The alpha-subunit mRNAs for Gs and Go2 are differentially regulated by protein kinase A and protein kinase C in rat Sertoli cells

PCTK1 regulates integrin-dependent spindle orientation via protein kinase A regulatory subunit KAP0 and myosin X

Integrin-dependent cell-extracellular matrix (ECM) adhesion is a determinant of spindle orientation. However, the signaling pathways that couple integrins to spindle orientation remain elusive. Here, we show that PCTAIRE-1 kinase (PCTK1), a member of the cyclin-dependent kinases (CDKs) whose function is poorly characterized, plays an essential role in this process. PCTK1 regulates spindle orientation in a kinase-dependent manner. Phosphoproteomic analysis together with an RNA interference screen revealed that PCTK1 regulates spindle orientation through phosphorylation of Ser83 on KAP0, a regulatory subunit of protein kinase A (PKA). This phosphorylation is dispensable for KAP0 dimerization and for PKA binding but is necessary for its interaction with myosin X, a regulator of spindle orientation. KAP0 binds to the FERM domain of myosin X and enhances the association of myosin X-FERM with β1 integrin. This interaction between myosin X-FERM and β1 integrin appeared to be crucial for spindle orientation control. We propose that PCTK1-KAP0-myosin X-β1 integrin is a functional module providing a link between ECM and the actin cytoskeleton in the ECM-dependent control of spindle orientation.

Phorbol myristate acetate induces changes on F-actin and vinculin content in immature rat Sertoli cells

Actin and vinculin are two of the most abundant cytoskeletal proteins, widely expressed in nearly all types of eukaryotic cells. It has been well established that long-term exposure to the tumor promoter phorbol myristate acetate (PMA) affects Sertoli cell morphology, as well as F-actin and vinculin organization in vitro. To analyze in a quantitative manner the F-actin and vinculin content of rat immature Sertoli cells in vitro in response to PMA exposure, cytoskeletal fractions were prepared following extraction with Triton X-100. Analysis of the isolated cytoskeletal fractions by immunoblotting showed that exposure of immature rat Sertoli cells to PMA for 8h has an appreciable effect on the cellular level of both the actin and vinculin. Interestingly, as revealed by using calphostin C, a specific protein kinase C inhibitor, the observed F-actin and vinculin changes are most probably mediated by a mechanism that depends on protein kinase activity. A discussion is made concerning PKC modulation by PMA and the subsequent actin and vinculin quantitative changes and reorganization, phenomena that have been closely related to cell transformation.

Activation of serum- and glucocorticoid-induced protein kinase (Sgk) by cyclic AMP and insulin

Sgk (serum- and glucocorticoid-induced protein kinase) is a serine/threonine-specific protein kinase that is transcriptionally regulated by serum, glucorticoids, and mineralocorticoids. Sgk regulates the amiloride-sensitive sodium channel in kidney principal cells. Insulin and insulin-like growth factor-1 stimulate activity of Sgk by a mechanism mediated by phosphoinositide-dependent kinases (PDK)-1 and -2. In this study, we demonstrate that incubation of transfected cells with 8-(4-chlorophenylthio)-cAMP (8CPT-cAMP; 0.2 mm) led to a 2-fold activation of recombinant Sgk expressed in COS7 cells. Furthermore, the combination of insulin plus 8CPT-cAMP elicited a larger response than either agent alone. The effect of insulin was inhibited by wortmannin (100 nm), but not by the cyclic AMP-dependent protein kinase (PKA) inhibitor, H89 (10 microm). As expected, the effect of 8CPT-cAMP was completely blocked by H89. Surprisingly, the effect of 8CPT-cAMP was also inhibited by wortmannin, suggesting that phosphorylation of Sgk by PDK-1 and/or -2 is required for activation by 8CPT-cAMP. Mutational analysis led to similar conclusions. The Thr(369) --> Ala mutant, lacking the PKA phosphorylation site, was activated by insulin but not 8CPT-cAMP. In contrast, the Ser(422) --> Ala mutant, lacking a PDK-2 phosphorylation site, was inactive and resistant to activation by either insulin or 8CPT-cAMP. In summary, Sgk is subject to complex regulatory mechanisms. In addition to regulation at the level of gene expression, the enzymatic activity of Sgk is regulated by multiple protein kinases, including PKA, PDK-1, and PDK-2. Cross-talk among these signaling pathways may play an important role in the pathogenesis of the hypertension associated with hyperinsulinemia, obesity, and insulin resistance.

Cyclic AMP regulates G(omicronalpha) protein and mRNA levels by modulating the transcriptional rate of G(omicronalpha) gene

In rat astroglial cells, four G(omicronalpha) transcripts were found: G(omicron2alpha) mRNA (5.7 kb) and three G(omicron1alpha) mRNAs (4.0, 3.0 and 2.3 kb). However, G(omicron2alpha) but little G(omicronalpha1) proteins were present in membrane-enriched fractions. Culturing astroglial cells with forskolin (10 microM) or isoproterenol (10 microM) a beta-adrenergic agonist increased transiently in a time-dependent manner the levels of G(omicronalpha) proteins. The degradation rate of G(omicronalpha) proteins was slightly decreased by the cAMP treatment. In parallel, forskolin (10 microM) treatment increased transiently the amounts of both G(omicron1alpha) and G(omicron2alpha) mRNAs. The relative transcription rate of G(omicronalpha) gene was increased by 1.7-fold in forskolin-treated cells whereas the half-lives of G(omicron1alpha) and G(omicron2alpha) mRNAs were not significantly changed. These results suggest that cAMP regulates the transcription rate of G(omicronalpha) gene and this is compatible with the existence of a cAMP responsive element in the promoter of the G(omicronalpha) gene.

The in vitro effect of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate on Sertoli cell morphology

The objective of the present study was to examine the effects of the well-known tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) on the morphology of cultured Sertoli cells from immature rats. The cells were cultured for 5 days and the TPA was added at the end of the culture period for 8 h at a concentration of 10-7 M. Viability tests showed that controls as well as TPA-treated cells remained viable during the culture period and no deleterious effects were observed as a result. Application of computerized morphometry at both light and electron microscopic levels revealed that TPA caused important changes in cell morphology in vitro. Statistical analysis of the results indicated that compared to the controls, Sertoli cells treated with TPA exhibited fewer astrocytic-type cytoplasmic extensions and a smaller size. Our results support the conclusion that the tumor promoter TPA, when applied to immature Sertoli cells in vitro, causes significant morphological alterations.

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.

Modulation of gonadotropic and purinergic responsiveness by islet activating protein in sertoli cells from immature rats

In the present study we have examined the effects of islet activating protein (IAP) on the regulatory effects of FSH, glucagon and (-)N6-(R)-phenyl-isopropyladenosine (PIA), an adenosine A1 receptor agonist, on the formation of cAMP and estradiol-17 beta (E2) in Sertoli cell cultures isolated from immature (19-day-old) rats. FSH (NIH-FSH-S-15) (1.25 micrograms/ml) caused a more than 10-fold stimulation of the level of both cAMP and E2 in the spent media from Sertoli cell cultures during an 18 h incubation. Both responses were reduced by 80% in the presence of PIA (10(-6) M). When the cultures were preincubated for 24 h with increasing concentration of IAP, the inhibitory effects of PIA were counteracted in a concentration-dependent manner. Moreover, preincubation with IAP (> 20 ng/ml) caused a significant stimulation of FSH-stimulated cAMP production even in the absence of PIA. PIA inhibited FSH-stimulated cAMP production in a concentration dependent manner. However, when the cells were preincubated with IAP (100 ng/ml) for 24 h, the inhibitory effects of PIA were completely abolished, and PIA now actually caused a slight stimulation of cAMP production. Both FSH and glucagon stimulated cAMP production in a concentration-dependent manner. Preincubation with IAP (100 ng/ml for 24 h) resulted in an increase in maximal stimulation of cAMP production for both FSH and glucagon. When adenylyl cyclase (AC) activity was measured directly in isolated membrane particles from Sertoli cells cultured in the presence of IAP (100 ng/ml) for 24 h, both basal and FSH-stimulated AC activity were significantly higher than in membrane particles from control cells. These results provide a further characterization of the functional Gi component coupled to the AC complex in cultured rat Sertoli cells, mediating the inhibitory effects of adenosine and possibly other endogenous substances on cAMP production.