Phosphorylation of PP2Ac by PKC is a key regulatory step in the PP2A-switch-dependent AKT dephosphorylation that leads to apoptosis

BACKGROUND

Although GqPCR activation often leads to cell survival by activating the PI3K/AKT pathway, it was previously shown that in several cell types AKT activity is reduced and leads to JNK activation and apoptosis. The mechanism of AKT inactivation in these cells involves an IGBP1-coupled PP2Ac switch that induces the dephosphorylation and inactivation of both PI3K and AKT. However, the machinery involved in the initiation of PP2A switch is not known.

METHODS

We used phospho-mass spectrometry to identify the phosphorylation site of PP2Ac, and raised specific antibodies to follow the regulation of this phosphorylation. Other phosphorylations were monitored by commercial antibodies. In addition, we used coimmunoprecipitation and proximity ligation assays to follow protein-protein interactions. Apoptosis was detected by a TUNEL assay as well as PARP1 cleavage using SDS-PAGE and Western blotting.

RESULTS

We identified Ser24 as a phosphorylation site in PP2Ac. The phosphorylation is mediated mainly by classical PKCs (PKCα and PKCβ) but not by novel PKCs (PKCδ and PKCε). By replacing the phosphorylated residue with either unphosphorylatable or phosphomimetic residues (S24A and S24E), we found that this phosphorylation event is necessary and sufficient to mediate the PP2A switch, which ultimately induces AKT inactivation, and a robust JNK-dependent apoptosis.

CONCLUSION

Our results show that the PP2A switch is induced by PKC-mediated phosphorylation of Ser24-PP2Ac and that this phosphorylation leads to apoptosis upon GqPCR induction of various cells. We propose that this mechanism may provide an unexpected way to treat some cancer types or problems in the endocrine machinery.

AKTs do not translocate to the nucleus upon stimulation but AKT3 can constitutively signal from the nuclear envelope

AKT is a central signaling protein kinase that plays a role in the regulation of cellular survival metabolism and cell growth, as well as in pathologies such as diabetes and cancer. Human AKT consists of three isoforms (AKT1-3) that may fulfill different functions. Here, we report that distinct subcellular localization of the isoforms directly influences their activity and function. AKT1 is localized primarily in the cytoplasm, AKT2 in the nucleus, and AKT3 in the nucleus or nuclear envelope. None of the isoforms actively translocates into the nucleus upon stimulation. Interestingly, AKT3 at the nuclear envelope is constitutively phosphorylated, enabling a constant phosphorylation of TSC2 at this location. Knockdown of AKT3 induces moderate attenuation of cell proliferation of breast cancer cells. We suggest that in addition to the stimulation-induced activation of the lysosomal/cytoplasmic AKT1-TSC2 pathway, a subpopulation of TSC2 is constitutively inactivated by AKT3 at the nuclear envelope of transformed cells.

GqPCR-stimulated dephosphorylation of AKT is induced by an IGBP1-mediated PP2A switch

BACKGROUND

G protein-coupled receptors (GPCRs) usually regulate cellular processes via activation of intracellular signaling pathways. However, we have previously shown that in several cell lines, GqPCRs induce immediate inactivation of the AKT pathway, which leads to JNK-dependent apoptosis. This apoptosis-inducing AKT inactivation is essential for physiological functions of several GqPCRs, including those for PGF2α and GnRH.

METHODS

Here we used kinase activity assays of PI3K and followed phosphorylation state of proteins using specific antibodies. In addition, we used coimmunoprecipitation and proximity ligation assays to follow protein-protein interactions. Apoptosis was detected by TUNEL assay and PARP1 cleavage.

RESULTS

We identified the mechanism that allows the unique stimulated inactivation of AKT and show that the main regulator of this process is the phosphatase PP2A, operating with the non-canonical regulatory subunit IGBP1. In resting cells, an IGBP1-PP2Ac dimer binds to PI3K, dephosphorylates the inhibitory pSer608-p85 of PI3K and thus maintains its high basal activity. Upon GqPCR activation, the PP2Ac-IGBP1 dimer detaches from PI3K and thus allows the inhibitory dephosphorylation. At this stage, the free PP2Ac together with IGBP1 and PP2Aa binds to AKT, causing its dephosphorylation and inactivation.

CONCLUSION

Our results show a stimulated shift of PP2Ac from PI3K to AKT termed "PP2A switch" that represses the PI3K/AKT pathway, providing a unique mechanism of GPCR-stimulated dephosphorylation. Video Abstract.

Basal anti-cyclic citrullinated peptide (anti-CCP) antibody levels and a decrease in anti-CCP titres are associated with clinical response to adalimumab in rheumatoid arthritis

OBJECTIVE

To investigate the effect of adalimumab treatment on anti-cyclic citrullinated peptide antibodies (anti-CCP) in patients with rheumatoid arthritis (RA).

METHODS

70 RA patients who failed treatment with disease modifying antirheumatic drugs (DMARDs) received 40 mg adalimumab subcutaneously every other week during 24 weeks. Serum samples were collected at baseline and at weeks 8, 16 and 24 before the corresponding adalimumab dose. The serum anti-CCP levels were tested by enzyme linked immunosorbent assay.

RESULTS

At baseline, 52 of the 70 patients (74.3%) were positive for anti-CCP antibodies. 60 % of the anti CCP positive patients and 44.4% of the anti CCP negative patients were ACR 20 responders at week 24 (p<0.049). The serum levels of anti-CCP antibodies decreased significantly after 24 weeks of adalimumab treatment only in those patients who met ACR 20 response criteria at week 24 (p<0.00044). Differences between baseline anti-CCP titers and those at 8, 16 and 24 weeks were all statistically significant (p<0.014, 0.003 and 0.019 respectively). No statistically significant changes in the anti-CCP levels were observed in patients who did not meet the ACR 20 response criteria.

CONCLUSION

Basal anti-CCP antibodies levels correlate with clinical response to adalimumab. A decrease in anti-CCP levels on time was observed in patients showing also clinical improvement, suggesting that serum anti-CCP antibodies determination may be useful in assessing treatment efficacy in RA patients.

Analysis of FcgammaRII gene polymorphisms in Wegener's granulomatosis

Fcgamma receptors (FcgammaRs) are potent initiators of proinflammatory reactions and tissue injury programs through the oxidative burst, degranulation and the production of a variety of proinflammatory cytokines. Direct experimental evidence indicates that translocation of ANCA target from intracellular granules to the neutrophil membrane and subsequent binding of ANCA enables FcgammaR-mediated neutrophil activation. In the presence of ANCA, these data provide a framework from which to understand the importance of ANCA class, subclass, and titer in Wegener's granulomatosis and other ANCA-positive vasculitides. The well-characterized and functionally important alleles of neutrophil FcgammaR (FcgammaRIIa-H131/R131 and FcgammaRIIIb-NA1/NA2) are possible inheritable genetic elements that may alter disease severity and/or phenotype.

[Hepatitis C virus infection presenting as a polyarthritis: report of 2 cases]

Several disease have been associated with hepatitis C virus infections, including rheumatologic, hematologic and neoplastic disorders. We report two women, aged 57 and 39 years old whom the initial presentation of hepatitis C virus infection was an arthritis resembling rheumatoid arthritis. Laboratory work up revealed abnormal liver function tests, stimulating the search for hepatitis C virus infection, having both patients positive ELISA tests. Detection of this agent is extremely important when selecting a therapy for the articular disease, since several drugs used in the treatment of rheumatic disorders are potentially hepatotoxic and immunosuppression is risky in the setting of a viral hepatitis.

[Lyme disease in Chile. Prevalence study in selected groups]

BACKGROUND

The prevalence of Lyme disease in Chile is unknown.

AIM

To study the existence and epidemiology of Lyme disease in Chile.

PATIENTS AND METHODS

One hundred eighteen patients with signs or symptoms suggestive of Lyme disease were studied. Antibodies against Borrelia burgdorferi were measured using ELISA and indirect immunofluorescence screening tests. Positive cases were confirmed with ELISA using a purified antigen and Western Blot analysis. Human biological samples and ticks were cultured in BSK-H medium.

RESULTS

Five patients, three with dermatological manifestations and two with facial palsy and other neurological symptoms, had antibodies against Borrelia, measured by ELISA and indirect immunofluorescence. However the presence of IgM antibodies by ELISA using purified antigen, was confirmed in only one case. All sera and cerebrospinal fluids were negative on Western Blot Analysis. No plasma, skin, CSF or thick culture yielded Borrelia

CONCLUSIONS

We could not confirm the existence of Lyme disease in Chile. Positive screening with negative confirmatory test suggests false positive non-specific reactivity or that local Borrelia are antigenically different compared to North American strains.

[Tenosynovitis caused by ciprofloxacin. Clinical case]

We report a 67 years old diabetic female that received ciprofloxacin for an acute pyelonephritis. Twelve days after starting this treatment, a hand and forearm tenosynovitis appeared, that subsided after the discontinuation of ciprofloxacin. Literature review disclosed other reports of tenosynovitis associated with the use of this antimicrobial.

[Lupus erythematosus disseminatus and Pneumocystis carinii pneumonia]

We report a 49 years old woman with systemic lupus erythematosus and a WHO type IV nephropathy, treated with prednisone 1 mg/kg/day po and cyclophosphamide 1 g/month iv. After two months in this treatment schedule, she presented with an acute pneumonia; broncoalveolar lavage and lung biopsy disclosed the presence of Pneumocystis carinii. She was treated with trimethoprim-sulfamethoxazole 960 mg tid with a favorable response. Opportunistic infections are frequent in lupus erythematosus and Pneumocystis carinii pneumonia has been recently reported in this disease. The changes in immune response and the adverse effects of drugs used in its treatment may explain the increased susceptibility of these patients to infections by Pneumocystis carinii.

[Rapidly progressive kidney failure associated with neutrophil anticytoplasmic autoantibodies. Anatomo-clinical case]

We report a 63 year old woman with a rapidly progressive renal failure and fever of unknown origin. Laboratory tests showed anemia, increased ESR and a urine analysis compatible with a glomerular disease. Antineutrophil cytoplasmic autoantibodies were positive with a perinuclear pattern. Kidney biopsy showed an autoimmune crescenteric glomerulonephritis. The patient had a bad evolution, dying after a massive hemoptysis. The necropsy showed a disseminated arteritis without compromise of bronchial vessels. The oligosymptomatic presentation of this patient, bearing in mind the anatomo-pathological findings, is noteworthy and emphasizes the usefulness of serological markers as antineutrophil cytoplasmic autoantibodies in the differential diagnosis.

[Polymorphic reticulosis: a type of lymphoma? Report of 3 cases]

Three patients seen at the Medicine Department of Del Salvador Hospital between 1986 and 1990 are reported. All had a history of purulent or bloody nasal discharge and recurrent sinusitis, before the appearance of progressive and painful destructive phenomena that affected the rhino faucial region. The diagnosis was made with the histopathological study that disclosed and angiocentric polymorphic infiltrates and perivascular necrosis. The three patients received similar treatment consistent in prednisone 1 mg/kg/day per os, cyclophosphamide 2 mg/kg/day per os and local radiotherapy. The response to therapy was bad and survival was less than three months. It is concluded that although this entity is infrequent, its severity requires and aggressive workup and management by a multidisciplinary team. Notwithstanding the mortality remains to be high.

[Hepatitis by infectious mononucleosis]

Five adult patients presenting with clinical and laboratory manifestations of an acute hepatitis in the course of a hitherto undiagnosed infectious mononucleosis (IM) are reviewed. Chief complaints were intense malaise and prolonged fever (7 to 15 days prior to diagnosis). Serum aminotransferases were moderately raised in all patients; three patients had mild jaundice with a direct-reacting hyperbilirubinemia; 4 patients had an enlarged and tender liver. When making the differential diagnosis of causes of acute hepatitis, blood smear examination was crucial, showing atypical lymphocytes (Downey). The diagnosis of IM was confirmed by the demonstration of high serum titers of antibodies against Epstein-Barr virus, IgM class (4 patients) or heterophil antibodies (1 patient), plus peripheral lymph node enlargement (3 patients), splenomegaly (4 patients) and the time course of the disease. The relevance of blood smear examination as a practical tool in the diagnosis of causes of acute hepatitis is stressed.

[Problems in the diagnosis of thyroid dysfunction of the elderly adult]

Thyroid disfunction in the aged is often misdiagnosed either due to scanty symptoms, masking by other ailments or because function tests can be altered by extrathyroid causes such as chronic diseases, drugs or undernutrition. We surveyed 93 patients from 60 to 104 years old (73 females) living in geriatric homes. Most received at least 2 drugs for control of hypertension, coronary artery disease, diabetes, parkinsonism or psycho-organic deterioration. No clinical evidence of thyroid disfunction was found in 75 patients. T3 was 73.6 +/- 25.5 ng/dl, T4 7.3 +/- 1.8 micrograms/dl, TSH 2.8 +/- 0.9 uU/ml and rT3 32.2 +/- 16.3 ng/dl. Antimicrosomal antibodies were negative in all. Significant differences were found comparing these values with those obtained in 26 normal adults with mean age 39.9 years: T3 was lower and TSH and rT3 were higher in the elderly (p less than 0.0001). T3 decreased and rT3 increased in relation to age and males had significantly lower values of T3, T4 and TSH than females. Some evidence of thyroid disfunction was present in the remaining 18 patients: 9 had multinodular and/or positive antimicrosomal antibodies with euthyroid hormone levels; 6 had elevated T3, T4 and fT4 so hyperthyroidism was suspected; the remaining 3 patients had TSH levels above 20 uU/ml indicating the presence of hypothyroidism of which only one had some clinical manifestation. Thus, thyroid disfunction in the elderly + is not uncommon (3.2% of hyperthyroidism and 2.6% hypothyroidism in this series) in the absence of clinical manifestation. Treatment may improve the quality of life in these patients.