Cx43 and AKAP95 regulate G1/S conversion by competitively binding to cyclin E1/E2 in lung cancer cells.

BACKGROUND: This study aimed to overexpress or silence connexin 43 (Cx43) and A-kinase anchoring protein 95 (AKAP95) in human A549 cells to explore their effects on cyclins and on G1/S conversion when the interrelationship of Cx43, AKAP95, and cyclin E1/E2 changes. METHODS: The study mainly used Western blot analysis and Co-immuno precipitation to detect the target protein in Cx43/AKAP95 over expressed human A549 cells, and the relationship of proteins Cx43, AKAP95 and Cyclin E during G1-S phase was explored with qualitative and quantitative analysis. RESULTS: The overexpression of Cx43 inhibited the expression of cyclin D1 and E1 by accelerating their degradation and reduced the Cdk2 activity that blocked the DNA transcription activity. However, the overexpression of AKAP95 increased the expression of cyclin D1 and E1 and inhibited their degradation, and enhanced the Cdk2 activity that promoted the DNA transcription activity. Cx43 and AKAP95 competitively bound to cyclin E1/E2, and the competitive binding affected the Cdk2 activity, Rb phosphorylation, DNA transcription activity, and G1/S conversion. CONCLUSIONS: This study showed that the expression of ERK1/2, PKA, and PKB increased when BEAS-2B cells were treated with PDGF-BB, suggesting that ERK1/2, PKA, and PKB might be involved in the binding of AKAP95 with cyclin E, or the separation of AKAP95 from Cx43 from cyclin E1/E2. The specific mechanism underlying this process still needs further exploration.

PDE4 and Epac1 Synergistically Promote Rectal Carcinoma via the cAMP Pathway.

OBJECTIVE: To assess the expression levels of exchange protein 1 directly activated by cAMP (Epac1) and phosphodiesterase 4 (PDE4) in rectal carcinoma, and their associations with clinicopathological indexes. In addition, the associations of PDE4 and Epac1 with A-kinase anchor protein 95, connexin 43, cyclin D1, and cyclin E1 were evaluated. METHODS: The PV-9000 two-step immunohistochemistry method was used to determine protein expression in 44 rectal carcinoma tissue samples and 16 paracarcinoma tissue specimens. RESULTS: The positive rate of PDE4 protein expression in rectal carcinoma tissues was higher than that of paracarcinoma tissues (59.09% vs. 12.5%, P < 0.05). Similar findings were obtained for Epac1 (55% vs. 6.25%, P < 0.05). No significant associations of PDE4 and Epac1 with degree of differentiation, histological type, and lymph node metastasis were found in rectal carcinoma (P > 0.05). Correlations between PDE4 and Epac1, PDE4 and Cx43, PDE4 and cyclin E1, and Epac1 and Cx43 were observed (all P < 0.05). There was no correlation between the other protein pairs examined (P > 0.05). CONCLUSION: PDE4 and Epac1 expression levels are increased in rectal carcinoma tissues, suggesting that the two proteins may be involved in the development of this malignancy. Meanwhile, correlations between PDE4 and Epac1, PDE4 and Cx43, PDE4 and cyclin E1, and Epac1 and Cx43 suggested synergistic effects of these proteins in promoting rectal carcinoma.

Epac1 is involved in cell cycle progression in lung cancer through PKC and Cx43 regulation.

INTRODUCTION: The exchange protein directly activated by cAMP (Epac1), a downstream target of the second messenger cAMP, modulates multiple biological effects of cAMP, alone or in cooperation with protein kinase A (PKC). Epac1 is necessary for promoting protein kinase C (PKC) translocation and activation. The aim of the study was to assess the intensity of Epac1 and protein kinase C (PKC) immunoreactivity in lung cancer and para-carcinoma tissues, and their associations with clinical-pathological indexes. Correlations between the immunoreactivity of Epac1, PKC, A-kinase anchor protein 95 (AKAP95) and connexin43 (Cx43) were also examined. MATERIAL AND METHODS: Epac1, Cx43 (46 cases) and PKC, AKAP95 (45 cases) immunoexpression levels were determined in tissue samples of lung cancer and in 12 samples of neighboring para-carcinoma specimens by the PV-9000 Two-step immunohistochemical technique. RESULTS: The percentage of Epac1 positive samples was significantly lower in lung cancer tissue than in neighboring para-carcinoma specimens (37% vs. 83.3%, p < 0.05); the difference in PKC immunoreactivity was not significant (64.4% vs. 91.7%). Epac1 expression was associated with the degree of malignancy and lymph node metastasis (P < 0.05), but not with histological type (P > 0.05), whereas PKC expression was not related to these parameters. Interestingly, Epac1 expression was correlated with PKC and Cx43 expression. Moreover, PKC expression was correlated with AKAP95 expression. CONCLUSION: Normal Epac1 expression may suppress lung cancer occurrence and metastasis, and its downregulation is involved in cell cycle progression in lung cancer through PKC and Cx43 regulation.