Calreticulin transacetylase catalyzed activation of rat tracheal smooth muscle cell nitric oxide synthase by acetoxycoumarins

The Transacetylase function of Calreticulin (CR) catalyzing the transfer of acetyl groups from acetoxycoumarins (AC) to certain proteins was identified for the first time in our laboratory. Protein acetyltransferase action of CR was termed Calreticulin Transacetylase (CRTAase). In the present work, CRTAase of rat tracheal smooth muscle cells (TSMC) was characterized with respect to the specificity for various AC and its role in the activation of nitric oxide synthase (NOS). 7,8-Diacetoxy-4-methylcoumarin (DAMC), a model AC, when incubated with TSMC along with L-arginine caused profound activation of NOS as compared to that with L-arginine alone. Further, the inclusion of N-omega-nitro-L-arginine methyl ester (L-NAME) along with DAMC resulted in the reduction of NO levels of TSMC to that of control, there by confirming the activation of TSMC NOS. Also, several AC were found to activate TSMC NOS in tune with their specificities to CRTAase. The results presented in this paper bear evidence for the activation of TSMC NOS by AC and their effectiveness to enhance NO of airway cells may be expected to find useful applications in respiratory diseases

The role of calreticulin transacetylase in the activation of human platelet nitrite reductase by polyphenolic acetates

Our earlier investigations demonstrated the remarkable activation of cytochrome P-450 reductase and nitric oxide synthase by 7,8-diacetoxy-4-methylcoumarin, a model polyphenolic acetate by way of acetylation, catalyzed by the Calreticulin. Protein acetyltransferase action of Calreticulin was hence termed Calreticulin transacetylase (CRTAase). Nitric oxide synthase and nitrite reductase are now considered as parts of nitric oxide cycle. The activation of platelets nitric oxide synthase by 7,8-diacetoxy-4-methylcoumarin has already been demonstrated by us. Also, there are reports that certain proteins such as cytochrome P-450 reductase and cytochrome P-450 are endowed with the nitrite reductase activity in mammalian cells. Keeping these facts in view, we turned our attention to probe whether 7,8-diacetoxy-4-methylcoumarin could alter the levels of nitric oxide independent of the action of nitric oxide synthase in the human platelets model. The incubation of 7,8-diacetoxy-4-methylcoumarin and nitrite with platelets caused significant elevation of nitric oxide and cyclic guanosine monophosphate levels possibly due to the activation of nitrite reductase. Several polyphenolic acetates were similarly found to activate the nitrite reductase in tune with their affinities as substrate to CRTAase. N-omega-Nitro-L-arginine methyl ester, the inhibitor of nitric oxide synthase, failed to reverse such an effect of 7,8-diacetoxy-4-methylcoumarin. Clotrimazole which is known to be an inhibitor of nitrite reductase, effectively abolished the 7,8-diacetoxy-4-methylcoumarin mediated enhancement of nitric oxide levels in platelets as well as the nitric oxide mediated effects; such as cyclic guanosine monophosphate levels as well as adenosine diphospate induced platelets aggregation due to nitrite

The competence of 7,8-diacetoxy-4-methylcoumarin and other polyphenolic acetates in mitigating the oxidative stress and their role in angiogenesis

The potential role of polyphenolic acetate (PA) in causing diverse biological and pharmacological actions has been well studied in our laboratory. Our investigations, for the first time, established the role of calreticulin transacetylase (CRTAase) in catalyzing the acetylation of nitric oxide synthase (NOS) by Pas leading to robust activation of NOS. 7, 8-Diacetoxy-4-methylcoumarin (DAMC) and other acetoxycoumarins augmented the expression of thioredoxin (TRX) and vascular endothelial growth factor (VEGF) in human peripheral blood mononuclear cells (PBMCs). These findings substantiated our earlier observations that DAMC was a superb inducer of angiogenesis. The enhanced expression of thioredoxin reductase (TRXR) and diminished expression of thioredoxin interacting protein (TRXIP) leading to increased expression and activity of TRX in PBMCs due to the action of DAMC was revealed by real time RT-PCR analysis. The possible activation of TRX due to acetylation was confirmed by the fact that TRX activity of PBMCs was enhanced by variousacetoxycoumarins in tune with their affinities to CRTAase as substrates. DAMC caused enhanced production of NO by way of acetylation of NOS as mentioned above and thereby acted as an inducer of VEGF. Real time RT-PCR and VEGF ELISA results also revealed the overexpression of TRX. DAMC and other PAs were found to reduce the oxidative stress in cells as proved by significant reduction of intracellular ROS levels. Thus, the crucial role of TRX in DAMC-induced angiogenesis with the involvement of VEGF was established