunit RII alpha of cAMP-dependent protein kinase is highly regulated during spermatogenesis and a strong signal from a distinct short mRNA form is observed postmeiotically during spermatid elongation. This report presents the isolation and characterization of the 5'-flanking region (1.2 kb) and exon 1 of the human RII alpha gene. S1 nuclease mapping and primer extension experiments revealed the presence of a major transcriptional start site located 208 nucleotides upstream of start for translation. The 5'-flanking region of the RII alpha gene did not contain a TATA box and was highly G/C-rich. A basal promoter directing high levels of chloramphenicol acetyl transferase (CAT) activity was identified in the 5'-flanking sequence. Several potential binding sites for transcription factors were identified in this region, which may be responsible for the germ cell-specific regulation of this gene. We have previously reported that the human testis RII alpha cDNA contains a region (amino acids 45-75) with little or no homology to the corresponding rat skeletal muscle cDNA (Oyen, O., Myklebust, F., Scott, J.D., Cadd, G.G., McKnight, G.S., Hansson, V. and Jahnsen, T. (1990) Biol. Reprod. 43, 46-54). We examined whether this difference could arise due to organ-specific splice mechanisms or represented a species difference. We show that the low homology region of the human RII alpha cDNA resides entirely within exon 1, and does not originate from a tissue-specific alternate splicing of this distinct region.

Coordinate suppression of myeloma-specific genes and expression of fibroblast-specific genes in myeloma X fibroblast somatic cell hybrids

In most instances, fusion of differentiated cell types with fibroblasts has resulted in the extinction of the differentiation-specific traits of the non-fibroblast parental cell. To explore the genetic basis of this phenomenon, we have studied a series of somatic cell hybrids between mouse myeloma and fibroblasts. All the hybrids were adherent having a fibroblast-like phenotype. Molecular analysis revealed that plasma cell specific genes like the productively rearranged Ig genes, the J chain gene and genes for the cell surface markers CD20 and PC1, were extinguished in the hybrids. In contrast, fibroblast specific genes like fibronectin, alpha 2(I) and III collagens, as well as the receptor for fibroblast growth factor (flg), were expressed. Extinction was not due to chromosomal loss or lack of the relevant genes. To learn about the mechanism(s) of this phenomenon we have looked for the presence of positive and negative transcription factors in our hybrids. Expression of the PU.1 transcription factor, a member of the Ets transcription factor family normally expressed in B cells and macrophages, was lost in the cell hybrids. Interestingly, we found that the B-cell-specific Oct-2 transcription factor was still expressed at somewhat variable levels in several of the hybrid cell lines. In contrast, expression of the recently identified octamer coactivator BOB.1/OBF.1 was extinguished in all cell hybrids. This supports a critical role of this transcriptional coactivator for B-cell-specific gene expression. In addition, the Id and HLH462 genes coding for proteins known to repress bHLH transcription factors by formation of heterodimers, were found to be expressed at increased levels in fibroblasts and in the hybrids, indicating that their increased levels might also contribute to the suppression of myeloma-specific genes. Our results show that in myeloma x fibroblast hybrids, the phenotype of the fibroblast is dominant. It is suggested that fibroblasts contain regulatory "master" genes that are responsible for activation of the fibroblast differentiation pathway and suppress differentiation programs of other cell types.

Patterns of cyclic AMP-dependent protein kinase gene expression during ontogeny of the murine palate

Normal growth and differentiation of embryonic palatal tissue depends on regulated levels of intracellular cAMP. Cyclic AMP-dependent protein kinases (PKA) act to mediate the biological activities of cAMP. PKA isozyme protein profiles demonstrate a clear pattern of temporal alterations in embryonic palatal tissue during its development. In order to ascertain the molecular basis for changing PKA isozyme profiles during palatal ontogeny, the spatial and temporal expression of mRNAs for regulatory (RI alpha, RII alpha, and RII beta) and catalytic (C alpha) subunits of PKA was examined. RNA extracted from murine embryonic palatal tissue (days 12-14 of gestation) was examined by Northern blot analysis. Significant levels of constitutively expressed RI alpha and C alpha mRNA were seen on all days of gestation examined. RI alpha transcripts were substantially less abundant in palate mesenchymal cells in vitro than in palatal tissue in vivo. Levels of RII alpha and RII beta mRNA were highest on gestational day (GD) 12, a period characterized by pronounced palatal tissue growth. In addition, patterns of tissue distribution of RII beta, not previously described, were examined in the developing embryonic palate. A dramatic developmental shift in tissue distribution of RII beta was seen. The isozyme was evenly distributed between palatal epithelial and mesenchymal cells on GD 12 but by GD 14, RII beta was predominantly localized to palatal epithelial cells. Direct activation of adenylate cyclase with forskolin in murine embryonic palate mesenchymal (MEPM) cells resulted in an increase in RII alpha mRNA levels but had no effect on steady state levels of RII beta or C alpha mRNA. In addition, elevation of intracellular levels of cAMP resulted in a shift in the transcriptional profile of RI alpha mRNAs. Results of this study document specific patterns of expression for the genes encoding the various cAMP-dependent protein kinase regulatory and C alpha subunits in murine embryonic palatal tissue. In addition, we have demonstrated adaptational changes of this kinase in MEPM cells in response to conditions of increased intracellular levels of cAMP.

Follicle-stimulating hormone regulation of AP-1: inhibition of c-jun and stimulation of jun-B gene transcription in the rat Sertoli cell

The proto-oncogenes c-fos and c-jun and the related jun-B encode the components of transcription factor, AP-1, a heterodimeric DNA-binding protein that mediates hormone and growth factor-regulated gene expression. In the rat Sertoli cell, FSH rapidly inhibited c-jun gene expression while it stimulated c-fos and jun-B as well as the expression of the more slowly responding, tissue plasminogen activator (tPA) and inhibin alpha-subunit. These early effects of FSH were not inhibited by cycloheximide. Nuclear run-off analyses demonstrated that the FSH-dependent decline in c-jun and increases in c-fos, jun-B, tPA and inhibin alpha-subunit mRNAs were regulated at the transcriptional level. The rates of degradation of c-fos, c-jun and jun-B mRNAs were unaffected by FSH while tPA and inhibin alpha-subunit mRNAs were stabilized. After 8 h of FSH treatment, the transcription of all five genes returned to basal rates. These data demonstrate immediate-early regulation by FSH of the expression of genes encoding components of the transcription factor, AP-1.

Extinction of tyrosine aminotransferase gene activity in somatic cell hybrids involves modification and loss of several essential transcriptional activators

Extinction is defined as the loss of cell type-specific gene expression that occurs in somatic cell hybrids derived by fusion of cells with dissimilar phenotypes. To explore the basis of this dominant-negative regulation, we have studied the activities of the control elements of the liver-specific gene encoding tyrosine aminotransferase (TAT) in hepatoma/fibroblast hybrid crosses. We show that extinction in complete somatic cell hybrids is accompanied by the loss of activity of all known cell type-specific control elements of the TAT gene. This inactivity is the result of first, lack of expression of genes coding for the transcriptional activators HNF4 and HNF3 beta and HNF3 gamma, which bind to essential elements of the enhancers; and second, loss of in vivo binding and activity of ubiquitous factors to these enhancers, including CREB, which is the target for repression by the tissue-specific extinguisher locus TSE1. Complete extinction of TAT gene activity is therefore a multifactorial process affecting all three enhancers controlling liver-specific and hormone-inducible expression. It results from lack of activation, rather than active repression, and involves both post-translational modification and loss of essential transcriptional activators.

Developmental changes in cyclic AMP-dependent protein kinase associated with increased secretory capacity of Manduca sexta prothoracic glands

In Manduca sexta, basal and PTTH-stimulated secretion of ecdysteroids by prothoracic glands in vitro increases from days 1 to 4 of the fifth larval stage. Glandular content of cAMP-dependent protein kinase was analyzed to determine if the enzyme changes in concert with increased secretory response. Photoaffinity labeling with [32P]8-N3 cAMP revealed a 55-kDa cAMP-binding protein characteristic of the regulatory subunit of type-II cAMP-dependent protein kinase (RII). It appears that RII is one of a limited number of cellular proteins that is phosphorylated in the presence of [gamma-35S]ATP; the thiophosphorylated protein and the photoaffinity-labeled regulatory subunit possess the same M(r) and pI, and thiophosphorylation is blocked by mammalian cAMP-dependent protein kinase inhibitor. From days 1 to 4 of the fifth instar, glandular content of RII increases in conjunction with increased ecdysteroid secretory capacity. Application of JH analog on day 1 significantly inhibits the observed increase in RII. Catalytic subunit activity does not change from days 1 to 4 of the fifth instar, nor does cellular content of a 34-kDa protein previously shown to be phosphorylated in response to PTTH. While it is unlikely that increased content of RII is solely responsible for enhanced ecdysteroid secretion by the prothoracic glands, it may serve as a convenient marker for investigating the mechanism by which steroidogenic capacity is regulated.

Cyclic AMP-dependent protein kinase in human embryonic palate mesenchymal cells

Growth and differentiation of cells derived from the embryonic palate are critically dependent on the intracellular cAMP-mediated signal transduction pathway. Human embryonic palate mesenchymal (HEPM) cells have been widely used to examine the effect of teratogens on palatal tissue growth and differentiation, as well as a prescreen for environmental teratogens. This study examined responsiveness of HEPM cells to agents known to stimulate adenylate cyclase, characterized cAMP-dependent protein kinases (cAMP-dPK) (EC 2.7.1.37) and investigated to what extent HEPM cells reveal adaptational responses to cAMP at the level of cAMP-dependent protein kinase. HEPM cells exhibited a total cell cycle transit time of approximately 22 h and responded maximally, when confluent, to prostacyclin (PGI2), prostaglandin E2 (PGE2), and isoproterenol with time- and dose-dependent increases in intracellular levels of cAMP. The order of sensitivity to hormonal activation of adenylate cyclase was PGE2 > isoproterenol > PGI2. Basal cAMP-dependent protein kinases activity was 0.184 fmol phosphate transferred from ATP to histone per microgram protein per minute under conditions where endogenous phosphatases did not significantly affect protein phosphorylation. Regulatory subunits of cAMP-dPK in HEPM cells were characterized by the binding of [3H]cAMP to cytosolic fractions. Specific binding was saturable at approximately 50 nM indicating the presence of binding sites that are finite in number. Calculation of half-maximal binding yielded an estimated Kd of 25 nM indicating the presence of high affinity binding sites. Cyclic AMP-dPK regulatory subunits were also photoaffinity labeled with 8-N3-[32P]-cAMP, subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and radiolabeled bands visualized by autoradiography. Photoactivated incorporation of 8-N3-[32P]cAMP was detected into two proteins of molecular weight (M(r)) 45,000 and M(r) 51,000 representing, respectively, the RI alpha and RII beta subunits of cAMP-dPK. Binding of [32P]8-azido cAMP to proteins of M(r) 45,000 (RI alpha) and M(r) 51,000 (RII beta) was increased in response to elevation of intracellular cAMP via inhibition of its breakdown with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, or by direct activation of adenylate cyclase with forskolin. HEPM cells thus revealed adaptational responses to cAMP at the level of cAMP-dependent protein kinase. Characterization of the cAMP signal transduction pathway in HEPM cells, derived from embryonic palatal tissue which is critically dependent on this pathway for normal development, may provide information fundamental to a clear understanding of cellular events involved in palatal ontogeny. These results highlight several important differences between HEPM cells and murine embryonic palate mesenchymal cells.(ABSTRACT TRUNCATED AT 400 WORDS)

cAMP-dependent protein kinases in the rat testis: regulatory and catalytic subunit associations

Based upon recent reports that the rat testis exhibits mRNAs for cAMP-dependent protein kinase (A-kinase) regulatory (R) subunits RI alpha, RI beta, RII alpha, and RII beta, this study was designed to identify R proteins present in extracts of germ cell-rich testis from adult and Sertoli cell-enriched, germ cell-poor testis from 14-15-day-old rats. Following separation by DEAE-cellulose, R subunits were identified by Mr: (a) upon labeling with 8-N3[32P]cAMP and 32P in an RII phosphorylation reaction and; (b) by Western blot analysis using R-specific antibodies on one- and two-dimensional gel electrophoresis. Elution of R subunits as catalytic (C) subunit-free dimers or in association with C subunits to form holoenzyme was determined by their sedimentation characteristics on sucrose gradient centrifugation in conjunction with their cAMP-stimulated activation characteristics on Eadie-Scatchard analysis. Soluble extracts of testes, from both adult and 14-15 day-old rats, showed the presence of a prominent type I holoenzyme containing RI alpha subunits (47 kDa, peak 1), a minor type II holoenzyme, containing RII beta subunits (52 kDa, peak 2), and a second, more abundant, type II holoenzyme peak containing predominantly RII alpha and, to a lesser extent RII beta subunits (peak 3). The 53 kDa RI beta protein predicted by mRNA studies was only tentatively identified by Western blot analysis. Testes extracts of 14-15-day-old, but not adult, rats exhibited high levels of C subunit-free RI alpha, a result not predicted by mRNA studies. This latter result may be attributable to direct RI alpha regulation or to indirect RII beta regulation at a time during testis development prior to germ cell maturation.

Half-lives of different sized mRNAs for the PKA subunit RI alpha are regulated differently in response to inhibition of transcription and translation

The RI alpha mRNA level is induced 3-5 times by FSH or cAMP analogs in primary cultures of rat Sertoli cells. In rat tissues, the RI alpha gene gives rise to three different mRNAs of different size: 3.2, 2.9 and 1.7 kb. In the present study we report that the 1.7 kb transcript has a shorter half-life than the two other mRNAs. In cells which had been pre-stimulated with a cAMP analog, inhibition of transcription stabilizes the two larger, but not the smaller sized RI alpha mRNA. However, in contrast, inhibition of protein synthesis stabilizes all the RI alpha mRNAs. Thus, degradation of various mRNAs coding for the same protein reveals different dependencies on transcription and translation.

Inhibitors of RNA and protein synthesis stabilize messenger RNA for the RII beta subunit of protein kinase A in different cellular compartments

Messenger RNA for RII beta is transiently induced (greater than 50-fold) by cAMP analogs in primary cultures of rat Sertoli cells. The induction is dependent on protein synthesis. We have previously shown that mRNA for RII beta is stabilized by cAMP, as well as inhibitors of transcription and translation. This indicated that rapid degradation of RII beta mRNA involved a protein with a rapid turnover and its corresponding mRNA. The two RNA synthesis inhibitors used in the present study stabilized both nuclear and cytoplasmic RII beta mRNA, whereas inhibition of protein synthesis stabilized RII beta mRNA in the cytoplasm only. These results indicate that only cytoplasmic degradation of RII beta mRNA is dependent on a protein with high turnover. In contrast, nuclear degradation appears to be dependent on an RNA with a short half-life, not involving protein synthesis.

Suramin inhibits gonadotropin action in rat testis: implications for treatment of advanced prostate cancer

Suramin is being evaluated for the treatment of metastatic prostate cancer based on its inhibition of growth factor action. In addition, suramin may inhibit the endocrine control of androgen production, which was explored herein. Adult Sprague-Dawley rats were injected (i.p.) daily with varying doses of suramin. At a cumulative dose of 200 mg., suramin significantly depressed serum testosterone (p less than 0.05), and follicle stimulating hormone (p less than 0.002) levels. In vitro studies showed that suramin-mediated suppression of androgen production might be secondary to inhibition of gonadotropin action. In MA-10 cell cultures, suramin inhibited a maximum stimulatory dose of human chorionic gonadotropin with an ED50 of 4.4 microM. Studies in rat Sertoli cell cultures showed that follicle stimulating hormone action was also inhibited by suramin, with an ED50 of 8.6 microM. Using receptor binding assays with calf testis membrane, we showed that suramin inhibited 125I-hFSH binding to receptor in a dose dependent fashion with an ED50 of 10.4 microM; comparable to the ED50 of suramin inhibition of follicle stimulating hormone action in Sertoli cell culture cells. Thus the mechanism of suramin's suppression of androgen production may involve multiple sites of action, including inhibition of gonadotropin binding to its receptor and suppression of pituitary gonadotropin levels in serum. This inhibition of androgen production may be useful in the treatment of advanced prostate cancer.

The tissue-specific extinguisher locus TSE1 encodes a regulatory subunit of cAMP-dependent protein kinase

The tissue-specific extinguisher locus TSE1, a dominant negative regulator of transcription in somatic cell hybrids, acts via a cAMP response element (CRE) to repress activity of a hepatocyte-specific enhancer. Guided by the antagonism between TSE1 and cAMP-mediated signal transduction, we identified the regulatory subunit RI alpha of protein kinase A (PKA) as the product of the TSE1 locus. The evidence derives from concordant expression of RI alpha mRNA and TSE1 genetic activity, high resolution mapping of the RI alpha gene and TSE1 on human chromosome 17, and the ability of a transfected RI alpha cDNA to generate a phenocopy of TSE1-mediated extinction. The mechanism of TSE1/RI alpha-mediated extinction involves repression of basal PKA activity, reduced phosphorylation of CREB at Ser-133, and a corresponding reduction of in vivo protein binding at the target CRE.

Molecular cloning and characterization of the promoter region of the mouse regulatory subunit RII beta of type II cAMP-dependent protein kinase

The promoter and exon 1 of the regulatory subunit (RII beta) of type II cAMP-dependent protein kinase were isolated from a mouse genomic library. The 5'-flanking DNA lacked TATA and CAAT sites but contained GC rich regions typically found in constitutively expressed house keeping genes. Fusion gene constructs, containing RII beta 5'-flanking sequences and the bacterial CAT structural gene, were transfected into NB2a neuroblastoma cells and CHO cells. The NB2a cells expressed high levels of CAT activity. CHO cells expressed CAT activity at 5% of the level seen in the NB2a cells. Transfection of deletion constructs into both cell lines was used to define the core promoter and enhancer elements. The core promoter was situated between bp -291/-121. An enhancer element was located between bp -1426/-1018.

Protein kinase C activation selectively increases mRNA levels for one of the regulatory subunits (RI alpha) of cAMP-dependent protein kinases in HT-29 cells

We have examined the effect of the protein kinase C activator, TPA, on mRNA levels for subunits of cAMP-dependent protein kinases in the human colonic cancer cell line HT-29, subline m2. Messenger RNA for the regulatory subunit, RI alpha, of cAMP-dependent protein kinases was shown to be present and regulated by TPA. Other mRNAs for subunits of cAMP-dependent protein kinases (RI beta, RII alpha, RII beta, C alpha, C beta) were also present in these cells, but revealed no or only minor changes upon TPA stimulation. When HT-29 cells were cultured in the presence of 10 nM TPA for various time periods, a biphasic response was observed in RI alpha mRNA levels with a maximal increase (approximately 4 fold) after 24 hours. TPA stimulated RI alpha mRNA increased in a concentration-dependent manner and maximal response (4-8 fold) was seen at 3-10 nM. The TPA-induced increase in RI alpha mRNA was not obtained when cells were incubated with TPA together with the protein kinase C inhibitors, staurosporine or H7. The cAMP-analog 8-CPTcAMP alone induced RI alpha mRNA levels 50% more than TPA. Combined treatment with TPA (10 nM) and 8-CPTcAMP (0.1 mM) gave an increase in RI alpha mRNA similar to TPA. These results demonstrate an interaction between the protein kinase C pathway and mRNA levels for the RI alpha subunit of cAMP-dependent protein kinases in HT-29 cells.

Rat RI beta isoform of type I regulatory subunit of cyclic adenosine monophosphate-dependent protein kinase: cDNA sequence analysis, mRNA tissue specificity, and rat/mouse difference in expression in testis

A rat complementary DNA (cDNA) for the RI beta isoform of type I cyclic adenosine monophosphate (cAMP)-dependent protein kinase regulatory subunit was cloned and sequenced and was found to contain the entire protein coding and 3'-untranslated regions, with a single (ATTAAA) poly-adenylation site. The largest open reading frame was preceded by a short out-of-phase open reading frame, which is not seen in the corresponding mouse RI beta cDNA due to a single base substitution. The rat RI beta cDNA clone was 2,374 bases long and detected a rat mRNA of approximately 2.8 kilobases. Rat RI beta mRNA was abundant in adult rat brain and testis but was undetectable in other rat tissues. The rat RI beta cDNA also detected RI beta mRNA in mouse brain, but not mouse testis, from 10-week-old BALB/c or 10- and 6-week-old Swiss Webster mice. Thus, despite a 96% nucleotide identity in the coding region of RI beta in rat vs. mouse, there are at least two differences in these closely related species. First, there is a short open reading frame, which precedes the coding region in the rat but not the mouse. Second, unlike the mouse testis, the rat testis contains abundant levels of RI beta mRNA.