Interleukin-10 gene promoter polymorphism in Japanese patients with adult and early-onset periodontitis

BACKGROUND

IL-10 is an anti-inflammatory cytokine, which may modulate disease expression in chronic inflammatory periodontal disease. 3 dimorphic polymorphisms within the IL-10 gene promoter have recently been identified and appear to influence regulation of its expression.

AIM

The aim of the present study was to investigate whether the promoter polymorphisms are associated with adult periodontitis (AP) and generalized early-onset periodontitis (G-EOP).

METHODS

Genomic DNA was obtained from 34 AP patients, 18 G-EOP patients and 52 controls. The promoter region between -506 and -1140 was amplified by polymerase chain reaction, and polymorphisms were detected by nucleotide sequencing.

RESULTS

The haplotype frequencies in Japanese were quite different from those of Caucasian and were even slightly different from those of southern Chinese with systemic lupus erythematosus. We found no significant difference in allele or haplotype frequencies between patients and controls.

CONCLUSIONS

IL-10 production may be regulated within the complex cytokine network in chronic inflammatory periodontal disease, rather than the gene polymorphisms.

Analysis of treatment outcome after stereotactic radiosurgery for cavernous sinus meningiomas

OBJECT

The long-term outcome of stereotactic radiosurgery for cavernous sinus (CS) meningiomas is not fully understood. The authors retrospectively reviewed their experience with 40 CS meningiomas treated with gamma knife radiosurgery.

METHODS

Follow-up periods for the 40 patients ranged from 12 to 123 months (median 42 months), and the overall tumor control rates were 86.4% at 3 years and 82.3% at 10 years. Factors associated with tumor recurrence in univariate analysis were histological malignancy (p < 0.0001), partial treatment (p < 0.0001), suprasellar tumor extension (p = 0.0201), or extension in more than three directions outside the CS (p = 0.0345). When the tumor was completely covered with a dose to the margin that was higher than 14 Gy (Group A, 22 patients), no patient showed recurrence within the median follow-up period of 37 months. On the other hand, when a part of the tumor was treated with 10 to 12 Gy (Group B, 15 patients) or did not receive radiation therapy (Group C, three patients), the recurrence rates were 20% and 100%, respectively. Neurological deterioration was seen in nine patients, but all symptoms were transient or very mild.

CONCLUSIONS

The data indicate that stereotactic radiosurgery can control tumor growth if the whole mass can be irradiated by dosages of more than 14 Gy. When optimal radiosurgical planning is not feasible because of a tumor's large size, irregular shape, or proximity to visual pathways, use of limited surgical resection before radiosurgery is the best option and should provide sufficient long-term tumor control with minimal complications.

Successful treatment of patients with rheumatic disorders and acquired factor VIII inhibitors with cyclophosphamide and prednisolone combination therapy: two case reports

Acquired haemophilia associated with autoimmune disorders can be fatal and has been reported to be refractory to steroid therapy alone. We report two cases of female patients, aged 24 years and 54 years, with acquired haemophilia caused by factor VIII inhibitors. Underlying diseases were systemic lupus erythematosus in the 24-year-old patient and rheumatoid arthritis in the 54-year-old patient. Both conditions were nearly quiescent when the patients manifested haemorrhagic diathesis. In response to combination therapy with prednisolone and cyclophosphamide, coagulation abnormalities were resolved together with complete elimination of factor VIII inhibitors in both patients. Thus, combination therapy with alkylating agents may be recommended as initial therapy for the management of autoimmune patients with factor VIII inhibitors.

Insulin-independent and wortmannin-resistant targeting of IRS-3 to the plasma membrane via its pleckstrin homology domain mediates a different interaction with the insulin receptor from that of IRS-1

AIMS/HYPOTHESIS

In primary adipocytes, although IRS-1 and IRS-3 are expressed in comparable amounts, these proteins manifest distinct distribution and significance in insulin signalling. We investigated the molecular basis of the difference between these two proteins.

METHODS

In Cos-1 cells transiently expressing rat IRS-1, IRS-3, or chimeric proteins of these two proteins we examined the tyrosine phosphorylation via the wild-type or mutant insulin receptors and evaluated their targeting to the plasma membrane by immunostaining the membrane ghost.

RESULTS

In contrast to IRS-1, IRS-3 was tyrosine-phosphorylated by the insulin receptor altering Tyr960 to Phe (Y960F), which disrupts the binding site of the PTB domain of IRSs, to an extent comparable to the wild-type receptor. The tyrosine phosphorylation of IRS-3 with the PH domain replacement via the Y960F insulin receptor markedly decreased, whereas that of IRS-3 with the PTB domain alteration was mildly impaired. Insulin-stimulated translocation of IRS-1 to the plasma membrane, as well as that of IRS-3 with the PH domain replacement, was wortmannin-sensitive, although that of IRS-3 was insulin-independent and wortmannin-resistant.

CONCLUSIONS/INTERPRETATION

The affinity of the PH domain for the phospholipids in the plasma membrane seems to influence the receptor-substrate interaction required for IRS tyrosine phosphorylation, indicating that the PH domain and the PTB domain of IRSs cooperatively function in insulin-stimulated tyrosine phosphorylation of these proteins.

Vascular endothelial growth factor C gene expression is closely related to invasion phenotype in gynecological tumor cells

OBJECTIVE

The correlation between the gene expression of various angiogenic factors and in vitro invasive activity in 16 human gynecological cancer cell lines was investigated.

METHODS

Semiquantitative reverse transcription polymerase chain reaction analysis was performed to investigate the mRNA expression levels of vascular endothelial growth factors (VEGF-A, -B, -C, and -D), basic fibroblast growth factor (bFGF), and matrix metalloproteinase (MMP)-2 with beta-actin coamplified as an internal standard. Tumor cell migration along a gradient of substratum-bound fibronectin and invasion into reconstituted basement membrane were evaluated by haptotactic migration and invasion assay.

RESULTS

Expression of VEGF-A mRNA was detected in all 16 cell lines, whereas the relative expression levels of other VEGF family members and bFGF, differed markedly among the cell lines. There was a statistical correlation between VEGF-C gene expression and the number of cells that migrated and invaded (P < 0.01). However, expression of mRNAs of other angiogenic factors did not correlate with motility and invasive activity of the cells. Moreover, there was a close correlation between VEGF-C and MMP-2 gene expression levels (P < 0.05).

CONCLUSION

Tumor cells that produce VEGF-C may have a higher invasive and metastatic potential because of their capacity to pass through tissue barriers.

Risk of aneurysm recurrence in patients with clipped cerebral aneurysms: results of long-term follow-up angiography

BACKGROUND AND PURPOSE

With many patients living long after microsurgical aneurysm clipping for subarachnoid hemorrhage (SAH) and with the evolution of intravascular procedures as less invasive alternatives, knowledge of the long-term results of clipping is becoming important.

METHODS

Of 412 patients who underwent clipping of ruptured or unruptured cerebral aneurysms at our institution between 1976 and 1994 and who survived >3 years after surgery, 225 patients who were in good general condition and younger than 80 years were offered follow-up angiography to detect newly formed aneurysms. Of the 225, 80 patients (35.6%) agreed to undergo angiography. In addition, 32 patients underwent angiography for new medical indications other than SAH. Therefore, 112 patients underwent angiography, representing a total of 140 clipped aneurysms.

RESULTS

The mean interval from surgery was 9.3 years for all patients and 9.0 years for the clipped aneurysms (range 3 to 21 years). Four aneurysm regrowths were detected of the 140 (2.9%) clipped aneurysms, representing 3 of 125 completely clipped aneurysms, 1 of 14 incompletely clipped aneurysms, and 0 of 1 aneurysm not studied with postoperative angiography. De novo aneurysms were detected in 9 of 112 (8.0%) patients. The annual rate of de novo aneurysm formation was 0.89%.

CONCLUSIONS

This study shows that the annual rate of de novo aneurysm formation is relatively high (0.89%) and that the cumulative risk becomes significant after 9 years. In consideration of the fatality rate of SAH, follow-up angiography may be indicated for patients with clipped aneurysms 9 to 10 years after surgery.

Correlation between thymidine phosphorylase expression and invasion phenotype in cervical carcinoma cells

The correlation between thymidine phosphorylase (dThdPase) expression and invasion phenotype in human uterine cervical carcinoma cells was investigated using 10 cervical carcinoma cell lines. Semi-quantitative reverse transcription-polymerase chain reaction analysis was performed to investigate the mRNA levels of dThdPase and matrix metalloproteinase (MMP)-2 with beta-actin coamplified as an internal standard. dThdPase protein expression levels were detected by highly sensitive enzyme-linked immunosorbent assay. Tumor cell migration along a gradient of substratum-bound fibronectin and invasion into reconstituted basement membrane were evaluated by haptotactic migration and invasion assay. Although dThdPase mRNA and protein expression levels differed remarkably among the cell lines, there was a statistical correlation between them (r = 0.743, p = 0.0139). dThdPase gene and protein expression levels were well correlated with the number of cells that migrated and invaded (p < 0.05). Moreover, there was a close correlation between MMP-2 gene and dThdPase gene and protein expression levels (p < 0.05). Tumor cells that produce dThdPase may have a higher invasive and metastatic potential because of their capacity to pass through tissue barriers.

Corticosteroid therapy in patients with IgA nephropathy and impaired renal function

AIM

IgA nephropathy (IgAN) is a common type of primary glomerulonephritis that constitutes a major cause of end-stage renal disease. Oral and/or intravenous glucocorticoid therapy can protect against progression of IgAN in patients with preserved renal function. We evaluated steroid therapy in IgAN with established renal dysfunction.

PATIENTS AND METHODS

We retrospectively analyzed the effect of methylprednisolone (MP) pulse therapy in 8 IgAN patients with serum creatinine concentrations (sCr) 2.76 +/- 1.32 mg/dl (mean +/- SD). In each patient renal function had progressively deteriorated in the 12 months preceding treatment, as indicated by negative slopes of 1/sCr plotted against time (regression coefficients).

RESULTS

Regression coefficients during the 12 months following therapy improved significantly from -0.02333 +/- 0.00732 to -0.00036 +/- 0.00423 dl/mg/month, respectively. The mean difference in slope was 0.0230 +/- 0.0076 dl/mg/month (95% confidence interval, 0.0165 to 0.0295, p < 0.001). Proteinuria also significantly decreased from a mean urine protein/creatinine ratio of 2.57 +/- 1.12 before therapy to 1.12 +/- 0.84 6 months after therapy (p < 0.005). Other factors that might affect progression of renal dysfunction remained unchanged during the observation periods.

CONCLUSION

Corticosteroids may attenuate progression of renal failure and delay the need for dialysis in this patient population, although a large randomized trial is necessary.

Silencing of the caspase-1 gene occurs in murine and human renal cancer cells and causes solid tumor growth in vivo

Renal cell cancer is a unique solid tumor that occasionally shows spontaneous regression even at an advanced stage, of which the underlying mechanism is not well understood. To investigate a potential role of the pro-apoptotic molecule caspase-1 in the growth regulation of renal cell cancer, we created transfectants expressing exogenous caspase-1 from a murine renal cancer cell line, Renca. Overexpression of caspase-1 did not affect the growth of Renca cells in vitro at the exponential phase but induced apoptotic cell death at 50% to 75% confluence, whereas control cells underwent apoptosis only after reaching 100% confluence. When implanted into the flank of a syngeneic BALB/c mouse, caspase-1-overexpressing Renca cells did not effectively establish growth as a solid tumor, forming a measurable tumor in only 7 of 11 (64%) animals, whereas control cells formed a tumor in 6 of 6 (100%) animals. The growth of tumors from caspase-1-overexpressing cells slowed down markedly after the tumors reached 5 to 10 mm in diameter, and histological examination of such tumors revealed numerous apoptotic cells positively stained by TUNEL assay. Interestingly, endogenous caspase-1 was not detected in the tumors from control cells, which re-expressed caspase-1 when they were re-cultured and exposed to a demethylation reagent, 5-aza-2'-deoxycytidine. Furthermore, treatment of a human renal cancer cell line, ACHN, with 5-aza-2'-deoxycytidine also caused recovery of caspase-1 expression, which was not detected before treatment. These data suggest that silencing of caspase-1 through DNA methylation may be involved in the oncogenesis of some renal cell cancers growing as a solid tumor.

Treatment of adult Still's disease with dexamethasone, an alternative to prednisolone

We successfully treated three cases of adult Still's disease (ASD) with dexamethasone. High dose prednisolone, which was initially used to treat these patients, failed to remit the disease in all cases. Although they were resistant to prednisolone, all these patients had remarkable improvements in clinical and laboratory findings after switching to an equivalent dose of dexamethasone. We propose using dexamethasone as an alternative for treating ASD before adding immunosuppressants or disease modifying anti-rheumatic drugs (DMARD), when prednisolone therapy does not suppress disease activity sufficiently.

Radiosurgery of meningeal melanocytoma

The authors present a case of meningeal melanocytoma arising from Meckel's cave. A coal-black, vascular tumor was partially removed by surgery. Histopathologically, the tumor lacked anaplastic features. Immunohistochemical studies confirmed that the tumor was of neuroectodermal origin and had low proliferating activity. The patient underwent gamma knife radiosurgery for the residual tumor, in which 25 Gy of radiation was delivered to the tumor margin. Three years after irradiation, the tumor showed marked shrinkage without complication.

Adult Still's disease as a paraneoplastic manifestation of breast cancer

We treated a patient who developed symptoms and findings indistinguishable from those of adult Still's disease as a manifestation of metastatic breast cancer 7 years after treatment for a stage 1 tumor. Although clinical features fulfilled diagnostic criteria for adult Still's disease, examination of a bone marrow biopsy specimen indicated that the apparent adult Still's disease was a paraneoplastic manifestation associated with diffuse marrow infiltration by breast cancer. The fever and polyarthralgia resolved with administration of prednisolone, and antiestrogen therapy with tamoxifen citrate was also started.

Somatosensory-evoked potential to evaluate the trigeminal nerve after sagittal split osteotomy

OBJECTIVE

The purpose of this study was to assess the onset period of trigeminal nerve hypoesthesia during bilateral sagittal split osteotomy, with the use of the trigeminal somatosensory-evoked potential (TSEP).

STUDY DESIGN

Subjects were 10 patients with mandibular prognathism who underwent setback surgery. Intraoperative TSEP was measured 4 times: just before the commencement of the surgery, immediately after the induction of general anesthesia; after the medial periosteal dissection of the alveolar neurovascular bundle; after the sagittal split of bone; and after semirigid fixation with a titanium miniplate with the use of a monocortical screw. Postoperative TSEP was measured after the start of postoperative weeks 2, 4, 12, and 24. Normal records of the TSEP wave comprised peak (13 ms), trough (16 ms), peak (22.7 ms), and trough (36 ms) (N1, P1, N2, P2, respectively). Trigeminal hypoesthesia was assessed by the latency of P1 and N2, because they indicated the most reproducible waveforms.

RESULTS

The change in shape of the spectra indicated that prolonged latency was initiated on medial periosteal dissection and was extended further after the sagittal bone split and fixation. However, latency recovery was observed relatively quickly after the start of postoperative weeks 2 and 4.

CONCLUSIONS

Trigeminal hypoesthesia appeared to be induced by direct injury to the alveolar nerve during the bone split or by compression injury after fixation. Accordingly, the occurrence of a long-lasting postoperative trigeminal sensory hypoesthesia seemed to depend on nervous involvement of the split surface, the manner of fixation, or the intraoperative care.

Reduced urinary excretion of intact osteopontin in patients with IgA nephropathy

Osteopontin (OPN) is a phosphoprotein secreted by many cells of epithelial, mesenchymal, and hematopoietic origin. In the kidney, OPN is expressed in the renal tubules and collecting ducts and is excreted into the urine. A pathophysiologic role for urinary OPN has not been established. In this study, urinary excretion of OPN was analyzed in patients with primary glomerular diseases, including immunoglobulin A nephropathy (IgAN; n = 32), minimal change nephrotic syndrome (MCNS; n = 16), and membranous nephropathy (MN; n = 18). Compared with normal controls (n = 20), mean +/- SD of urinary OPN in IgAN patients was decreased significantly (21.4 +/- 6.2 versus 11.6 +/- 9.6 mg/g creatinine, P: < 0.001). In contrast, the levels of urinary OPN in patients with MCNS or MN did not differ significantly from normal values. Immunoblot analysis showed that OPN is present as a 55- to 60-kd molecule in normal urine. A 34-kd fragment of OPN was the major immunoreactive band in samples from IgAN patients. This fragment also was detectable in the urine from some patients with MCNS or MN but was absent in normal subjects. OPN has a thrombin-cleavage site near its central portion. Thrombin treatment of the urine from normal controls could result in 34-kd OPN fragments. Although the underlying mechanisms remain to be determined, these data provide evidence that secretion or processing (or both) of urinary OPN is altered in patients with IgAN.

Essential role of insulin receptor substrate 1 in differentiation of brown adipocytes

The most widely distributed members of the family of insulin receptor substrate (IRS) proteins are IRS-1 and IRS-2. These proteins participate in insulin and insulin-like growth factor 1 signaling, as well as the actions of some cytokines, growth hormone, and prolactin. To more precisely define the specific role of IRS-1 in adipocyte biology, we established brown adipocyte cell lines from wild-type and IRS-1 knockout (KO) animals. Using differentiation protocols, both with and without insulin, preadipocyte cell lines derived from IRS-1 KO mice exhibited a marked decrease in differentiation and lipid accumulation (10 to 40%) compared to wild-type cells (90 to 100%). Furthermore, IRS-1 KO cells showed decreased expression of adipogenic marker proteins, such as peroxisome proliferator-activated receptor gamma (PPARgamma), CCAAT/enhancer-binding protein alpha (C/EBPalpha), fatty acid synthase, uncoupling protein-1, and glucose transporter 4. The differentiation deficit in the KO cells could be reversed almost completely by retrovirus-mediated reexpression of IRS-1, PPARgamma, or C/EBPalpha but not the thiazolidinedione troglitazone. Phosphatidylinositol 3-kinase (PI 3-kinase) assays performed at various stages of the differentiation process revealed a strong and transient activation in IRS-1, IRS-2, and phosphotyrosine-associated PI 3-kinase in the wild-type cells, whereas the IRS-1 KO cells showed impaired phosphotyrosine-associated PI 3-kinase activation, all of which was associated with IRS-2. Akt phosphorylation was reduced in parallel with the total PI 3-kinase activity. Inhibition of PI 3-kinase with LY294002 blocked differentiation of wild-type cells. Thus, IRS-1 appears to be an important mediator of brown adipocyte maturation. Furthermore, this signaling molecule appears to exert its unique role in the differentiation process via activation of PI 3-kinase and its downstream target, Akt, and is upstream of the effects of PPARgamma and C/EBPalpha.

Insulin receptor substrate 3 (IRS-3) and IRS-4 impair IRS-1- and IRS-2-mediated signaling

To investigate the roles of insulin receptor substrate 3 (IRS-3) and IRS-4 in the insulin-like growth factor 1 (IGF-1) signaling cascade, we introduced these proteins into 3T3 embryonic fibroblast cell lines prepared from wild-type (WT) and IRS-1 knockout (KO) mice by using a retroviral system. Following transduction of IRS-3 or IRS-4, the cells showed a significant decrease in IRS-2 mRNA and protein levels without any change in the IRS-1 protein level. In these cell lines, IGF-1 caused the rapid tyrosine phosphorylation of all four IRS proteins. However, IRS-3- or IRS-4-expressing cells also showed a marked decrease in IRS-1 and IRS-2 phosphorylation compared to the host cells. This decrease was accounted for in part by a decrease in the level of IRS-2 protein but occurred with no significant change in the IRS-1 protein level. IRS-3- or IRS-4-overexpressing cells showed an increase in basal phosphatidylinositol 3-kinase activity and basal Akt phosphorylation, while the IGF-1-stimulated levels correlated well with total tyrosine phosphorylation level of all IRS proteins in each cell line. IRS-3 expression in WT cells also caused an increase in IGF-1-induced mitogen-activated protein kinase phosphorylation and egr-1 expression ( approximately 1.8- and approximately 2.4-fold with respect to WT). In the IRS-1 KO cells, the impaired mitogenic response to IGF-1 was reconstituted with IRS-1 to supranormal levels and was returned to almost normal by IRS-2 or IRS-3 but was not improved by overexpression of IRS-4. These data suggest that IRS-3 and IRS-4 may act as negative regulators of the IGF-1 signaling pathway by suppressing the function of other IRS proteins at several steps.

Vascular endothelial growth factor induces expression of connective tissue growth factor via KDR, Flt1, and phosphatidylinositol 3-kinase-akt-dependent pathways in retinal vascular cells

Fibroblastic proliferation accompanies many angiogenesis-related retinal and systemic diseases. Since connective tissue growth factor (CTGF) is a potent mitogen for fibrosis, extracellular matrix production, and angiogenesis, we have studied the effects and mechanism by which vascular endothelial growth factor (VEGF) regulates CTGF gene expression in retinal capillary cells. In our study, VEGF increased CTGF mRNA levels in a time- and concentration-dependent manner in bovine retinal endothelial cells and pericytes, without the need of new protein synthesis and without altering mRNA stability. VEGF activated the tyrosine receptor phosphorylation of KDR and Flt1 and increased the binding of phosphatidylinositol 3-kinase (PI3-kinase) p85 subunit to KDR and Flt1, both of which could mediate CTGF gene induction. VEGF-induced CTGF expression was mediated primarily by PI3-kinase activation, whereas PKC and ERK pathways made only minimal contributions. Furthermore, overexpression of constitutive active Akt was sufficient to induce CTGF gene expression, and inhibition of Akt activation by overexpressing dominant negative mutant of Akt abolished the VEGF-induced CTGF expression. These data suggest that VEGF can increase CTGF gene expression in bovine retinal capillary cells via KDR or Flt receptors and the activation of PI3-kinase-Akt pathway independently of PKC or Ras-ERK pathway, possibly inducing the fibrosis observed in retinal neovascular diseases.

Temporomandibular joint morphology and disc position in skeletal class III patients

INTRODUCTION

The purpose of this study was to investigate the relationship between temporomandibular joint (TMJ) morphology, including discal tissue and clinical symptoms in class III dentofacial deformity patients.

MATERIAL AND METHODS

Forty-four patients were examined with lateral, frontal and axial cephalograms. They were divided into two groups, consisting of a class III symmetry and a class III asymmetry group. By using magnetic resonance imaging the 88 joints could be classified into four types on the basis of disc position and shape: anteriorly displaced disc, anterior type, fully-covered type and posterior type. Furthermore, TMJ morphology was measured tomographically in the sagittal plane.

RESULTS

Anteriorly displaced discs in the asymmetry group (56.8%) occurred significantly more frequently than in the symmetry group (18.2%; p <0.05). TMJ symptoms (clicking, crepitus, closed lock, pain) were seen in 17/44 joints (38.6%) of the symmetry and 24/44 joints (54.5%) of the asymmetry group, for a total of 41/88 joints (46.6%). There were no differences in joint space ratio and condyle ratio. However, the fossa ratio on the deviation side was significantly higher than on the nondeviation side in the asymmetry group (p<0.05).

CONCLUSION

The incidence of internal derangement in asymmetrical class III patients is higher than in symmetrical mandibular prognathism, and this difference is associated with a difference in TMJ morphology of both sides.

Plasma levels of myeloperoxidase and elastase are differentially regulated by hemodialysis membranes and anticoagulants

To examine effects of dialyzer membranes and anticoagulants on hemodialysis (HD)-triggered neutrophil degranulation. We measured plasma myeloperoxidase (MPO) and elastase (ELT) by an enzyme-linked immunoabsorbent assay. During routine HD with a cuprophane membrane and high molecular weight (HMW) heparin, plasma MPO was rapidly upregulated to maximal levels within 15 min after starting extracorporeal circulation. In contrast, the level of plasma ELT gradually increased such that the highest level was achieved at the end of the procedure. When polysulfone and polymethylmethacrylate membranes were substituted for cuprophane, the rise in ELT was markedly suppressed. Polysulfone was also capable of reducing the MPO response, although the effect was less prominent than that for ELT. As for anticoagulants, nafamostat mesylate (NM) completely suppressed the rise in plasma MPO during HD with cuprophane. Low molecular weight (LMW) heparin also partially inhibited this response. In sharp contrast, there was no significant difference in the ELT response between nafamostat, HMW, and LMW heparins. Thus, NM maximally suppressed the rise of plasma MPO but had no effect on the ELT response. Our results suggest that neutrophil degranulation of MPO and ELT is differentially regulated during HD. Polysulfone and NM appear to maximally reduce excessive neutrophil activation.

Positive and negative regulation of phosphoinositide 3-kinase-dependent signaling pathways by three different gene products of the p85alpha regulatory subunit

Phosphoinositide (PI) 3-kinase is a key mediator of insulin-dependent metabolic actions, including stimulation of glucose transport and glycogen synthesis. The gene for the p85alpha regulatory subunit yields three splicing variants, p85alpha, AS53/p55alpha, and p50alpha. All three have (i) a C-terminal structure consisting of two Src homology 2 domains flanking the p110 catalytic subunit-binding domain and (ii) a unique N-terminal region of 304, 34, and 6 amino acids, respectively. To determine if these regulatory subunits differ in their effects on enzyme activity and signal transduction from insulin receptor substrate (IRS) proteins under physiological conditions, we expressed each regulatory subunit in fully differentiated L6 myotubes using adenovirus-mediated gene transfer with or without coexpression of the p110alpha catalytic subunit. PI 3-kinase activity associated with p50alpha was greater than that associated with p85alpha or AS53. Increasing the level of p85alpha or AS53, but not p50alpha, inhibited both phosphotyrosine-associated and p110-associated PI 3-kinase activities. Expression of a p85alpha mutant lacking the p110-binding site (Deltap85) also inhibited phosphotyrosine-associated PI 3-kinase activity but not p110-associated activity. Insulin stimulation of two kinases downstream from PI-3 kinase, Akt and p70 S6 kinase (p70(S6K)), was decreased in cells expressing p85alpha or AS53 but not in cells expressing p50alpha. Similar inhibition of PI 3-kinase, Akt, and p70(S6K) was observed, even when p110alpha was coexpressed with p85alpha or AS53. Expression of p110alpha alone dramatically increased glucose transport but decreased glycogen synthase activity. This effect was reduced when p110alpha was coexpressed with any of the three regulatory subunits. Thus, the three different isoforms of regulatory subunit can relay the signal from IRS proteins to the p110 catalytic subunit with different efficiencies. They also negatively modulate the PI 3-kinase catalytic activity but to different extents, dependent on the unique N-terminal structure of each isoform. These data also suggest the existence of a mechanism by which regulatory subunits modulate the PI 3-kinase-mediated signals, independent of the kinase activity, possibly through subcellular localization of the catalytic subunit or interaction with additional signaling molecules.