Tofogliflozin long-term effects on atherosclerosis progression and major clinical parameters in patients with type 2 diabetes mellitus lacking a history of cardiovascular disease: a 2-year extension study of the UTOPIA trial.

BACKGROUND: This study aimed to assess the long-term effects of tofogliflozin, a sodium-glucose cotransporter 2 (SGLT2) inhibitor, on atherosclerosis progression and major clinical parameters in patients with type 2 diabetes lacking an apparent history of cardiovascular disease. METHODS: This was a prospective observational 2-year extension study of the "Using TOfogliflozin for Possible better Intervention against Atherosclerosis for type 2 diabetes patients (UTOPIA)" trial, a 2-year randomized intervention study. The primary endpoints represented changes in the carotid intima-media thickness (IMT). Secondary endpoints included brachial-ankle pulse wave velocity (baPWV) and biomarkers for glucose metabolism, lipid metabolism, renal function, and cardiovascular risks. RESULTS: The mean IMT of the common carotid artery (IMT-CCA) significantly decreased in both the tofogliflozin (- 0.067 mm, standard error 0.009, p < 0.001) and conventional treatment groups (- 0.080 mm, SE 0.009, p < 0.001) throughout the follow-up period; however, no significant intergroup differences in the changes (0.013 mm, 95% confidence interval (CI) - 0.012 to 0.037, p = 0.32) were observed in a mixed-effects model for repeated measures. baPWV significantly increased in the conventional treatment group (82.7 ± 210.3 cm/s, p = 0.008) but not in the tofogliflozin group (- 17.5 ± 221.3 cm/s, p = 0.54), resulting in a significant intergroup difference in changes (- 100.2 cm/s, 95% CI - 182.8 to - 17.5, p = 0.018). Compared to the conventional treatment group, tofogliflozin significantly improved the hemoglobin A1c and high-density lipoprotein cholesterol levels, body mass index, abdominal circumference, and systolic blood pressure. The frequencies of total and serious adverse events did not vary significantly between the groups. CONCLUSIONS: Tofogliflozin was not associated with improved inhibition of carotid wall thickening but exerted long-term positive effects on various cardiovascular risk factors and baPWV while showing a good safety profile.

The Influence of Tofogliflozin on Treatment-Related Quality of Life in Patients with Type 2 Diabetes Mellitus.

INTRODUCTION: Treatment-related quality of life (QOL) is an important aspect of diabetes management. We evaluated the influence of a sodium-glucose cotransporter 2 (SGLT2) inhibitor, tofogliflozin, on treatment-related QOL in Japanese patients with type 2 diabetes mellitus (T2DM). METHODS: This is the prespecified subanalysis study of the "Using TOfogliflozin for Possible better Intervention against Atherosclerosis for type 2 diabetes patients (UTOPIA)" trial. Treatment-related QOL was evaluated at baseline, week 26, week 52, and week 104 after the initiation of the study using the Diabetes Therapy-Related QOL questionnaire (DTR-QOL). Among the 340 patients in the original UTOPIA study, a total of 252 patients (127, tofogliflozin group; 125, conventional treatment group) who completed the DTR-QOL questionnaire at baseline were the study subjects of the current subanalysis. RESULTS: The tofogliflozin and conventional treatment groups exhibited almost comparable baseline clinical characteristics, while the use of antihypertensive drugs and lipid-lowering agents was significantly lower in the tofogliflozin treatment group than in the conventional treatment group. Tofogliflozin treatment increased the total score of DTR-QOL7 from baseline (P < 0.001), while conventional treatment did not change it. There were statistically significant differences in delta change in the total DTR-QOL7 score and DTR-QOL7 Q4, Q5, Q6, and Q7 scores from the baseline to week 104 between the treatment groups. Delta changes in HbA1c (Spearman's correlation coefficient, ρ = - 0.30, P < 0.001), fasting blood glucose (ρ = - 0.16, P = 0.031), BMI (ρ = - 0.19, P = 0.008), and waist circumference (ρ = - 0.17, P = 0.024) at week 104 were negatively associated with delta change in the total QOL7 score. CONCLUSIONS: Our data indicated that tofogliflozin treatment improved treatment-related QOL compared to conventional treatment in Japanese patients with T2DM, in accordance with the improvement of major cardiovascular risk factors. TRIAL REGISTRATION: UMIN000017607.

Effect of tofogliflozin on arterial stiffness in patients with type 2 diabetes: prespecified sub-analysis of the prospective, randomized, open-label, parallel-group comparative UTOPIA trial.

BACKGROUND: Tofogliflozin, an SGLT2 inhibitor, is associated with favorable metabolic effects, including improved glycemic control and serum lipid profile and decreased body weight, visceral adipose tissue, and blood pressure (BP). This study evaluated the effects of tofogliflozin on the brachial-ankle pulse wave velocity (baPWV) in patients with type 2 diabetes (T2DM) without a history of apparent cardiovascular disease. METHODS: The using tofogliflozin for possible better intervention against atherosclerosis for type 2 diabetes patients (UTOPIA) trial is a prospective, randomized, open-label, multicenter, parallel-group, comparative study. As one of the prespecified secondary outcomes, changes in baPWV over 104 weeks were evaluated in 154 individuals (80 in the tofogliflozin group and 74 in the conventional treatment group) who completed baPWV measurement at baseline. RESULTS: In a mixed-effects model, the progression in the right, left, and mean baPWV over 104 weeks was significantly attenuated with tofogliflozin compared to that with conventional treatment (- 109.3 [- 184.3, - 34.3] (mean change [95% CI] cm/s, p = 0.005; - 98.3 [- 172.6, - 24.1] cm/s, p = 0.010; - 104.7 [- 177.0, - 32.4] cm/s, p = 0.005, respectively). Similar findings were obtained even after adjusting the mixed-effects models for traditional cardiovascular risk factors, including body mass index (BMI), glycated hemoglobin (HbA1c), total cholesterol, high-density lipoprotein (HDL)-cholesterol, triglyceride, systolic blood pressure (SBP), hypertension, smoking, and/or administration of drugs, including hypoglycemic agents, antihypertensive agents, statins, and anti-platelets, at baseline. The findings of the analysis of covariance (ANCOVA) models, which included the treatment group, baseline baPWV, and traditional cardiovascular risk factors, resembled those generated by the mixed-effects models. CONCLUSIONS: Tofogliflozin significantly inhibited the increased baPWV in patients with T2DM without a history of apparent cardiovascular disease, suggesting that tofogliflozin suppressed the progression of arterial stiffness. Trial Registration UMIN000017607. Registered 18 May 2015. ( https://www.umin.ac.jp/icdr/index.html ).

Tofogliflozin does not delay progression of carotid atherosclerosis in patients with type 2 diabetes: a prospective, randomized, open-label, parallel-group comparative study.

BACKGROUND: This study aimed to investigate the preventive effects of tofogliflozin, a selective sodium-glucose cotransporter 2 (SGLT2) inhibitor, on atherosclerosis progression in type 2 diabetes (T2DM) patients without apparent cardiovascular disease (CVD) by monitoring carotid intima-media thickness (IMT). METHODS: This prospective, randomized, open-label, blinded-endpoint, multicenter, parallel-group, comparative study included 340 subjects with T2DM and no history of apparent CVD recruited at 24 clinical units. Subjects were randomly allocated to either the tofogliflozin treatment group (n = 169) or conventional treatment group using drugs other than SGLT2 inhibitors (n = 171). Primary outcomes were changes in mean and maximum common carotid IMT measured by echography during a 104-week treatment period. RESULTS: In a mixed-effects model for repeated measures, the mean IMT of the common carotid artery (mean-IMT-CCA), along with the right and left maximum IMT of the CCA (max-IMT-CCA), significantly declined in both the tofogliflozin (- 0.132 mm, SE 0.007; - 0.163 mm, SE 0.013; - 0.170 mm, SE 0.020, respectively) and the control group (- 0.140 mm, SE 0.006; - 0.190 mm, SE 0.012; - 0.190 mm, SE 0.020, respectively). Furthermore, the tofogliflozin and the conventional treatment group did not significantly differ in the progression of the mean-IMT-CCA (mean change (95% CI) 0.008 (- 0.009, 0.025) mm, P = 0.34), along with the right (mean change (95% CI) 0.027 (- 0.005, 0.059) mm, P = 0.10) and the left max-IMT-CCA (mean change (95% CI) 0.020 (- 0.030, 0.070), P = 0.43). Similar findings were obtained even after adjusting for traditional CV risk factors and/or administration of drugs at baseline. Relative to the control treatment effects, tofogliflozin significantly reduced the HbA1c, blood glucose level, body weight/body mass index, abdominal circumference, and systolic blood pressure, and significantly increased the HDL-C. The total and serious adverse events incidences did not significantly vary between the treatment groups. CONCLUSIONS/INTERPRETATION: No IMT changes were observed between the tofogliflozin and the conventional treatment groups. However, tofogliflozin is a safe and effective treatment option for managing primary CVD risk factors in this population. Clinical Trial Registration UMIN000017607 ( https://www.umin.ac.jp/icdr/index.html ).

Rationale, Design, and Baseline Characteristics of the Utopia Trial for Preventing Diabetic Atherosclerosis Using an SGLT2 Inhibitor: A Prospective, Randomized, Open-Label, Parallel-Group Comparative Study.

INTRODUCTION: Sodium-glucose co-transporter-2 (SGLT2) inhibitors are anti-diabetic agents that improve glycemic control with a low risk of hypoglycemia and ameliorate a variety of cardiovascular risk factors. The aim of the ongoing study described herein is to investigate the preventive effects of tofogliflozin, a potent and selective SGLT2 inhibitor, on the progression of atherosclerosis in subjects with type 2 diabetes (T2DM) using carotid intima-media thickness (IMT), an established marker of cardiovascular disease (CVD), as a marker. METHODS: The Study of Using Tofogliflozin for Possible better Intervention against Atherosclerosis for type 2 diabetes patients (UTOPIA) trial is a prospective, randomized, open-label, blinded-endpoint, multicenter, and parallel-group comparative study. The aim was to recruit a total of 340 subjects with T2DM but no history of apparent CVD at 24 clinical sites and randomly allocate these to a tofogliflozin treatment group or a conventional treatment group using drugs other than SGLT2 inhibitors. As primary outcomes, changes in mean and maximum IMT of the common carotid artery during a 104-week treatment period will be measured by carotid echography. Secondary outcomes include changes in glycemic control, parameters related to ß-cell function and diabetic nephropathy, the occurrence of CVD and adverse events, and biochemical measurements reflecting vascular function. CONCLUSION: This is the first study to address the effects of SGLT2 inhibitors on the progression of carotid IMT in subjects with T2DM without a history of CVD. The results will be available in the very near future, and these findings are expected to provide clinical data that will be helpful in the prevention of diabetic atherosclerosis and subsequent CVD. FUNDING: Kowa Co., Ltd. CLINICAL TRIAL REGISTRATION: UMIN000017607.

A candidate gene approach to genetic contributors to the development of IgA nephropathy.

BACKGROUND: Genetic factors contributing to the development of IgA nephropathy remain to be elucidated. METHODS: The present multicenter cross-sectional case-control study measured genotype frequencies of 65 atherosclerotic disease-related gene polymorphisms in 230 Japanese patients with IgA nephropathy and 262 apparently healthy volunteers with estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m(2) and negative or trace proteinuria and hematuria by dipstick test [non-chronic kidney disease (CKD) participants]. Clinical characteristics at kidney biopsy of patients with IgA nephropathy and those at the study recruitment of non-CKD participants were included as covariates in multivariate logistic regression models. RESULTS: Among 31 gene polymorphisms with ≥5% of minor genotype in non-CKD participants, methionine synthase MTR A2756G (D919G) was significantly associated with IgA nephropathy using χ(2) test even after controlling for family-wise error rate by the method of Bonferroni (P = 0.044). A multivariate nonconditional logistic regression model identified MTR A2756G as a significant contributor of IgA nephropathy [2756AG and GG versus AA, odds ratio 0.42 (95% confidence interval 0.25-0.69) and 0.21 (95% confidence interval 0.06-0.68), P(trend) < 0.001]. After each patient with IgA nephropathy was randomly matched to a non-CKD participant on age (±5 years), gender, mean arterial pressure (±5 mmHg) and eGFR (±5 mL/min/1.73 m(2)), a multivariate conditional logistic regression model also verified their significant association [odds ratio 0.42 (95% confidence interval 0.18-1.00) and odds ratio 0.09 (95% confidence interval 0.01-0.73), P(trend) = 0.004]. MTR A2756G was not associated with slope of eGFR (mL/min/1.73 m(2)/year) in 230 patients with IgA nephropathy. CONCLUSION: MTR A2756G was associated with the development, but not progression, of IgA nephropathy.

Efficacy of liraglutide therapy in Japanese type 2 diabetic patients insufficiently controlled with basal-supported oral therapy.

UNLABELLED: (J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00223.x, 2012) Aims/Introduction: We assessed the efficacy of liraglutide therapy in Japanese type 2 diabetic patients insufficiently controlled with basal-supported oral therapy (BOT). MATERIALS AND METHODS: We retrospectively analyzed the data of 37 patients who had postprandial hyperglycemia (≥10.0 mmol/L) with BOT (long-acting insulin plus glimepiride) with their insulin titrated enough to keep preprandial glycemia <7.2 mmol/L, and who had their treatment changed to liraglutide monotherapy, with the subsequent addition of glimepiride, when required. Those who achieved the glycemic target at all points (preprandial glycemia <7.2 mmol/L and postprandial glycemia <10.0 mmol/L) were regarded as responders and the efficacy of liraglutide therapy was assessed. We also explored the predictive clinical characteristics associated with its efficacy. RESULTS: Daily doses of insulin and glimepiride with BOT were 14 ± 9 units and 1.5 ± 0.9 mg, respectively. After the change to liraglutide therapy, 37% of the patients appeared to be responders to the therapy, whereas 12% had their glycemic control rather deteriorated. Efficacy of liraglutide therapy was significantly associated with baseline insulin dosage and post-breakfast glycemia with BOT. The C-statistic of the model was calculated to be 0.90. CONCLUSIONS: There were responders and non-responders to liraglutide therapy in Japanese BOT failures. It is likely that baseline insulin dosage and post-breakfast glycemia with BOT are clinically useful indicators for the efficacy of liraglutide therapy.

Beneficial effects of nateglinide on insulin resistance in type 2 diabetes.

Nateglinide, a rapid insulin secretagogue, is known to facilitate the early phase of insulin secretion and has been used for the treatment of type 2 diabetic patients with postprandial hyperglycemia. The aim of this study is to evaluate the effect of nateglinide on insulin resistance as well as insulin secretory defects in type 2 diabetic patients. Insulin secretion ability was evaluated by the hyperglycemic clamp test, and insulin sensitivity was evaluated by the euglycemic hyperinsulinemic clamp test, using an artificial pancreas. The hyperglycemic clamp test showed that a 7-day treatment with nateglinide significantly increased insulin secretion in response to high glucose. Interestingly, although nateglinide is known to facilitate insulin secretion, daily urinary C-peptide excretion was decreased after nateglinide treatment. Moreover, in the euglycemic hyperinsulinemic clamp test, glucose infusion rate was significantly increased by nateglinide treatment, indicating that nateglinide functions to decrease insulin resistance. Nateglinide ameliorates insulin resistance as well as insulin secretory defects in type 2 diabetic patients.

Decreased endogenous secretory advanced glycation end product receptor in type 1 diabetic patients: its possible association with diabetic vascular complications.

OBJECTIVE: The binding of advanced glycation end products (AGEs) to their receptor (RAGE) plays an important role in the development of diabetic vascular complications. In the present study, we examined circulating endogenous secretory RAGE (esRAGE) levels in subjects with type 1 diabetes and explored the possible association between esRAGE levels and the severity of diabetic vascular complications. RESEARCH DESIGN AND METHODS: Circulating esRAGE levels in serum were examined in 67 Japanese type 1 diabetic patients (22 men and 45 women, age 24.0 +/- 4.4 years [means +/- SD]) and 23 age-matched healthy nondiabetic subjects (10 men and 13 women aged 24.9 +/- 1.4 years). Daily urinary albumin excretion, the presence of retinopathy, and intima-media thickness (IMT) of the carotid artery were also evaluated. We further explored the association between esRAGE levels and severity of diabetic vascular complications. RESULTS: Circulating esRAGE levels were significantly lower in subjects with type 1 diabetes than in nondiabetic subjects (0.266 +/- 0.089 vs. 0.436 +/- 0.121 ng/ml, respectively, P < 0.0001) and was inversely correlated with HbA(1c) (A1C) levels (r = -0.614, P < 0.0001). In addition, multivariate regression analysis demonstrated that A1C was an independent risk factor for a low esRAGE value. Furthermore, circulating esRAGE levels were inversely correlated with carotid IMT (r = -0.325, P = 0.0017) and was one of the independent risk factors for IMT thickening. Furthermore, there was a significant difference (P = 0.0124) in esRAGE levels between patients without retinopathy (0.286 +/- 0.092 ng/ml) and those with retinopathy (0.230 +/- 0.074 ng/ml). CONCLUSIONS: Circulating esRAGE levels were significantly lower in type 1 diabetic patients than in nondiabetic subjects and were inversely associated with the severity of some diabetic vascular complications.

Possible novel index determined by the glucose clamp test for selection of a suitable therapy for each type 2 diabetic patient.

The hallmark of type 2 diabetes is insulin resistance and insufficient insulin secretion, and appropriate therapy should be selected for each patient. In this study, to establish some index to select suitable therapy for each patient, we evaluated insulin sensitivity and insulin secretion with euglycemic hyperinsulinemic clamp and hyperglycemic clamp tests, respectively, and found that specific GIR index (GIRxIRI (90)) could be a useful marker to select suitable therapy for each type 2 diabetic patient (GIR: glucose infusion rate in euglycemic hyperinsulinemic clamp test; IRI (90): plasma insulin level 90 min after starting the hyperglycemic clamp test).

Association of soluble epoxide hydrolase gene polymorphism with insulin resistance in type 2 diabetic patients.

The insulin resistance found in diabetes is influenced by vascular tone and local blood flow. Endothelial-derived hyperpolarizing factor (EDHF) functions as a potent vasodilator to regulate vascular tone, and its production is regulated by soluble epoxide hydrolase (sEH). In this study, we examined the genotype distribution and allele frequency of sEH gene G860A (Arg287Gln) polymorphism in Japanese subjects (n=499) (non-diabetic subjects, n=205; type 2 diabetic patients, n=294). Also, to accurately evaluate insulin resistance, we performed the euglycemic hyperinsulinemic clamp test for each type 2 diabetic patient (n=86) from whom agreement was obtained, and then examined a possible association of sEH gene G860A polymorphism with insulin resistance status. There was no significant difference in genotype distribution and allele frequency between non-diabetic subjects and type 2 diabetic patients. Interestingly, however, there was close association of sEH gene G860A (Arg287Gln) polymorphism with insulin resistance in type 2 diabetic patients, which was not observed in non-diabetic subjects. These results suggest that sEH and EDHF play some important role in the pathogenesis of insulin resistance found in type 2 diabetes.

Association of NAD(P)H oxidase p22 phox gene variation with advanced carotid atherosclerosis in Japanese type 2 diabetes.

OBJECTIVE: To evaluate the association between the C242T polymorphism of the p22 phox gene, an essential component of NAD(P)H oxidase in the vasculature, with intima-media thickness (IMT) of the carotid artery and risk factors for atherosclerosis in type 2 diabetic subjects. RESEARCH DESIGN AND METHODS: C242T polymorphism of the p22 phox gene was detected by polymerase chain reaction-restriction fragment-length polymorphism in 200 Japanese type 2 diabetic subjects and 215 nondiabetic subjects. We examined the association with this mutation and carotid atherosclerosis as well as the patients' clinical characteristics and the level of 8-hydroxy-2'deoxyguanosine (8-OHdG) as an index of oxidative DNA damage. RESULTS: The diabetic subjects with the TC+TT genotypes displayed a significantly lower average IMT (1.13 +/- 0.31 vs. 1.31 +/- 0.34 mm; P = 0.0099) and a not significantly lower serum 8-OHdG level than those with the CC genotype, despite no difference in the risk factors. Stepwise multiple regression analysis showed that the risk factors for increased IMT in the diabetic subjects were systolic blood pressure (P = 0.0042) and p22 phox CC genotype (P = 0.0151). In nondiabetic subjects, the average IMT of the TC+TT group was not different from that of the CC group (0.85 +/- 0.14 vs. 0.94 +/- 0.30 mm, P = 0.417). Fasting plasma insulin concentration (41.4 +/- 15.6 vs. 64.2 +/- 59.4 pmol/l, P = 0.0098) and insulin resistance index of homeostasis model assessment (HOMA-R) (1.58 +/- 0.66 vs. 2.60 +/- 2.56, P = 0.0066) were significantly lower in the TC+TT group than in the CC group. CONCLUSIONS: These results show that the C242T mutation in the p22 phox gene is associated with progression of asymptomatic atherosclerosis in the subjects with type 2 diabetes and is also associated with insulin resistance in nondiabetic subjects.

NAD (P) H oxidase p22 phox C242T polymorphism affects LDL particle size and insulin resistance in Japanese subjects.

Elevated cardiovascular risk is associated with an increased number of small, dense low-density lipoprotein (LDL) particles, which exhibit increased susceptibility to lipid oxidation, however, the mechanism determining LDL particle size has never been fully elucidated. We have examined the association between the C242T polymorphism of the p22 phox gene, which is a small subunit of vascular NAD(P)H oxidase, and both LDL particle size and clinical characteristics in 260 healthy subjects. Peak LDL particle diameter (LDL-PPD) was measured by continuous disk polyacrylamide gel electrophoresis. Twenty-one of the 217 subjects with the CC genotype showed pattern B (median LDL-PPD under 25.5 nm), whereas, none of the 43 subjects with TC + TT genotypes showed pattern B. The pattern B fraction was significantly larger in the CC group than in the TC + TT group (p = 0.030). The subjects with the CC genotype also showed a significantly higher fasting glucose level, plasma insulin level, and insulin resistance index of homeostasis model assessment (HOMA-R) than those with the TC + TT genotype. Our data demonstrate that variation in the small NAD(P)H oxidase subunit p22 phox gene substantially influences LDL particle size and may also reflect differences in the insulin sensitivity of non-diabetic subjects.

Elevated C-reactive protein associates with early-stage carotid atherosclerosis in young subjects with type 1 diabetes.

OBJECTIVE: To evaluate whether low-grade inflammation contributes to early-stage advanced carotid atherosclerosis in young subjects with type 1 diabetes. RESEARCH DESIGN AND METHODS: The mean and maximum (max) intima-media thicknesses (IMT) of the carotid artery were assessed using ultrasound B-mode imaging in 55 patients with type 1 diabetes (22 men and 33 women, aged 22.1 +/- 3.6 years (+/- SD), duration of diabetes 14.2 +/- 5.7 years) and 75 age-matched healthy nondiabetic subjects (28 men and 47 women). High-sensitive C-reactive protein (hs-CRP) levels were measured with a latex-enhanced immunonephelometer. RESULTS: The patients with type 1 diabetes had significantly higher hs-CRP levels (median 0.35, range 0.05-1.47 mg/l vs. median 0.14, range 0.05-1.44 mg/l; P = 0.001) as well as significantly higher mean IMT and max IMT than the nondiabetic subjects (mean IMT 0.76 +/- 0.09 vs. 0.72 +/- 0.04 mm, P = 0.003; max IMT 0.84 +/- 0.11 vs. 0.77 +/- 0.06 mm, P < 0.0001). Hs-CRP levels were significantly correlated with the mean and max IMT of patients with type 1 diabetes and with the max IMT of nondiabetic patients. Multivariate regression analyses for both diabetic and nondiabetic subjects as a single group showed that hs-CRP levels are independently correlated with the mean IMT and max IMT levels (P = 0.002 and P = 0.023, respectively) as well as with diastolic blood pressure, sex, and duration of diabetes. CONCLUSIONS: Our data indicate that hs-CRP levels are elevated in young patients with type 1 diabetes, possibly corresponding with early-stage advanced carotid atherosclerosis.

Protein kinase C-dependent, CCAAT/enhancer-binding protein beta-mediated expression of insulin-like growth factor I gene.

The possible involvement of the protein kinase C (PKC) pathway in transcriptional regulation of the human insulin-like growth factor-I (IGF-I) gene has been suggested. In this study, we sought to determine whether a PKC-dependent pathway is implicated in the transcriptional control, and if it is, how this occurs. Treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) caused an increase in the activity of the human IGF-I gene major promoter in HepG2 cells. A CCAAT/enhancer-binding protein (C/EBP) binding site located at +22 to +30 was bound by C/EBP beta in a TPA-dependent manner and was solely responsible for the TPA responsiveness. This increase in C/EBP beta activity occurs through transcriptional and posttranslational regulation, and the latter is mediated by activation of p90 ribosomal S6 kinase (RSK): co-expression of dominant negative RSK abolished the TPA-responsive and C/EBP beta-dependent transactivation. Also, TPA-responsive activation of GAL4-C/EBP beta chimera required the Ser residue known as the RSK target. In SK-N-MC cells, which display constitutive, high expression of IGF-I on use of the major promoter, a large amount of C/EBP beta binding was observed with the C/EBP site in the basal state. Treatment with PKC inhibitors substantially reduced the promoter activity and mRNA amounts of IGF-I, with the binding of C/EBP beta to the C/EBP site also being reduced. When the C/EBP site was disrupted, the basal promoter activity was reduced, but the reduction by the PKC inhibitor was no longer observed. These observations suggest that the increase of C/EBP beta binding to the C/EBP site, which is in part mediated via activation of RSK, can primarily explain the TPA responsiveness of the IGF-I gene promoter. The intrinsic PKC activity in SK-N-MC cells should play a major role in the constitutive, high expression of IGF-I and may therefore contribute in part to the maintenance of the tumor phenotype of the cells.