Increased levels of protein kinase C in lymphocytes in asthma: possible mechanism of regulation

Asthma is an inflammatory disease of the airways. Activation of lymphocytes leads to elaboration of inflammatory mediators which are likely to initiate and perpetuate the asthmatic response. During activation of lymphocytes, the role of protein kinase C (PKC) has been emphasized. Therefore, changes in PKC activity in peripheral blood lymphocytes in bronchial asthma can be expected, which may be due to alterations in the regulatory mechanisms of the enzyme molecule. To understand the mechanism of regulation of PKC activity the effects of drugs, such as carbachol, histamine, sphingosine and disodium cromoglycate (DSCG), on the lymphocytes of healthy subjects were studied. The study included 27 asthmatic patients and 14 healthy volunteers. Disease was classified as mild, moderate-to-severe, and cases in remission. PKC activity was determined in peripheral blood lymphocytes by [3H] phorbol 12,13-dibutyrate ([3H]PDBu)-binding assay. A highly significant (p < 0.001) increase was observed in total, cytosolic and membrane PKC activity in all of the asthmatic patients as compared to the healthy group. There was an increased translocation of PKC from cytosol to membrane in all of the groups, and the extent of translocation of the enzyme indicates physiological activation of the cells. A highly significant (p < 0.001) reciprocal relationship (r = -0.47) existed between forced expiratory volume in one second (FEV1) as percentage predicted and total PKC activity in bronchial asthma. Carbachol and histamine significantly (p < 0.001) increased PKC activity in lymphocytes, the increase being dose-dependent for histamine. Sphingosine or disodium cromoglycate (DSCG) brought about complete inhibition of PKC activity at 100 nM. We conclude that protein kinase C activity is increased in lymphocytes in bronchial asthma. Our findings suggest that the mediators (carbachol and histamine), and drugs (sphingosine and disodium cromoglycate) possibly exert their action on protein kinase C by influencing the regulatory domain of the enzyme.