CAMP receptor proteins and protein kinases in human lymphocytes: fundamental alterations in chronic lymphocytic leukemia cells.

Abstract

To study the significance of cAMP receptor proteins and protein kinase activities in tumor dys‐differentiation peripheral blood lymphocytes from normal donors and from patients with chronic lymphocytic leukemia were isolated by Percoll gradient centrifugation, and analyzed, Both normal and tumor lymphocyte populations were devoid of cell proliferation.Normal human lymphocytes contained about equal activities of histone kinase and ‘casein kinase’, Of the total histone kinase, cAMP‐dependent activity in normal and tumor lymphocytes comprised about 50% as shown by the use of the heat‐stable inhibitor. The tumor lymphocytes, however, exhibited drastically reduced values of all three protein kinase activities, the most pronounced decrease (to 7% of the normal control cells) being observed with the ‘casein kinase’.Total high‐affinity camp‐binding sites (= regulatory subunits R of camp‐dependent protein kinases type I and II) in leukemic lymphocytes were also strongly reduced (to <20%) Immunotitration with specific antibodies raised against rabbit muscle RI regulatory subunits in both normal and leukemic lymphocytes. Immuno‐reactive RII components comprised about 40% of total binding sites in lymphocytes o chronic lymphocytic leukemia, but only 20% in normal cells, the residual 20% being represented by RI protein of low immunoreactivity. Combination of gel elctrophoretic analysis of the camp‐binding proteins labeled with [32P]n3camp and binding to the R‐specific antibodies allowed the identification fo individual type I and type II R proteins: Besides the regulatory subunit RI of 49 kDa present in both cell types, additional isoproteins wwere found, the predominat RII form being a 52kDa subunit in normal lymphocytes and a 50‐kDa subunit in leukemic lymphocytes.The findings in lymphocytes of chronic lymphocytic leukemia cannot be explained by the fact that they are B‐type lymphocytes.Control experiments reveled that normal B cell do not differ significantly from total blood lymphocytes with respect to the parameters mentioned above.Biochemical correlates of the dys‐differentiated status of these non‐proliferating (G0) cell from patients with chronic lymphocytic leukemia, then, are represented by reduced levels of protein kinases, of basal cAMP as well as by changes of the R‐protein pattern. The data indicate that both protein kinases type I and type II may relate to the state of differentiation, independently from cell proliferation.